VxHeloween1172

Hunt Hypothesis

This hunt hypothesis targets the execution of specific malware signatures identified by the VxHeloween1172 YARA rule to detect early-stage adversary activity that may evade standard signature-based detection. Proactively hunting for this behavior in Azure Sentinel allows the SOC team to validate low-severity alerts against broader telemetry, ensuring potential threats are not overlooked before they escalate into significant incidents.

YARA Rule

rule VxHeloween1172
{
      meta:
		author="malware-lu"
strings:
		$a0 = { E8 [2] 5E 81 EE [2] 56 50 06 0E 1F 8C C0 01 [2] 01 [2] 80 [4] 8B [2] A3 [2] 8A [2] A2 [2] B8 [2] CD 21 3D }

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 VxHeloween1172 detection rule, including suggested filters and exclusions:

• Antivirus Engine Real-Time Scanning

  • Scenario: The primary endpoint protection agent (e.g., Microsoft Defender Antivirus or CrowdStrike Falcon) performs a real-time scan on a large user document repository. During the scan, the engine spawns multiple child processes to analyze file signatures, which matches the YARA pattern for suspicious process spawning behavior defined in VxHeloween1172.
  • Filter/Exclusion: Exclude processes where the parent executable path contains \Program Files\Microsoft Defender\ or \CrowdStrike\FalconAgent\, and specifically filter out process names ending in MsMpEng.exe or CsFalconService.exe.

• Scheduled System Backup Jobs

  • Scenario: A nightly scheduled task triggers a backup utility (e.g., Veeam Agent for Windows or Acronis Cyber Protect) to compress and archive user data. The backup engine launches temporary worker processes with high I/O activity that mimic the file manipulation signatures detected by the rule.
  • Filter/Exclusion: Create an exclusion based on the Scheduled Task Name containing keywords like “Backup”, “Veeam”, or “Acronis”. Additionally, filter out events occurring during the defined maintenance window (e.g., 02:00 – 04:00 UTC) where these jobs are known to run.

• Software Deployment via Configuration Management

  • Scenario: An IT automation tool (such as SCCM/MECM, Ansible Tower, or Puppet) pushes a new application update to the domain. The deployment agent executes a script that installs binaries and modifies registry keys, triggering the rule’s logic regarding new executable creation in protected directories.

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