PseudoSigner02REALBasicAnorganix

Hunt Hypothesis

This rule identifies potentially malicious or obfuscated code artifacts that leverage specific string patterns or structural anomalies to mimic legitimate signatures, indicating an adversary attempting to evade static analysis. Proactively hunting for these indicators in Azure Sentinel helps detect early-stage implantation or persistence mechanisms that may not yet trigger high-fidelity alerts, reducing the dwell time of low-severity threats within the environment.

YARA Rule

rule PseudoSigner02REALBasicAnorganix
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 55 89 E5 90 90 90 90 90 90 90 90 90 90 50 90 90 90 90 90 00 01 }

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

• Digital Signature Verification in CI/CD Pipelines: Automated build agents (e.g., Jenkins, GitHub Actions, or Azure DevOps) frequently download and verify the authenticity of third-party libraries, container images, or release artifacts using tools like signtool.exe (Windows) or gpg/openssl (Linux). These processes often involve reading certificate chains and verifying hashes, which may match the “pseudo-signer” logic if the rule targets specific cryptographic structures or file headers.

  • Filter/Exclusion: Exclude processes running under known CI/CD service accounts or within specific build directories (e.g., C:\Jenkins\workspace\, /home/runner/work/). Additionally, whitelist parent processes like java.exe, node.exe, or docker.exe when interacting with signature verification tools.

• Enterprise Code Signing for Internal Releases: Development and Release Engineering teams use code signing utilities (e.g., signtool.exe, osslsigncode, or commercial tools like SignCode) to sign internal executables, installers, or driver packages before deployment. This is a standard, legitimate administrative task that involves manipulating certificate data and embedding signatures, potentially triggering rules looking for unusual signing behavior.

  • Filter/Exclusion: Whitelist specific user groups (e.g., “Release Engineers”, “DevOps Team”) or known service accounts used for signing. Exclude processes where the parent is a known build tool or IDE (e.g., msbuild.exe, dotnet.exe, idea64.exe).

• Scheduled Backup and Archive Integrity Checks: Enterprise backup solutions (e.g., Veeam, Commvault, or Windows Server Backup) or archive tools (e.g., 7-Zip, WinRAR) may perform integrity checks or verify digital signatures on backup files or archived software packages during scheduled maintenance windows. These jobs often run as system services or scheduled