VxSYP

Hunt Hypothesis

This detection leverages a specialized YARA signature to identify the presence of specific malware or suspicious artifacts associated with the VxSYP indicator within Azure Sentinel workloads. Proactive hunting for this signal is essential to uncover early-stage threats that may evade standard heuristic defenses, allowing the SOC team to investigate potential lateral movement or data exfiltration before an incident escalates.

YARA Rule

rule VxSYP
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 47 8B C2 05 1E 00 52 8B D0 B8 02 3D CD 21 8B D8 5A }

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 VxSYP detection rule in an enterprise environment, along with targeted filtering strategies:

• Scenario: Antivirus Engine Self-Scanning

  • Context: The VxSYP signature often triggers when the endpoint protection agent (e.g., Microsoft Defender, CrowdStrike Falcon, or Symantec Endpoint Protection) scans its own installation directory or updates its definition database. The YARA rule may detect the specific binary structure of the AV engine itself as a potential anomaly during high-frequency scanning cycles.
  • Filter/Exclusion: Create an exclusion based on Process Name and File Path. Exclude processes matching MsMpEng.exe, FalconSensor.exe, or Symantec Endpoint Protection when accessing paths within their own installation directories (e.g., C:\Program Files\Microsoft Defender\).

• Scenario: Scheduled PowerShell Deployment Scripts

  • Context: IT Operations teams frequently run scheduled tasks using PowerShell to deploy configurations, patch software, or manage user profiles. If the VxSYP rule detects specific script execution patterns common in these automation jobs (e.g., powershell.exe loading a .ps1 file containing the signature pattern), it may flag legitimate administrative maintenance as suspicious activity.
  • Filter/Exclusion: Implement an exclusion for Process Name: powershell.exe where the Command Line contains specific keywords like -ExecutionPolicy Bypass or references to known internal script repositories (e.g., paths starting with \\fileserver\scripts\). Additionally, exclude events occurring during defined maintenance windows (e.g., 02:00–04:00 UTC).

• Scenario: Microsoft Office Background Services

  • Context: In environments where users have heavy document processing needs, background services like OfficeClickToRun.exe or `