ASPackv10803AlexeySolodovnikov

Hunt Hypothesis

This hypothesis targets the presence of ASPack-packed executables, a common obfuscation technique used by adversaries to compress malware and evade static analysis. Proactively hunting for this signature in Azure Sentinel allows the SOC team to identify potentially compromised endpoints or suspicious artifacts that may be hiding malicious payloads within standard file formats.

YARA Rule

rule ASPackv10803AlexeySolodovnikov
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 60 E8 00 00 00 00 5D 81 ED 0A 4A 44 00 BB 04 4A 44 00 03 DD }
	$a1 = { 60 E8 00 00 00 00 5D 81 ED 0A 4A 44 00 BB 04 4A 44 00 03 DD 2B 9D B1 50 44 00 83 BD AC 50 44 00 00 89 9D BB 4E }
	$a2 = { 60 E8 00 00 00 00 5D [6] BB [4] 03 DD }
	$a3 = { 60 E8 00 00 00 00 5D [6] BB [4] 03 DD 2B 9D B1 50 44 00 83 BD AC 50 44 00 00 89 9D BB 4E }

condition:
		$a0 at pe.entry_point or $a1 at pe.entry_point or $a2 at pe.entry_point or $a3 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 4 string patterns in its detection logic.

• Source Rule

False Positive Guidance

• Scenario: A developer or DevOps engineer runs a custom build script that uses the ASPack packer (specifically version 1.08.03) to compress and protect a proprietary C++ application binary before deployment to staging environments.

  • Filter/Exclusion: Exclude files located in specific build artifact directories (e.g., C:\Builds\Output\, D:\Artifacts\) or exclude processes where the parent is a known build tool (e.g., msbuild.exe, dotnet.exe, cmake.exe).

• Scenario: An IT administrator installs a legacy internal utility or a third-party monitoring agent that was compiled and packed with ASPack to reduce file size and protect IP, placing the executable in a standard system or vendor directory.

  • Filter/Exclusion: Exclude files residing in vendor-specific directories (e.g., C:\Program Files\VendorName\, C:\Program Files (x86)\InternalTools\) or exclude files with a valid digital signature from the internal CA or known vendor.

• Scenario: A scheduled maintenance job (e.g., via Task Scheduler or cron) executes a small, packed helper script or binary used for log rotation or disk cleanup that was packed with ASPack to avoid antivirus interference during the execution window.

  • Filter/Exclusion: Exclude processes where the parent is schtasks.exe or taskeng.exe and the file path contains keywords like maintenance, cleanup, or logs, or exclude files in C:\Windows\Temp\ or C:\ProgramData\Maintenance\ if the rule is scoped to specific directories.

• Scenario: A QA engineer runs a test harness that dynamically generates and packs a small test executable with ASPack to verify compression integrity or performance metrics in a lab environment.

  • **Filter/