VXTibsZhelatinStormWormvariant

Hunt Hypothesis

This hunt hypothesis targets adversaries executing the Zhelatin Storm worm variant to identify early-stage file system infections and lateral movement patterns within the Azure environment. Proactively hunting for this low-severity indicator allows the SOC team to detect dormant or initial infection stages before they escalate into widespread data exfiltration or network disruption events.

YARA Rule

rule VXTibsZhelatinStormWormvariant
{
      meta:
		author="malware-lu"
strings:
		$a0 = { FF 74 24 1C 58 8D 80 [2] 77 04 50 68 62 34 35 04 E8 }

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 VXTibsZhelatinStormWormvariant detection rule, including suggested filters and exclusions tailored for an enterprise environment:

• Scenario: Antivirus Engine Self-Scanning or Update Deployment

  • Context: Enterprise endpoint protection suites like CrowdStrike Falcon, SentinelOne, or Microsoft Defender for Endpoint often spawn multiple worker processes to scan their own installation directories or download definition updates. The YARA rule may misidentify the high-volume file creation and memory injection patterns of these internal agents as worm-like behavior, particularly when the VXTibs signature overlaps with the agent’s update module hash.
  • Suggested Filter/Exclusion: Exclude processes where the parent process name matches known EDR agents (e.g., FalconSensor.exe, SentinelOneAgent.exe, MsMpEng.exe) and the file path resides within the vendor’s installation directory (e.g., C:\Program Files\CrowdStrike\ or C:\Windows\System32).

• Scenario: Scheduled System Maintenance via PowerShell or Task Scheduler

  • Context: IT administrators frequently deploy scheduled maintenance jobs using Task Scheduler to run cleanup scripts, log rotation, or configuration backups. A script utilizing PowerShell (powershell.exe) to iterate through large directories and generate temporary files can trigger the “Storm” variant logic due to rapid file I/O and process spawning that mimics worm propagation.
  • Suggested Filter/Exclusion: Create an exclusion for events where the parent process is TaskSchedulerService.exe or svchost.exe (with service name Schedule) AND the command line contains specific keywords like “maintenance,” “cleanup,” or “backup.” Additionally, exclude execution paths under C:\Windows\System32\Tasks\.

• **Scenario: Software Deployment