PseudoSigner01PEIntro10Anorganix

Hunt Hypothesis

This hypothesis targets the execution of PE files exhibiting specific structural anomalies or “pseudo-signing” characteristics, which adversaries may use to bypass basic integrity checks or blend in with legitimate software. Proactively hunting for these files in Azure Sentinel helps identify low-fidelity malware or trojans that rely on subtle binary manipulations to evade initial detection, ensuring early containment of stealthy threats.

YARA Rule

rule PseudoSigner01PEIntro10Anorganix
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 8B 04 24 9C 60 E8 14 00 00 00 5D 81 ED 0A 45 40 90 80 BD 67 44 40 90 90 0F 85 48 FF ED 0A 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 legacy Java or .NET application (e.g., an internal HR portal or legacy ERP system) is updated via a CI/CD pipeline that uses a generic build tool to embed metadata or version strings into the PE header, inadvertently creating a pattern that matches the “Anorganix” signature due to specific byte alignments in the intro section.

  • Filter/Exclusion: Exclude files located in the application’s specific installation directory (e.g., C:\Program Files\InternalHR\bin\) if the executable name matches known application binaries (e.g., hrapp.exe, erp_service.dll) and the file size is within the expected range for that specific version.

• Scenario: An automated backup or snapshot agent (e.g., Veeam, Commvault, or Windows Server Backup) creates a temporary copy of a running executable file during a deduplication or compression process, resulting in a truncated or partially written PE file that triggers the pseudo-signature due to incomplete header data.

  • Filter/Exclusion: Exclude files with extensions commonly used for temporary backups or snapshots (e.g., .tmp, .bak, .vbk, .vib) or files located in designated backup staging directories (e.g., C:\BackupStaging\, D:\VeeamBackups\) that are not directly executed by user processes.

• Scenario: A developer or DevOps engineer uses a lightweight PE editor tool (e.g., PE-bear, CFF Explorer, or a custom Python script using pefile) to patch or inject a small library into a test build of a microservice executable before deployment to a staging environment.

  • Filter/Exclusion: Exclude events where the parent process is a known development or build tool (e.g., python.exe, node.exe, msbuild.exe, dotnet.exe) and the