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These threat actors show perfect usage of the Spanish language in the emails they send, they only target Colombian entities, and they use premade malware and don’t develop any themselves. | [] | Operation Spalax Targeted malware attacks in Colombia |
Attack overview Targets are approached with emails that lead to the download of malicious files. | [] | Operation Spalax Targeted malware attacks in Colombia |
In most cases, these emails have a PDF document attached, which contains a link that the user must click to download the malware. | [
"T1204.002",
"T1566.001"
] | Operation Spalax Targeted malware attacks in Colombia |
The downloaded files are regular RAR archives that have an executable file inside. | [
"T1027"
] | Operation Spalax Targeted malware attacks in Colombia |
These archives are hosted in legitimate file hosting services such as OneDrive or MediaFire. | [] | Operation Spalax Targeted malware attacks in Colombia |
The target has to manually extract the file and execute it for the malware to run. | [
"T1204.002"
] | Operation Spalax Targeted malware attacks in Colombia |
We’ve found a variety of packers used for these executables, but their purpose is always to have a remote access trojan running on the victimized computer, usually by decrypting the payload and injecting it into legitimate processes. | [
"T1027",
"T1055",
"T1140"
] | Operation Spalax Targeted malware attacks in Colombia |
An overview of a typical attack is shown in Figure 1. | [] | Operation Spalax Targeted malware attacks in Colombia |
We have seen the attackers use three different RATs: Remcos, njRAT and AsyncRAT. Figure 1. | [] | Operation Spalax Targeted malware attacks in Colombia |
Overview of the attack Phishing emails The attackers use various topics for their emails, but in most cases they are not specially crafted for their victims. | [] | Operation Spalax Targeted malware attacks in Colombia |
On the contrary, most of these emails have generic topics that could be reused for different targets. | [] | Operation Spalax Targeted malware attacks in Colombia |
We found phishing emails with these topics: A notification about a driving infraction A notification to take a mandatory COVID-19 test A notification to attend a court hearing An open investigation against the recipient for misuse of public funds A notification of an embargo of bank accounts The email shown in Figure 2... | [] | Operation Spalax Targeted malware attacks in Colombia |
There is a PDF file attached that promises a photo of the infraction, as well as information about time and place of the incident. | [
"T1566.001"
] | Operation Spalax Targeted malware attacks in Colombia |
The sender has been spoofed to make the email look like it is coming from SIMIT (a system for paying transit violations in Colombia). | [] | Operation Spalax Targeted malware attacks in Colombia |
Example of a phishing email The pdf file only contains an external link that has been shortened with the acortaurl service, as shown in Figure 3. | [] | Operation Spalax Targeted malware attacks in Colombia |
The shortened URL is: https://acortaurl[.]com/httpsbogotagovcohttpsbogotagovcohttpsbogotagovco. | [] | Operation Spalax Targeted malware attacks in Colombia |
After the shortened link is expanded, a RAR archive is downloaded from: http://www.mediafire[.]com/file/wbqg7dt604uwgza/SIMITcomparendoenlineasimitnumeroreferenciaComparendo2475569.uue/file. | [
"T1027"
] | Operation Spalax Targeted malware attacks in Colombia |
PDF attached to phishing email Figure 4 shows part of the email’s header. | [] | Operation Spalax Targeted malware attacks in Colombia |
The spoofed sender is notificacionesmultas@simit.org[.]co but we can see that the real sender is IP address 128.90.108[.]177, which is connected with the domain name julian.linkpc[.]net, as found in historic DNS data. | [] | Operation Spalax Targeted malware attacks in Colombia |
It’s not a coincidence that the same domain name is used for contacting the C&C server in the malicious sample contained in the RAR archive. | [] | Operation Spalax Targeted malware attacks in Colombia |
This IP address belongs to Powerhouse Management, a VPN service provider. | [] | Operation Spalax Targeted malware attacks in Colombia |
Header of a phishing email In more recent emails, the shortened link in the PDF file resolves to https://bogota.gov[.]co (a legitimate site) when visited from outside of Colombia. | [] | Operation Spalax Targeted malware attacks in Colombia |
