VxQuake518

Hunt Hypothesis

This detection identifies potential malware activity by leveraging the VxQuake518 YARA signature to scan for specific malicious patterns within file artifacts. A proactive hunt is essential in Azure Sentinel to uncover early-stage threats that may evade standard heuristic controls, allowing analysts to investigate low-severity indicators before they escalate into significant incidents.

YARA Rule

rule VxQuake518
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 1E 06 8C C8 8E D8 [7] B8 21 35 CD 21 81 }

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 VxQuake518 detection rule, documented with corresponding filters and exclusions:

• Scenario: Automated Antivirus Definition Updates

  • Context: The enterprise endpoint protection suite (e.g., CrowdStrike Falcon, Microsoft Defender for Endpoint) automatically downloads and installs new signature definitions during off-hours. These updates often involve unpacking compressed archives containing executable payloads that mimic the behavior of the VxQuake518 threat family.
  • Filter/Exclusion: Create a process exclusion for the specific update service executables (e.g., C:\Program Files\CrowdStrike\csfalcon.exe or MsMpEng.exe) and exclude file paths under the vendor’s installation directory from YARA scanning during the defined maintenance window (02:00 – 04:00 UTC).

• Scenario: Scheduled PowerShell Script Execution for Compliance Reporting

  • Context: A nightly compliance job runs a custom PowerShell script (ComplianceReport.ps1) that dynamically generates temporary executable wrappers to aggregate data from multiple departments. The YARA rule flags the generated wrapper binaries as suspicious due to their obfuscated structure, which resembles VxQuake518’s packing technique.
  • Filter/Exclusion: Implement a hash-based exclusion for the known good SHA-256 hashes of the ComplianceReport.ps1 script and its associated output directory (C:\Data\Reports\Temp). Additionally, add a rule condition to ignore alerts where the parent process is specifically powershell.exe running with the -ExecutionPolicy Bypass flag during business hours.

• Scenario: Deployment of Internal Line-of-Business (LOB) Applications via SCCM

  • Context: The IT team uses Microsoft Endpoint Configuration Manager (SCCM/MECM)