Redline Stealer: A Novel Method

Authored by Mohansundaram M and Neil Tyagi

A brand new packed variant of the Redline Stealer trojan was noticed within the wild, leveraging Lua bytecode to carry out malicious habits.
McAfee telemetry information reveals this malware pressure could be very prevalent, masking North America, South America, Europe, and Asia and reaching Australia.

An infection Chain

 

• GitHub was being abused to host the malware file at Microsoft’s official account within the vcpkg repository https[:]//github[.]com/microsoft/vcpkg/recordsdata/14125503/Cheat.Lab.2.7.2.zip

• McAfee Net Advisor blocks entry to this malicious obtain
• Cheat.Lab.2.7.2.zip is a zipper file with hash 5e37b3289054d5e774c02a6ec4915a60156d715f3a02aaceb7256cc3ebdc6610
• The zip file incorporates an MSI installer.

• The MSI installer incorporates 2 PE recordsdata and a purported textual content file.
  
• Compiler.exe and lua51.dll are binaries from the Lua venture. Nonetheless, they’re modified barely by a risk actor to serve their function; they’re used right here with readme.txt (Which incorporates the Lua bytecode) to compile and execute at Runtime.
• Lua JIT is a Simply-In-Time Compiler (JIT) for the Lua programming language.
  
• The magic quantity 1B 4C 4A 02 usually corresponds to Lua 5.1 bytecode.
• The above picture is readme.txt, which incorporates the Lua bytecode. This method gives the benefit of obfuscating malicious stings and avoiding using simply recognizable scripts like wscript, JScript, or PowerShell script, thereby enhancing stealth and evasion capabilities for the risk actor.
• Upon execution, the MSI installer shows a person interface.

• Throughout set up, a textual content message is displayed urging the person to unfold the malware by putting in it onto a pal’s laptop to get the total software model.

• Throughout set up, we will observe that three recordsdata are being written to Disk to C:program FilesCheat Lab Inc Cheat Lab path.

• Beneath, the three recordsdata are positioned inside the brand new path.

 

• • Right here, we see that compiler.exe is executed by msiexec.exe and takes readme.txt as an argument. Additionally, the Blue Highlighted half reveals lua51.dll being loaded into compiler.exe. Lua51.dll is a supporting DLL for compiler.exe to operate, so the risk actor has shipped the DLL together with the 2 recordsdata.
    

• • Throughout set up, msiexec.exe creates a scheduled activity to execute compiler.exe with readme.txt as an argument.
  • Other than the above approach for persistence, this malware makes use of a 2^nd fallback approach to make sure execution.
  • It copies the three recordsdata to a different folder in program information with a really lengthy and random path.

• Be aware that the identify compiler.exe has been modified to NzUW.exe.
• Then it drops a file ErrorHandler.cmd at C:WindowsSetupScripts
• The contents of cmd may be seen right here. It executes compiler.exe below the brand new identify of NzUw.exe with the Lua byte code as a parameter.

• Executing ErrorHandler.cmd makes use of a LolBin within the system32 folder. For that, it creates one other scheduled activity.

 

• • The above picture reveals a brand new activity created with Home windows Setup, which can launch C:Windowssystem32oobeSetup.exe with none argument.
  • Seems, if you happen to place your payload in c:WINDOWSSetupScriptsErrorHandler.cmd, c:WINDOWSsystem32oobeSetup.exe will load it at any time when an error happens.
    

 

Supply: Add a Customized Script to Home windows Setup | Microsoft Study

• • c:WINDOWSsystem32oobeSetup.exe is anticipating an argument. When it isn’t offered, it causes an error, which ends up in the execution of ErrorHandler.cmd, which executes compiler.exe, which hundreds the malicious Lua code.
  • We will affirm this within the beneath course of tree.
    

We will affirm that c:WINDOWSsystem32oobeSetup.exe launches cmd.exe with ErrorHandler.cmd script as argument, which runs NzUw.exe(compiler.exe)

• • It then checks the IP from the place it’s being executed and makes use of ip-API to realize that.

 

• • We will see the community packet from api-api.com; that is written as a JSON object to Disk within the inetCache folder.
    

• • We will see procmon logs for a similar.
    

• We will see JSON was written to Disk.

C2 Communication and stealer exercise

• • Communication with c2 happens over HTTP.

• • We will see that the server despatched the duty ID of OTMsOTYs for the contaminated machine to carry out. (on this case, taking screenshots)
    
  • A base64 encoded string is returned.