Also, in some cases the GetResponse service has been used to send the email. | [] | Operation Spalax Targeted malware attacks in Colombia |
This is probably done to track whether the victim has clicked on the link. | [] | Operation Spalax Targeted malware attacks in Colombia |
In these cases there is no attachment: a link to the GetResponse platform leads to the download of malware. | [] | Operation Spalax Targeted malware attacks in Colombia |
You can see the other emails in the following gallery (click to enlarge): Figures 5 to 13. | [] | Operation Spalax Targeted malware attacks in Colombia |
Various phishing emails and their attached files Malicious artifacts Droppers The executable files contained in compressed archives that are downloaded via the phishing emails are responsible for decrypting and running remote access trojans on a victimized computer. | [
"T1027",
"T1140"
] | Operation Spalax Targeted malware attacks in Colombia |
In the following sections, we describe the various droppers we have seen. | [] | Operation Spalax Targeted malware attacks in Colombia |
NSIS installers The dropper that is most commonly used by these attackers comes as a file that was compiled with NSIS (Nullsoft Scriptable Install System). | [] | Operation Spalax Targeted malware attacks in Colombia |
To try to evade detection, this installer contains several benign files that are written to disk (they are not part of NSIS binaries and they are not used at all by the installer) and two files that are malicious: an encrypted RAT executable and a DLL file that decrypts and runs the trojan. | [
"T1027"
] | Operation Spalax Targeted malware attacks in Colombia |
An NSIS script for one of these installers is shown in Figure 14. | [] | Operation Spalax Targeted malware attacks in Colombia |
The benign files are usually different in different droppers used by the attackers. | [] | Operation Spalax Targeted malware attacks in Colombia |
NSIS script for one of the droppers; the malicious files are highlighted The files Bonehead (encrypted RAT) and ShoonCataclysm.dll (dropper DLL) are written in the same folder and the DLL is run with rundll32.exe using Uboats as its argument. | [
"T1218.011"
] | Operation Spalax Targeted malware attacks in Colombia |
The names of these files change between executables. | [] | Operation Spalax Targeted malware attacks in Colombia |
Some more examples are: rundll32.exe | [] | Operation Spalax Targeted malware attacks in Colombia |
Blackface,Breathing rundll32.exe OximeLied,Hostage rundll32.exe Conservatory,Piggins | [] | Operation Spalax Targeted malware attacks in Colombia |
We used the name of the benign files contained in some of these NSIS installers to find more malicious installers used by the Spalax operators. | [] | Operation Spalax Targeted malware attacks in Colombia |
Table 1 lists details of three different NSIS installers used by the attackers that contained all the same benign files. | [] | Operation Spalax Targeted malware attacks in Colombia |
The only difference among them was the encrypted file, which pointed to different C&C servers. | [] | Operation Spalax Targeted malware attacks in Colombia |
NSIS installers with identical benign files used by this group SHA-1C&C | [] | Operation Spalax Targeted malware attacks in Colombia |
6E81343018136B271D1F95DB536CA6B2FD1DFCD6marzoorganigrama20202020.duckdns[.]org 7EDB738018E0E91C257A6FC94BDBA50DAF899F90ruthy.qdp6fj1uji[.]xyz 812A407516F9712C80B70A14D6CDF282C88938C1dominoduck2098.duckdns[.]org | [] | Operation Spalax Targeted malware attacks in Colombia |
However, we also found malicious NSIS installers used by other unrelated groups that had the same benign files as the ones used by this group. | [] | Operation Spalax Targeted malware attacks in Colombia |
Figure 15 lists the files contained in two different NSIS installers. | [] | Operation Spalax Targeted malware attacks in Colombia |
The one on the left (SHA-1: 3AC39B5944019244E7E33999A2816304558FB1E8) is an executable used by this group and the one on the right (SHA-1: 6758741212F7AA2B77C42B2A2DE377D97154F860) is unrelated. | [] | Operation Spalax Targeted malware attacks in Colombia |
The SHA-1 hashes for all the benign files are the same (and also the filenames) and even the malicious DLL is the same. | [] | Operation Spalax Targeted malware attacks in Colombia |
However, the encrypted file Bonehead is different. | [] | Operation Spalax Targeted malware attacks in Colombia |
