WWPACKv305c4Modified

Hunt Hypothesis

This detection identifies adversaries who have modified the WWPACKv305c4 component to potentially inject malicious code or evade signature-based security controls within the Windows ecosystem. Proactively hunting for this anomaly in Azure Sentinel is critical because low-severity modifications often serve as early indicators of stealthy persistence mechanisms that could escalate into significant compromises if left uninvestigated.

YARA Rule

rule WWPACKv305c4Modified
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 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 4 specific false positive scenarios for the WWPACKv305c4Modified detection rule, including suggested filters and exclusions:

• Scenario: Microsoft Office Click-to-Run Self-Update Service

  • Context: The OfficeClickToRun.exe process frequently modifies the WWPACK (Windows Package) cache files in %ProgramFiles%\Microsoft Office\root\Office16 during background updates or feature installations. This triggers the rule when the service writes to the package manifest or content directories.
  • Filter/Exclusion: Exclude processes where ImageFileName matches OfficeClickToRun.exe and CommandLine contains /update. Alternatively, add a path exclusion for %ProgramFiles%\Microsoft Office\root\Office16\*.wwpack.

• Scenario: SCCM (Configuration Manager) Application Deployment

  • Context: During scheduled application deployments or software updates via Microsoft Endpoint Configuration Manager (SCCM), the ccmsetup.exe or WUAHandler.exe processes modify WWPACK files to stage new applications. This often occurs during maintenance windows on domain-joined workstations.
  • Filter/Exclusion: Create a rule exception for process names ccmsetup.exe, WUAHandler.exe, and AppVClient.exe. Additionally, exclude file paths located within the SCCM cache directory: %ProgramData%\Microsoft\CCMCache\*.wwpack.

• Scenario: Antivirus Engine Real-Time Scanning

  • Context: Enterprise EDR solutions (e.g., CrowdStrike Falcon, Microsoft Defender for Endpoint) perform real-time scanning and quarantine operations. When the AV engine scans or updates its own definition packages stored in WWPACK format, it may trigger a “modification” event on the file itself.
  • Filter/Exclusion: Exclude events where `ParentProcessName