PECompactv147v150

Hunt Hypothesis

This hunt detects potentially malicious or obfuscated executables that utilize specific PE (Portable Executable) compression signatures identified by the PECompactv147v150 YARA rule, which often indicate attempts to evade static analysis through code packing. A SOC team should proactively search for these instances in Azure Sentinel to uncover hidden threats that may bypass standard signature-based defenses and require deeper behavioral investigation before execution.

YARA Rule

rule PECompactv147v150
{
      meta:
		author="malware-lu"
strings:
		$a0 = { EB 06 68 [4] C3 9C 60 E8 02 [3] 33 C0 8B C4 83 C0 04 93 8B E3 8B 5B FC 81 EB 0F A0 40 ?? 87 DD 8B 85 A6 A0 40 ?? 01 85 03 A0 40 ?? 66 C7 85 ?? A0 40 ?? 90 90 01 85 9E A0 40 ?? BB 5B 12 }

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

Here are 3-5 specific false positive scenarios for the PECompactv147v150 detection rule, along with suggested filters and exclusions:

• Scenario: Automated Windows Update Deployment via SCCM/Intune

  • Context: During scheduled maintenance windows, System Center Configuration Manager (SCCM) or Microsoft Intune pushes cumulative updates. The deployment agent often extracts and executes compressed .msi or .cab packages that utilize PE compression techniques matching the v147/v150 signatures to reduce payload size before installation.
  • Suggested Filter/Exclusion: Create a whitelist exclusion for processes spawned by ccmsetup.exe, CcmExec.exe, and Microsoft.IntuneManagementExtension.exe. Additionally, exclude file paths located within the C:\Windows\SoftwareDistribution\Download directory during business hours (08:00–18:00).

• Scenario: Antivirus Real-Time Scanning of Compressed Archives

  • Context: Enterprise Endpoint Detection and Response (EDR) agents, such as CrowdStrike Falcon or Microsoft Defender for Endpoint, perform real-time scanning on large compressed archives (e.g., .7z, .zip) downloaded by users. When the agent extracts these files in memory to scan them, it may trigger the PECompact rule due to the internal structure of the archive’s executable components.
  • Suggested Filter/Exclusion: Configure a behavioral exclusion for the specific EDR process (e.g., FalconSensor.exe or MsMpEng.exe) when the parent process is explorer.exe and the file extension is .zip, .7z, or .rar. Exclude events where the file size exceeds 50MB to filter out large archive extractions.

• Scenario: Database Backup Jobs Using Compressed Executables *