IMPostorPack10MahdiHezavehi

Hunt Hypothesis

This YARA rule targets the IMPostorPack10 malware variant, which is often used for credential theft and remote access, indicating potential compromise of user sessions or sensitive data exfiltration. Proactively hunting for this signature in Azure Sentinel allows the SOC to identify low-severity infections early, preventing lateral movement or persistence before they escalate into more impactful breaches.

YARA Rule

rule IMPostorPack10MahdiHezavehi
{
      meta:
		author="malware-lu"
strings:
		$a0 = { BE [3] 00 83 C6 01 FF E6 00 00 00 00 [2] 00 00 00 00 00 00 00 00 00 [3] 00 ?? 02 [2] 00 10 00 00 00 02 00 }

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 a legitimate, open-source Python packaging tool or a custom internal utility that shares the same structural metadata or string signatures as the IMPostorPack10 family (often associated with specific malware packers or obfuscation techniques). For instance, if the YARA rule matches on specific byte sequences or string patterns found in a custom-built installer script for an internal application.

  • Filter/Exclusion: Exclude files located in specific development or build directories (e.g., C:\Projects\InternalApp\build\, C:\src\) or exclude files owned by known service accounts used for CI/CD pipelines (e.g., svc-ci-cd, build-agent).

• Scenario: A third-party vendor application or plugin (e.g., a specific version of a monitoring agent, a legacy Java-based tool, or a custom .NET assembly) that was compiled with a specific obfuscator or packer that coincidentally matches the YARA signature. This is common with older or niche enterprise software that hasn’t been updated in years.

  • Filter/Exclusion: Create an allowlist for specific executable paths or file hashes associated with known vendor software (e.g., C:\Program Files\VendorApp\bin\agent.exe, C:\Tools\LegacyTool\lib\plugin.dll). Alternatively, exclude processes started by known vendor service names (e.g., VendorSvc.exe).

• Scenario: A scheduled maintenance job or a backup utility that temporarily creates a packed or compressed archive file in a temp directory, which the YARA rule identifies as a potential imposter packer due to its file structure or embedded strings. This often happens with tools like 7-Zip, WinRAR, or custom backup scripts that create intermediate files.

  • Filter/Exclusion: Exclude files in standard temporary directories (e.g.,