ASPackv2000AlexeySolodovnikov

Hunt Hypothesis

This detection identifies potential malicious activity associated with the ASPack v2000 packer, which adversaries frequently employ to obfuscate executable files and evade traditional signature-based scanning. Proactively hunting for this behavior in Azure Sentinel is essential to uncover hidden threats that may bypass standard defenses by leveraging legacy packing techniques often found in sophisticated supply chain or fileless attacks.

YARA Rule

rule ASPackv2000AlexeySolodovnikov
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 60 E8 70 05 00 00 EB 4C }

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 ASPackv2000AlexeySolodovnikov detection rule, including targeted filters and exclusions:

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

  • Context: When System Center Configuration Manager (SCCM) or Microsoft Intune pushes cumulative updates for the Microsoft Office suite, the installer often utilizes ASPack to compress the payload. The YARA rule may flag these legitimate update executables as potential packers due to their high entropy and specific header signatures.
  • Filter/Exclusion: Create a whitelist exclusion based on the file path and publisher signature. Exclude files located in C:\Program Files\Microsoft Office\ or C:\Windows\SoftwareDistribution\Download\ where the digital signer is “Microsoft Corporation” and the file hash matches known update builds.

• Scenario: Execution of Antivirus Engine Updates

  • Context: Enterprise endpoint protection suites (e.g., CrowdStrike Falcon, Symantec Endpoint Protection, or McAfee) frequently download and install definition updates packaged with ASPack to reduce bandwidth usage during off-hours. The rule may trigger on the temporary unpacking process or the update agent itself.
  • Filter/Exclusion: Implement a filter that excludes processes running under specific service accounts (e.g., NT SERVICE\Symantec Endpoint Protection or SYSTEM) and restricts detection to file paths containing keywords like \Update, \Definitions, or \Content.

• Scenario: Scheduled Backup Jobs Using Veeam or Commvault

  • Context: During nightly backup windows, tools like Veeam Backup & Replication or Commvault SmartClient often spawn temporary helper processes that utilize ASPack for compression before archiving data. These background tasks generate high-entropy binaries that mimic the behavior of packed malware.