tElockv041x

Hunt Hypothesis

This YARA rule targets specific memory patterns or file signatures associated with the tElockv041x malware family, indicating potential low-severity intrusion or persistence mechanisms. Proactively hunting for this signature in Azure Sentinel allows the SOC team to identify early-stage infections or dormant payloads before they escalate to more impactful post-exploitation activities.

YARA Rule

rule tElockv041x
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 66 8B C0 8D 24 24 EB 01 EB 60 EB 01 EB 9C E8 00 00 00 00 5E 83 C6 50 8B FE 68 78 01 [2] 59 EB 01 EB AC 54 E8 03 [3] 5C EB 08 }

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 runs a local build script that invokes tElockv041x (a custom internal encryption/locking utility) to protect source code artifacts or temporary build outputs before archiving them. The process runs from a user’s home directory or a CI/CD agent workspace, triggering the YARA signature match on the binary or its generated lock file.

  • Filter/Exclusion: Exclude processes where the parent process is msbuild.exe, dotnet.exe, or npm.exe, and the working directory matches standard build paths (e.g., C:\Users\<user>\.nuget\, C:\builds\, or D:\src\). Additionally, exclude if the file extension is .tmp or .lock and the size is under 1MB.

• Scenario: An IT admin uses a PowerShell script to apply a temporary maintenance lock to a database file or configuration store during a planned upgrade window. The script executes tElockv041x directly from a shared admin tools folder (e.g., \\fileserver\tools\), which may not be in the standard application allowlist.

  • Filter/Exclusion: Allow execution if the parent process is powershell.exe or pwsh.exe and the command line contains keywords like -Lock, -Maintenance, or -Upgrade. Also, exclude if the file path resides in known admin tool directories (e.g., \\fileserver\tools\, C:\AdminTools\).

• Scenario: A scheduled task for nightly backup verification runs a custom validation tool that uses tElockv041x to ensure no writes occur during the integrity check. The task runs under the SYSTEM account from C:\Windows\System32\Tasks\ or a custom scripts folder, potentially bypassing