ExeLockerv10IonIce

Hunt Hypothesis

This detection identifies potential ExeLocker v10 ransomware activity by matching executable files against a specific YARA signature designed to catch known malicious patterns. Proactively hunting for this indicator in Azure Sentinel allows the SOC team to identify early-stage infections before encryption begins, enabling rapid containment and reducing overall recovery time.

YARA Rule

rule ExeLockerv10IonIce
{
      meta:
		author="malware-lu"
strings:
		$a0 = { E8 00 00 00 00 60 8B 6C 24 20 81 ED 05 00 00 00 3E 8F 85 6C 00 00 00 3E 8F 85 68 00 00 00 3E 8F 85 64 00 00 00 3E 8F 85 60 00 00 00 3E 8F 85 5C 00 00 00 3E 8F 85 58 00 00 00 3E 8F 85 54 00 00 }

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 ExeLockerv10IonIce detection rule, including suggested filters and exclusions:

• Scenario: Endpoint Protection Agent Self-Protection Updates

  • Context: The primary security agent (e.g., Microsoft Defender Antivirus or CrowdStrike Falcon) performs a scheduled definition update. During this process, the agent’s core executable (MsMpEng.exe or FalconService) may lock its own configuration files or inject code into memory to prevent tampering during the update cycle, mimicking the behavior of ExeLocker.
  • Suggested Filter: Create an exclusion rule that ignores alerts where the parent process is MsMpEng.exe, FalconService.exe, or WdAgent.exe and the file path resides within the agent’s installation directory (e.g., C:\Program Files\Microsoft Defender\).

• Scenario: Scheduled System Backup Jobs

  • Context: Enterprise backup solutions like Veeam Agent for Windows or Acronis Cyber Protect run nightly jobs that lock application executables to ensure data consistency before snapshotting. The locking mechanism used by these agents often triggers the YARA signature designed to detect ExeLocker’s specific file-locking behavior.
  • Suggested Filter: Exclude alerts generated during defined maintenance windows (e.g., 02:00–04:00 UTC) where the initiating process is VeeamAgent.exe or AcronisBackupService.exe, specifically when targeting system drives (C:) rather than user data directories.

• Scenario: Software Deployment via Configuration Management

  • Context: Tools such as Microsoft Endpoint Configuration Manager (SCCM/MECM) or Ansible execute software deployments that involve installing or patching applications. During the installation phase, these tools frequently lock .exe files to prevent modification conflicts while