PEtitev20

Hunt Hypothesis

This YARA rule targets specific characteristics of the PEtitev20 malware, likely indicating the presence of a low-severity threat actor deploying custom or niche payloads within the environment. Proactively hunting for this signature allows the SOC team to identify dormant or stealthy infections that may evade standard behavioral detections, ensuring early containment of targeted threats in Azure Sentinel.

YARA Rule

rule PEtitev20
{
      meta:
		author="malware-lu"
strings:
		$a0 = { B8 [4] 66 9C 60 50 8B D8 03 ?? 68 54 BC [2] 6A ?? FF 50 18 8B CC 8D A0 54 BC [2] 8B C3 8D 90 E0 15 [2] 68 }

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 runs a custom Python script using the pyinstaller tool to bundle a small utility into a standalone executable for distribution to non-technical users. The resulting .exe file often contains embedded Python bytecode and standard library modules that match the generic PE structure patterns in PEtitev20.

  • Filter/Exclusion: Exclude files located in specific build output directories (e.g., C:\Projects\Tools\dist\) or where the parent process is python.exe or pyinstaller.exe and the file extension is .exe but the size is under a certain threshold (e.g., < 10MB), or add an exclusion for known PyInstaller signature hashes.

• Scenario: An IT administrator installs a legacy line-of-business application or a specific vendor-provided agent (e.g., a monitoring agent or backup client) that uses a custom, non-standard PE header layout or includes debug symbols that trigger the YARA rule’s structural checks.

  • Filter/Exclusion: Create a whitelist of known vendor executables by their full path (e.g., C:\Program Files\VendorApp\Agent\agent.exe) or by their specific SHA-256 hash if the vendor provides a static binary.

• Scenario: A scheduled maintenance job runs a C# or C++ compiled utility (e.g., a log rotation script or a database cleanup tool) that is compiled with a specific compiler version or optimization flag that results in a PE structure matching the PEtitev20 pattern, particularly if the binary is small and lacks standard section names.

  • Filter/Exclusion: Exclude executables in the C:\Windows\System32\ or C:\Program Files\ directories that are owned by a trusted service account (e.g., NT AUTHORITY\SYSTEM or a specific `