PseudoSigner01ExeSmasherAnorganix

Hunt Hypothesis

This rule identifies potentially malicious executables that utilize the PseudoSigner01ExeSmasherAnorganix YARA signature, often associated with tools designed to obfuscate or manipulate binary structures to evade static analysis. Proactively hunting for this indicator in Azure Sentinel allows the SOC to detect low-severity, stealthy payloads that may be used for initial access or privilege escalation before they trigger more prominent behavioral alerts.

YARA Rule

rule PseudoSigner01ExeSmasherAnorganix
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 9C FE 03 90 60 BE 90 90 41 90 8D BE 90 10 FF FF 57 83 CD FF EB 10 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 FE 0B E9 }

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 build engineer uses a custom Python script or PowerShell wrapper to strip digital signatures from legacy .exe files before packaging them into a self-extracting archive for deployment. The script uses a library like pywin32 or osslsigncode to remove the Authenticode signature, triggering the “ExeSmasher” heuristic.

  • Filter/Exclusion: Exclude processes running from specific development directories (e.g., C:\Dev\BuildTools\, C:\Users\<dev_user>\AppData\Local\Temp\) or where the parent process is python.exe or pwsh.exe with a command line containing strip_sign or remove_authenticode.

• Scenario: An IT administrator runs a scheduled maintenance job using a third-party utility like NirCmd or SigCheck to verify or reset signatures on application binaries in a shared network folder (\\fileserver\apps\) to resolve “Unknown Publisher” warnings after a patch update.

  • Filter/Exclusion: Exclude executions where the target file path resides in known application share paths (e.g., \\fileserver\apps\, \\fileserver\patches\) and the parent process is cmd.exe or powershell.exe invoked by a scheduled task named AppMaintenance or PatchVerification.

• Scenario: A security team performs a controlled test of their EDR response by using a tool like SigTool or a custom C# console app to remove signatures from a benign test executable (test_exe_no_sig.exe) stored in a dedicated quarantine folder (C:\EDR_Test\Quarantine\).

  • Filter/Exclusion: Exclude files located in specific test or quarantine directories (e.g., C:\EDR_Test\, C:\Temp\Quarantine\) and