ASPackv211cAlexeySolodovnikov

Hunt Hypothesis

This hunt hypothesis targets the execution of files packed with the ASPack v2.11 compressor, a technique frequently employed by adversaries to obfuscate malicious payloads and evade static analysis. Proactively hunting for this signature in Azure Sentinel is essential because low-severity detections often serve as early indicators of advanced threats that may bypass traditional antivirus solutions due to their compressed structure.

YARA Rule

rule ASPackv211cAlexeySolodovnikov
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 60 E8 02 00 00 00 EB 09 5D 55 81 ED 39 39 44 00 C3 E9 59 04 00 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

Here are 3-5 specific false positive scenarios for the ASPackv211cAlexeySolodovnikov YARA rule, which typically detects ASPack-packed executables often associated with software obfuscation or compression. In an enterprise environment, legitimate applications frequently use this packing technique to reduce file size and protect intellectual property.

• Scenario: Deployment of Microsoft Office Updates via SCCM/Intune

  • Context: The System Center Configuration Manager (SCCM) or Microsoft Intune agent regularly downloads and installs cumulative updates for the Microsoft Office suite (e.g., OfficeC2RClient.exe or Setup.exe). These installers are frequently packed using ASPack to optimize bandwidth usage during distribution.
  • Filter/Exclusion: Create a path-based exclusion for the standard installation directory: C:\Program Files\Microsoft Office\root\Office16\*. Additionally, exclude processes spawned by ccmsetup.exe (SCCM) and IntuneManagementExtension.exe when they execute files within this scope.

• Scenario: Execution of Antivirus Definition Updates

  • Context: Enterprise-grade security suites like CrowdStrike Falcon, SentinelOne, or Symantec Endpoint Protection periodically download and install new definition databases. The updater executables (e.g., CnsUpdate.exe for CrowdStrike) often utilize ASPack compression to ensure rapid deployment across the network without consuming excessive storage on endpoints.
  • Filter/Exclusion: Exclude the specific vendor update service paths, such as C:\Program Files\CrowdStrike\Falcon\* or C:\ProgramData\Symantec\Symantec Endpoint Protection\*.exe. Implement a process parent filter to only flag alerts where the parent process is not the known AV updater (e.g., exclude if Parent Process Name contains “Falcon