WWPACKv305c4ExtractableVirusShield

Hunt Hypothesis

This detection identifies potential malware extraction activities where adversaries utilize the WWPACK v305c4 packing mechanism to conceal malicious payloads within executable archives. Proactive hunting for this signature in Azure Sentinel is essential to uncover early-stage infection vectors that may evade standard heuristic scans, allowing the SOC team to isolate compromised assets before lateral movement occurs.

YARA Rule

rule WWPACKv305c4ExtractableVirusShield
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 03 05 40 1A B8 [2] 8C CA 03 D0 8C C9 81 C1 [2] 51 B9 [2] 51 06 06 B1 ?? 51 8C D3 }

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 5 specific false positive scenarios for the WWPACKv305c4ExtractableVirusShield rule, including suggested filters and exclusions:

• Scenario: Microsoft Office Click-to-Run Updates

  • Context: The Microsoft Office Click-to-Run service (OfficeClickToRun.exe) periodically downloads and extracts update packages containing embedded archives (.msi, .cab, or nested .zip files) that match the rule’s extractable virus signature. This often occurs during off-hours when the update agent runs automatically.
  • Suggested Filter/Exclusion: Exclude processes where ProcessName equals OfficeClickToRun.exe and CommandLine contains “Update” or “Download”. Alternatively, add a path exclusion for %ProgramFiles%\Common Files\Microsoft Shared\ClickToRun.

• Scenario: SCCM (Configuration Manager) Software Deployment

  • Context: During scheduled application deployments, the System Center Configuration Manager client (ccmexec.exe) extracts installation packages from .msi or .appx bundles. These packages often contain nested archives that trigger the ExtractableVirusShield logic as they are unpacked into temporary directories (e.g., C:\Windows\CCMCache).
  • Suggested Filter/Exclusion: Create an exclusion for the process ccmexec.exe when the file path starts with C:\Windows\CCMCache\. Additionally, filter out events where the parent process is smss.exe or svchost.exe running under the “System” user context during deployment windows.

• Scenario: Antivirus Engine Real-Time Scanning of Archive Repositories

  • Context: Enterprise antivirus solutions (e.g., CrowdStrike Falcon, Symantec Endpoint Protection) perform real-time scanning on large archive repositories used by backup agents or document management