ASPackv10804AlexeySolodovnikov

Hunt Hypothesis

This hypothesis targets the presence of ASPack-packed executables, a common obfuscation technique used by adversaries to hide malicious payloads and evade static analysis. Proactively hunting for these signatures in Azure Sentinel helps identify low-severity but potentially stealthy threats that may be leveraging packing to bypass initial detection controls.

YARA Rule

rule ASPackv10804AlexeySolodovnikov
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 60 E8 41 06 00 00 EB 41 }

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

• Legacy Application Maintenance: An IT administrator manually updates a legacy line-of-business application (e.g., a custom Java or .NET wrapper) that was originally packed with ASPack to reduce file size and protect IP. The update process involves compiling the source code and re-packing the executable using the ASPack.exe tool or a build script that invokes it, triggering the YARA signature on the newly generated binary.

  • Filter/Exclusion: Exclude files located in specific legacy application directories (e.g., C:\Apps\LegacyERP\bin\) or exclude processes where the parent is a known build tool (e.g., msbuild.exe, javac.exe) and the target file path contains version control markers (e.g., build, dist, release).

• Third-Party Installer Customization: A software vendor provides a custom installer for a niche enterprise tool (e.g., a specialized CAD plugin or financial reporting suite) that uses ASPack to compress the payload. When the IT team deploys this via SCCM or Intune, the installer executable or its embedded payload matches the signature during the deployment scan.

  • Filter/Exclusion: Whitelist known vendor-specific executable names (e.g., VendorToolSetup.exe) or exclude files with specific digital signatures from trusted vendors (e.g., VendorName, Inc.) if the YARA rule allows for signature-based exclusion, or exclude paths under standard installer directories (e.g., C:\Program Files (x86)\VendorName\).

• Backup and Archiving of Packed Binaries: A scheduled backup job (e.g., Veeam, Commvault, or native Windows Server Backup) copies or restores a large archive containing legacy packed executables. During the restore or verification phase, the backup agent reads the packed binaries into memory or temporary files, triggering the detection on the restored or staged files