Files contained in NSIS droppers from unrelated campaigns This means that these installers were generated with the same builder, but by different actors. | [] | Operation Spalax Targeted malware attacks in Colombia |
The builder is probably offered in underground forums and includes these benign files. | [] | Operation Spalax Targeted malware attacks in Colombia |
This, along with a complete analysis of the dropper, was described earlier this year by Sophos in their RATicate article. | [] | Operation Spalax Targeted malware attacks in Colombia |
There is also an article by Lab52 describing one of the NSIS installers used in Operation Spalax, which they attribute to APT-C-36. | [] | Operation Spalax Targeted malware attacks in Colombia |
In the vast majority of cases these NSIS droppers decrypt and run the Remcos RAT, but we have also seen cases where the payload is njRAT. | [
"T1140"
] | Operation Spalax Targeted malware attacks in Colombia |
These will be described later in the Payloads section. | [] | Operation Spalax Targeted malware attacks in Colombia |
Agent Tesla packers We have seen several droppers that are different variants of a packer that uses steganography and is known to be used in Agent Tesla samples. | [
"T1027"
] | Operation Spalax Targeted malware attacks in Colombia |
Interestingly, the attackers use various payloads, but none of them are Agent Tesla. | [] | Operation Spalax Targeted malware attacks in Colombia |
Even though there are differences in all the samples regarding the layers of encryption, obfuscation or anti-analysis used, we can summarize the actions taken by the droppers as follows: The dropper reads a string (or binary data) from its resource section and decrypts it. | [
"T1027",
"T1140"
] | Operation Spalax Targeted malware attacks in Colombia |
The result is a DLL that will be loaded and called in the same address space. | [
"T1055"
] | Operation Spalax Targeted malware attacks in Colombia |
The DLL reads pixels from an image contained in the first binary and decrypts another executable. | [
"T1027",
"T1140"
] | Operation Spalax Targeted malware attacks in Colombia |
This one is loaded and executed in the same address space. | [] | Operation Spalax Targeted malware attacks in Colombia |
This new executable is packed with CyaX. It reads data from its own resource section and decrypts a payload. | [
"T1027"
] | Operation Spalax Targeted malware attacks in Colombia |
There are anti-analysis checks; if they pass, the payload can be injected into a new process or loaded in the same process space. | [
"T1055"
] | Operation Spalax Targeted malware attacks in Colombia |
The initial dropper is coded in C#. | [] | Operation Spalax Targeted malware attacks in Colombia |
In all the samples that we have seen, the code for the dropper was hiding in non-malicious code, probably copied from other apps. | [
"T1027"
] | Operation Spalax Targeted malware attacks in Colombia |
The benign code is not executed; it’s there to evade detection. | [] | Operation Spalax Targeted malware attacks in Colombia |
In Figure 16 we see an example of the resources contained in one of these droppers. | [] | Operation Spalax Targeted malware attacks in Colombia |
The text in green (only shown partially) is a string that will be decrypted to generate the next stage to be executed and the image that we see below the green text will be decrypted by the second stage malware. | [
"T1140"
] | Operation Spalax Targeted malware attacks in Colombia |
The algorithm used for decryption of the string varies from sample to sample, but sometimes the resource is just an unencrypted binary. | [] | Operation Spalax Targeted malware attacks in Colombia |
Figure 16. | [] | Operation Spalax Targeted malware attacks in Colombia |
Resources contained in Agent Tesla’s packer | [] | Operation Spalax Targeted malware attacks in Colombia |
The method to be executed in the DLL is always named StartGame or StartUpdate. | [] | Operation Spalax Targeted malware attacks in Colombia |
It reads the image from the first executable, and stores every pixel as three numbers according to its red, green and blue components. | [
"T1027"
] | Operation Spalax Targeted malware attacks in Colombia |
Then it decrypts the array by doing a single-byte XOR operation, cycling through the key. | [
"T1140"
] | Operation Spalax Targeted malware attacks in Colombia |
After that, the array is gzip-decompressed and executed. | [
"T1027"
] | Operation Spalax Targeted malware attacks in Colombia |