• • 

• • An HTTP PUT request was despatched to the risk actors server with the URL /loader/display.
  • IP is attributed to the redline household, with many engines marking it as malicious.
    
    

• Additional inspection of the packet reveals it’s a bitmap picture file.
• The identify of the file is Display screen.bmp
• Additionally, observe the distinctive person agent used on this put request, i.e., Winter

• After Dumping the bitmap picture useful resource from Wireshark to disc and opening it as a .bmp(bitmap picture) extension, we see.
• The screenshot was despatched to the risk actors’ server.

Evaluation of bytecode File

• It’s difficult to get the true decomplication of the bytecode file.
• Many open supply decompilers have been used, giving a barely totally different Lua script.
• The script file was not compiling and throwing some errors.

• The script file was sensitized based mostly on errors in order that it may very well be compiled.

• One desk (var_0_19) is populated by passing information values to 2 capabilities.
• Within the console output, we will see base64 encoded values being saved in var_0_19.
• These base64 strings decode to extra encoded information and to not plain strings.

• All information in var_0_19 is assigned to var_0_26

• • The identical approach is populating 2nd desk (var_0_20)
  • It incorporates the substitution key for encoded information.
    

• • The above pic is a decryption loop. It iterates over var_0_26 component by component and decrypts it.
  • This loop can be very lengthy and incorporates many junk traces.
  • The loop ends with assigning the decrypted values again to var_0_26.
    
    

 

• • We place the breakpoint on line 1174 and watch the values of var_0_26.
    

• • As we hit the breakpoint a number of instances, we see extra encoded information decrypted within the watch window.
    

 

• We will see decrypted strings like Tamper Detected! In var_0_26

Loading luajit bytcode:

Earlier than loading the luajit bytecode, a brand new state is created. Every Lua state maintains its world surroundings, stack, and set of loaded libraries, offering isolation between totally different situations of Lua code.

It hundreds the library utilizing the Lua_openlib operate and hundreds the debug, io, math,ffi, and different supported libraries,
Lua jit bytecode loaded utilizing the luaL_loadfile export operate from lua51. It makes use of the fread operate to learn the jit bytecode, after which it strikes to the allotted reminiscence utilizing the memmove operate.
 
The bytecode from the readme. Textual content is moved randomly, altering the bytecode from one offset to a different utilizing the memmove API operate. The precise size of 200 bytes from the Jit bytecode is copied utilizing the memmove API operate.

It took desk values and processed them utilizing the beneath floating-point arithmetic and xor instruction.
It makes use of memmove API capabilities to maneuver the bytes from the supply to the vacation spot buffer.
After additional evaluation, we discovered that c definition for variable and arguments which might be used on this script.
Now we have seen some API definitions, and it makes use of ffi for instantly accessing Home windows API capabilities from Lua code, examples of defining API capabilities,
 

It creates the mutex with the identify winter750 utilizing CreateMutexExW.
It Hundreds the dll at Runtime utilizing the LdrLoaddll operate from ntdll.dll. This operate known as utilizing luajit ffi.
It retrieves the MachineGuid from the Home windows registry utilizing the RegQueryValueEx operate by utilizing ffi. Opens the registry key “SOFTWAREMicrosoftCryptography” utilizing RegOpenKeyExA—queries the worth of “MachineGuid” from the opened registry key.
It retrieves the ComputerName from the Home windows registry utilizing the GetComputerNameA operate utilizing ffi.
It gathers the next data and sends it to the C2 server.
It additionally sends the next data to the c2 server,

• On this weblog, we noticed the assorted strategies risk actors use to infiltrate person methods and exfiltrate their information.
• Microsoft has since eliminated these recordsdata from the repositories.

Indicators of Compromise

Cheat.Lab.2.7.2.zip	5e37b3289054d5e774c02a6ec4915a60156d715f3a02aaceb7256cc3ebdc6610
Cheat.Lab.2.7.2.zip	https[:]//github[.]com/microsoft/vcpkg/recordsdata/14125503/Cheat.Lab.2.7.2.zip
lua51.dll	873aa2e88dbc2efa089e6efd1c8a5370e04c9f5749d7631f2912bcb640439997
readme.txt	751f97824cd211ae710655e60a26885cd79974f0f0a5e4e582e3b635492b4cad
compiler.exe	dfbf23697cfd9d35f263af7a455351480920a95bfc642f3254ee8452ce20655a
Redline C2	213[.]248[.]43[.]58
Trojanised Git Repo	hxxps://github.com/microsoft/STL/recordsdata/14432565/Cheater.Professional.1.6.0.zip