EXELOCK66615

Hunt Hypothesis

This detection identifies potential malicious executable activity by leveraging a specific YARA signature to flag known threat patterns within the environment. Proactive hunting for this indicator in Azure Sentinel is essential to uncover early-stage compromises that may evade standard rule-based alerts due to their low severity classification.

YARA Rule

rule EXELOCK66615
{
      meta:
		author="malware-lu"
strings:
		$a0 = { BA [2] BF [2] EB ?? EA [4] 79 ?? 7F ?? 7E ?? 1C ?? 48 78 ?? E3 ?? 45 14 ?? 5A E9 }

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 EXELOCK66615 detection rule, including suggested filters and exclusions tailored for an enterprise environment:

• Scenario: Antivirus Real-Time Scanning of Executables

  • Context: Enterprise Endpoint Protection suites (e.g., Microsoft Defender for Endpoint, CrowdStrike Falcon) frequently lock executable files in the C:\Program Files directory while performing real-time signature scans or heuristic analysis. This locking mechanism can trigger the rule if it interprets the file handle acquisition as a suspicious “locking” event on a critical binary.
  • Filter/Exclusion: Exclude processes where the parent process is the AV engine service (e.g., MsMpEng.exe, C:\Program Files\CrowdStrike\fs_qc_service.exe) and the target file path contains \Program Files\.

• Scenario: Scheduled Software Deployment via SCCM/Intune

  • Context: During off-hours, System Center Configuration Manager (SCCM) or Microsoft Intune agents push application updates. The deployment agent (ccmsetup.exe or Microsoft.IntuneManagementAgent) often locks the target .exe file to prevent modification during installation or patching, mimicking the behavior of a malicious lock-down mechanism.
  • Filter/Exclusion: Create an exclusion for events occurring between 01:00 and 05:00 local time where the initiating process is ccmsetup.exe, Microsoft.IntuneManagementAgent.exe, or WuaUla.exe (Windows Update).

• Scenario: Database Backup and Maintenance Jobs

  • Context: SQL Server maintenance jobs often lock database engine executables (sqlservr.exe) to ensure data consistency during backup routines. If the YARA rule monitors file system locks on database binaries, these routine operations will generate