Part of the code for the mentioned operations is shown in Figure 17. Figure 17. | [] | Operation Spalax Targeted malware attacks in Colombia |
Code to decrypt and run the third-stage malware The third stage is in charge of decrypting and running the payload. | [] | Operation Spalax Targeted malware attacks in Colombia |
The .NET packer known as CyaX is used to perform this task. | [
"T1027"
] | Operation Spalax Targeted malware attacks in Colombia |
The version of the packer used by the attackers is v4, although they used v2 in some cases. | [] | Operation Spalax Targeted malware attacks in Colombia |
Figure 18 shows the hardcoded configuration for one of their samples. | [] | Operation Spalax Targeted malware attacks in Colombia |
Hardcoded configuration in CyaX-Sharp packer | [] | Operation Spalax Targeted malware attacks in Colombia |
The decryption of the payload is based on XOR operations and is the same as the algorithm previously shown but with an extra step: the payload is XORed with its first 16 bytes as a key. | [
"T1140"
] | Operation Spalax Targeted malware attacks in Colombia |
Once it’s decrypted, it can be run in the same address space or injected into a different process, depending on the configuration. | [
"T1055"
] | Operation Spalax Targeted malware attacks in Colombia |
This packer supports various anti-analysis operations such as disabling Windows Defender, checking for security products, and detecting virtual environments and sandboxes. | [
"T1518.001",
"T1562.001"
] | Operation Spalax Targeted malware attacks in Colombia |
The majority of the payloads for these droppers are njRAT, but we have also seen AsyncRAT. | [] | Operation Spalax Targeted malware attacks in Colombia |
We saw Remcos in one of these droppers, but the code in the packer was different. | [] | Operation Spalax Targeted malware attacks in Colombia |
Part of the main routine for the injection of the payload is shown in Figure 19. Figure 19. | [
"T1055"
] | Operation Spalax Targeted malware attacks in Colombia |
Code for the last stage of a dropper We have noticed that the configuration is contained in different variables. | [] | Operation Spalax Targeted malware attacks in Colombia |
Values like #startup_method# or #bind# mean that the configuration was not set for those options. | [] | Operation Spalax Targeted malware attacks in Colombia |
The payload is read from an encrypted resource and XORed with a hardcoded password. | [
"T1027"
] | Operation Spalax Targeted malware attacks in Colombia |
The shellcode that performs the injection is contained in an array and is dynamically loaded. | [
"T1055"
] | Operation Spalax Targeted malware attacks in Colombia |
There are no anti-analysis checks or protection mechanisms. | [] | Operation Spalax Targeted malware attacks in Colombia |
AutoIt | [] | Operation Spalax Targeted malware attacks in Colombia |
droppers For some of their droppers, the attackers have used an AutoIt packer that comes heavily obfuscated. | [
"T1027"
] | Operation Spalax Targeted malware attacks in Colombia |
Unlike the cases that were previously described, in this case the first-stage malware performs the injection and execution of the payload. | [
"T1055"
] | Operation Spalax Targeted malware attacks in Colombia |
It does so by using two shellcodes contained in the compiled AutoIt script: one to decrypt the payload and another to inject it into some process. | [
"T1027",
"T1055",
"T1140"
] | Operation Spalax Targeted malware attacks in Colombia |
The payload is constructed by concatenating several strings, as shown in Figure 20. | [] | Operation Spalax Targeted malware attacks in Colombia |
By inspecting the last two characters, we can see that the string is in reverse order. | [] | Operation Spalax Targeted malware attacks in Colombia |
Figure 20. | [] | Operation Spalax Targeted malware attacks in Colombia |
Concatenation of the payload The routine that decrypts the payload contains a small shellcode that is loaded with VirtualAlloc and executed. | [
"T1106"
] | Operation Spalax Targeted malware attacks in Colombia |
The decryption done by the shellcode is based on a single-byte XOR algorithm. | [
"T1140"
] | Operation Spalax Targeted malware attacks in Colombia |
The code that loads the shellcode is shown in Figure 21. Figure 21. | [] | Operation Spalax Targeted malware attacks in Colombia |
Execution of shellcode to decrypt the payload We can see that the shellcode is stored encrypted. | [
"T1140"
] | Operation Spalax Targeted malware attacks in Colombia |
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