PELockNTv204

Hunt Hypothesis

This detection identifies the presence of the PELockNTv204 malware variant through YARA signature matching, which often indicates early-stage infection or lateral movement within the environment. Proactively hunting for this rule in Azure Sentinel allows the SOC team to validate low-severity alerts before they escalate into critical incidents, ensuring rapid containment of potential threats that may evade standard heuristic-based detections.

YARA Rule

rule PELockNTv204
{
      meta:
		author="malware-lu"
strings:
		$a0 = { EB ?? CD [5] CD [5] EB ?? EB ?? EB ?? EB ?? CD [5] E8 [4] E9 [4] 50 C3 }

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 PELockNTv204 detection rule, including suggested filters and exclusions:

• Scenario: Microsoft Defender Antivirus Real-Time Scanning

  • Context: The MsMpEng.exe process frequently locks PE headers of executable files in the %ProgramFiles% directory during real-time scanning or on-demand updates to verify integrity. This often triggers PELockNTv204 when the rule detects the locking behavior as a potential fileless attack or unauthorized modification.
  • Filter/Exclusion: Exclude the process MsMpEng.exe (Microsoft Defender Antivirus) from triggering this rule when the target path contains \Program Files\WindowsApps\ or \Program Files\Microsoft Defender\.

• Scenario: SCCM Application Deployment and Configuration Manager

  • Context: During scheduled application deployments, the ccmsetup.exe or WuaHandler.exe processes lock PE headers of newly installed binaries to ensure version consistency before finalizing the installation. This is common in enterprise environments using Microsoft Endpoint Configuration Manager (MECM/SCCM).
  • Filter/Exclusion: Create an exclusion for process names starting with ccmsetup, WuaHandler, and AppVClient when they interact with files located within the %SystemDrive%\ProgramData\Microsoft\EndpointProtection\ directory.

• Scenario: Scheduled PowerShell Script for Patch Validation

  • Context: A nightly scheduled task runs a custom PowerShell script (PowerShell.exe) that iterates through critical system binaries to verify digital signatures and lock headers against tampering before the next maintenance window. The rule interprets this legitimate validation loop as an anomaly.
  • Filter/Exclusion: Exclude powershell.exe processes where the command line argument contains `-ExecutionPolicy Bypass -File “C:\Scripts