SimbiOZ13Extranger

Hunt Hypothesis

This YARA rule targets the SimbiOZ13Extranger sample, which is associated with the SimbiOZ malware family known for its ability to inject into processes and establish persistence on compromised hosts. Proactively hunting for this signature in Azure Sentinel allows the SOC team to identify low-severity, potentially stealthy infections that may be used as a foothold for lateral movement or data exfiltration before they escalate to more impactful attacks.

YARA Rule

rule SimbiOZ13Extranger
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 57 57 8D 7C 24 04 50 B8 00 [3] AB 58 5F C3 }

condition:
		$a0 at pe.entry_point
}

Deployment Notes

This YARA rule can be deployed in the following contexts:

• Microsoft Defender for Endpoint — Custom indicators / advanced hunting
• Email Gateway — Attachment scanning
• File Share Monitoring — Periodic scanning of shared drives
• YARA CLI — Manual threat hunting on endpoints

This rule contains 1 string patterns in its detection logic.

• Source Rule

False Positive Guidance

• Scenario: A developer or DevOps engineer uses Git for Windows or VS Code to clone or update a repository containing C/C++ source code that includes the #include <windows.h> directive or specific Windows API function names (e.g., CreateFile, ReadFile) which the YARA rule might match as part of its string criteria.

  • Filter/Exclusion: Exclude files located in standard development directories such as C:\Users\*\AppData\Local\Programs\Microsoft VS Code\, C:\Program Files\Git\, or any path containing \.git\, node_modules\, or venv\. Additionally, exclude processes like code.exe, git.exe, or msbuild.exe when they are reading/writing these files.

• Scenario: An IT administrator runs 7-Zip or WinRAR to extract a large archive containing documentation or source code packages (e.g., .zip files with embedded text files) that include specific keyword strings targeted by the rule (such as “SimbiOZ” or common Windows API names) within the extracted files.

  • Filter/Exclusion: Exclude processes like 7z.exe, WinRAR.exe, or tar.exe when the file path ends with common archive extensions (.zip, .rar, .7z, .tar.gz) or when the file is located in temporary extraction directories like C:\Users\*\AppData\Local\Temp\ or C:\Windows\Temp\.

• Scenario: A system administrator uses Notepad++ or Sublime Text to edit a configuration file or script (e.g., a PowerShell or Python script) that contains hardcoded strings or comments matching the YARA rule’s detection patterns (e.g., comments referencing “SimbiOZ” or specific function names).