ILUCRYPTv4015exe

Hunt Hypothesis

This rule identifies the presence of the ILUCRYPT ransomware variant (version 4.0.15) on endpoints, indicating a potential active encryption threat or a dormant payload awaiting execution. Proactively hunting for this specific signature allows the SOC to isolate affected assets and verify remediation status before the adversary triggers the encryption process, thereby minimizing data loss and operational downtime.

YARA Rule

rule ILUCRYPTv4015exe
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 8B EC FA C7 46 F7 [2] 42 81 FA [2] 75 F9 FF 66 F7 }

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

• Scenario: A developer or DevOps engineer manually downloads the ILUCRYPTv4015.exe utility from the vendor’s official repository to perform a one-time bulk encryption of legacy data archives on a shared network drive.

  • Filter/Exclusion: Allow execution if the parent process is a known shell (e.g., cmd.exe, powershell.exe) initiated by a user in the DevOps or DataEngineering AD group, and the file path matches the designated tools directory (e.g., C:\Tools\ILUCRYPT\).

• Scenario: An automated scheduled task (e.g., DailyBackupEncryption) runs ILUCRYPTv4015.exe to encrypt nightly backup files before transferring them to the cloud storage bucket.

  • Filter/Exclusion: Exclude alerts where the parent process is Task Scheduler (svchost.exe with specific parameters or Taskeng.exe) and the command line contains the specific scheduled task name or the expected output directory (e.g., \\fileserver\backups\encrypted\).

• Scenario: A system administrator uses ILUCRYPTv4015.exe via a PowerShell script to rotate encryption keys for a specific application’s configuration files during a maintenance window.

  • Filter/Exclusion: Allow if the parent process is powershell.exe and the script path is located in the approved automation folder (e.g., C:\Scripts\Maintenance\), or if the user account belongs to the AppAdmins group and the execution occurs during the defined maintenance window (e.g., 02:00–04:00 UTC).

• Scenario: A CI/CD pipeline agent (e.g., Jenkins, Azure DevOps) executes ILUCRYPTv4015.exe as part of a build