ASProtectvxx

Hunt Hypothesis

This rule identifies the presence of ASProtect-packed executables, a technique frequently employed by adversaries to obfuscate malicious payloads and evade static analysis. Proactively hunting for these signatures in Azure Sentinel allows the SOC to uncover hidden threats in email attachments or endpoint downloads that may bypass traditional signature-based detections.

YARA Rule

rule ASProtectvxx
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 60 [5] 90 5D [11] 03 DD }

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: Administrators updating or deploying older, un-recompiled business applications (e.g., legacy ERP modules or proprietary point-of-sale software) that were packed with ASProtect to reduce binary size or protect intellectual property.
  • Filter/Exclusion: Create a whitelist for specific executable paths or hashes associated with known legacy applications (e.g., C:\Program Files\LegacyERP\bin\app.exe) and exclude them from YARA scanning if their version number matches the known packed build.
• Third-Party Vendor Updates: Automated scheduled jobs or manual installations of third-party vendor tools (e.g., specific versions of antivirus agents, database backup utilities, or monitoring agents) that utilize ASProtect for code obfuscation during the build process.
  • Filter/Exclusion: Exclude executables located in standard vendor installation directories (e.g., C:\Program Files\VendorName\) that are signed by the vendor’s trusted code-signing certificate, or add specific SHA-256 hashes of the vendor’s packed binaries to the exclusion list.
• Development and Testing Environments: Developers or QA engineers running local builds of internal applications or testing third-party libraries in non-production environments where ASProtect is used for debugging or size optimization.
  • Filter/Exclusion: Exclude processes or files originating from development-specific directories (e.g., C:\Users\<dev_user>\Projects\ or C:\Temp\builds\) and limit the detection rule to production and user-facing endpoints, or exclude processes spawned by known IDEs (e.g., devenv.exe, code.exe).
• Backup and Archive Restoration: Restoration of old backup files or archives (e.g., from Veeam, Commvault, or Windows Shadow Copies) onto endpoints where the original binaries were packed with ASProtect years ago and have not been recompiled. *