PELockNTv201

Hunt Hypothesis

This detection identifies potential PELock malware activity by matching file artifacts against a specific YARA signature designed to catch known variants in the environment. Proactive hunting for this behavior is essential to uncover early-stage infections that may evade standard signature-based alerts, allowing the SOC team to isolate affected assets before lateral movement occurs.

YARA Rule

rule PELockNTv201
{
      meta:
		author="malware-lu"
strings:
		$a0 = { EB 03 CD 20 EB EB 01 EB 1E EB 01 EB EB 02 CD 20 9C EB 03 CD }

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 PELockNTv201 detection rule, along with suggested filters and exclusions:

• Scenario: Antivirus Real-Time Scanning of Locked Executables

  • Context: Enterprise Endpoint Protection agents (e.g., Microsoft Defender Antivirus or CrowdStrike Falcon) frequently attempt to scan or update definitions for executables that are currently locked by another process. When the AV engine tries to access a file handle held by svchost.exe or a database service, it may trigger the PELockNTv201 signature due to concurrent file locking mechanisms.
  • Suggested Filter/Exclusion: Exclude processes belonging to known security vendors from triggering this rule. Add an exclusion for process names matching MsMpEng.exe, C-Service.exe, and csagent.exe when the target file path contains \Program Files\Microsoft Defender\.

• Scenario: Scheduled Backup Jobs Locking System Directories

  • Context: Automated backup solutions like Veeam Agent for Windows or Commvault execute nightly jobs that lock critical system directories (e.g., C:\Windows\System32 or application data folders) while performing incremental backups. The detection logic may interpret the file locking behavior during these high-I/O windows as a potential PELockNTv201 anomaly.
  • Suggested Filter/Exclusion: Implement a time-based exclusion window for backup agents. Configure the rule to suppress alerts generated by VeeamAgent.exe or ctagent.exe between 01:00 and 05:00 local server time, provided the source file path matches standard backup repository locations (e.g., C:\BackupData\).

• Scenario: Windows Update Service Modifying Locked DLLs

  • Context: The Windows Update service (`w