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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 knowledge exhibits this malware pressure may be very prevalent, overlaying North America, South America, Europe, and Asia and reaching Australia.

An infection Chain

 

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

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

  • The MSI installer comprises 2 PE information 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 comprises 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 comprises 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 consumer interface.

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

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

  • Beneath, the three information 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 exhibits lua51.dll being loaded into compiler.exe. Lua51.dll is a supporting DLL for compiler.exe to perform, so the risk actor has shipped the DLL together with the 2 information.
    • Throughout set up, msiexec.exe creates a scheduled activity to execute compiler.exe with readme.txt as an argument.
    • Other than the above method for persistence, this malware makes use of a 2nd fallback method to make sure execution.
    • It copies the three information to a different folder in program knowledge with a really lengthy and random path.
  • Notice 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 could be seen right here. It executes compiler.exe beneath 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 exhibits a brand new activity created with Home windows Setup, which is able to 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 every time an error happens.

 

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

    • c:WINDOWSsystem32oobeSetup.exe is anticipating an argument. When it’s not supplied, it causes an error, which results in the execution of ErrorHandler.cmd, which executes compiler.exe, which hundreds the malicious Lua code.
    • We will verify this within the under course of tree.

We will verify 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 exhibits it’s a bitmap picture file.
  • The identify of the file is Display screen.bmp
  • Additionally, notice the distinctive consumer 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 had been used, giving a barely completely different Lua script.
  • The script file was not compiling and throwing some errors.

  • The script file was sensitized primarily based on errors in order that it might be compiled.

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

  • All knowledge in var_0_19 is assigned to var_0_26

    • The identical method is populating 2nd desk (var_0_20)
    • It comprises the substitution key for encoded knowledge.
    • 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 comprises 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 knowledge 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 international surroundings, stack, and set of loaded libraries, offering isolation between completely different cases of Lua code.

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

It took desk values and processed them utilizing the under floating-point arithmetic and xor instruction.
It makes use of memmove API features 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 will likely be used on this script.
We now have seen some API definitions, and it makes use of ffi for straight accessing Home windows API features from Lua code, examples of defining API features,
 

It creates the mutex with the identify winter750 utilizing CreateMutexExW.
It Masses the dll at Runtime utilizing the LdrLoaddll perform from ntdll.dll. This perform is known as utilizing luajit ffi.
It retrieves the MachineGuid from the Home windows registry utilizing the RegQueryValueEx perform through the use of 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 perform 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 varied strategies risk actors use to infiltrate consumer programs and exfiltrate their knowledge.

Indicators of Compromise

Cheat.Lab.2.7.2.zip 5e37b3289054d5e774c02a6ec4915a60156d715f3a02aaceb7256cc3ebdc6610
Cheat.Lab.2.7.2.zip https[:]//github[.]com/microsoft/vcpkg/information/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/information/14432565/Cheater.Professional.1.6.0.zip

 

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