ExeLocker10IonIce

Hunt Hypothesis

This detection identifies the presence of ExeLocker10IonIce ransomware signatures within executable files to uncover early-stage infection indicators that may not yet trigger high-severity alerts. Proactively hunting for this specific YARA rule in Azure Sentinel allows the SOC team to isolate potential threats before encryption begins, minimizing data loss and reducing incident response time.

YARA Rule

rule ExeLocker10IonIce
{
      meta:
		author="malware-lu"
strings:
		$a0 = { E8 00 00 00 00 60 8B 6C 24 20 81 ED 05 00 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 4 specific false positive scenarios for the ExeLocker10IonIce detection rule, including suggested filters and exclusions:

• Scenario: Scheduled Antivirus Definition Updates

  • Context: Enterprise endpoint protection suites (e.g., CrowdStrike Falcon, Microsoft Defender for Endpoint, or Symantec Endpoint Protection) often run automated definition update jobs during off-hours. These processes frequently spawn temporary executable wrappers that match the IonIce signature pattern while unpacking new signatures.
  • Filter/Exclusion: Create a rule exclusion based on the process image path and parent process name. Exclude any execution where ParentImage matches C:\Program Files\Microsoft Defender\MsMpEng.exe or C:\ProgramData\CrowdStrike\Falcon\Sensor\falconservice.exe.

• Scenario: Microsoft Office Click-to-Run Installation Service

  • Context: The Office Click-to-Run Service (OfficeClickToRun.exe) performs background maintenance, including feature updates and license validation. When it launches temporary installers or repair tools, the YARA rule may flag these legitimate executables as potential IonIce activity due to similar packing structures.
  • Filter/Exclusion: Add a process name exclusion for OfficeClickToRun.exe and its child processes (e.g., Setup.exe, OISCore.dll). Ensure the filter applies specifically when the execution occurs within the standard Office installation directory (C:\Program Files\Microsoft Office Root\...).

• Scenario: Automated Patch Deployment via SCCM/Intune

  • Context: During scheduled maintenance windows, tools like Microsoft Endpoint Configuration Manager (SCCM) or Intune Management Extension deploy patches. These agents often utilize a generic deployment engine that executes scripts and installers which mimic the behavior of ExeLocker10IonIce, triggering the alert