tElockv098

Hunt Hypothesis

This detection identifies potential file-based threats or specific malware signatures matching the tElockv098 YARA pattern within Azure Sentinel’s endpoint telemetry. Proactively hunting for this behavior allows the SOC team to uncover low-severity indicators that may represent early-stage attacks or known benign artifacts requiring validation before they escalate into critical incidents.

YARA Rule

rule tElockv098
{
      meta:
		author="malware-lu"
strings:
		$a0 = { E9 25 E4 FF FF 00 00 00 [4] 1E }

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

False Positive Scenarios for Rule tElockv098

• Scenario: Microsoft Defender Antivirus Scheduled Scan

  • Context: The daily automated scan performed by the Microsoft Defender service (MsMpEng.exe) often triggers this rule when scanning large directories containing encrypted archives or compressed software installers.
  • Filter/Exclusion: Add a process exclusion for C:\Program Files\Microsoft Defender\MsMpEng.exe within the YARA rule logic, specifically excluding matches where the parent process is svchost.exe running under the “DefenderSvc” service account.

• Scenario: SCCM (Configuration Manager) Software Deployment

  • Context: During enterprise-wide software deployments via Microsoft Endpoint Configuration Manager (MECM), the deployment agent (ccmexec.exe) extracts and installs packages that match the heuristic patterns of tElockv098, particularly when installing .NET-based applications.
  • Filter/Exclusion: Create a whitelist entry for the process path C:\Windows\CCM\ccmexec.exe and exclude alerts where the file extension is .msi or .cab located within the C:\ProgramData\Microsoft\CCM\Cache directory.

• Scenario: Veeam Backup & Replication Agent Activity

  • Context: The Veeam backup agent (VeeamBackupService.exe) frequently generates temporary lock files and encrypted snapshots during its nightly window, which mimic the signature behavior detected by tElockv098.
  • Filter/Exclusion: Implement a path-based exclusion for any file operations occurring under C:\Program Files\Veeam\Backup and Replication where the process name contains “Veeam” and the user context is NT SERVICE\VeeamTransportService.

• **Scenario: Adobe Acrobat Pro