tElockv085f

Hunt Hypothesis

This hunt hypothesis targets adversaries leveraging specific file-based indicators defined by the tElockv085f YARA signature to identify potentially malicious artifacts within the environment. Proactively hunting for this behavior in Azure Sentinel is essential to detect low-severity threats that may evade standard alerting thresholds, ensuring early visibility into emerging file-centric attack patterns before they escalate.

YARA Rule

rule tElockv085f
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 60 E8 02 00 00 00 CD 20 E8 00 00 00 00 5E 2B C9 58 74 02 }

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 tElockv085f detection rule, including suggested filters and exclusions tailored for an enterprise environment:

• Scenario: Automated Endpoint Protection Scans

  • Context: The YARA rule triggers when CrowdStrike Falcon or Microsoft Defender for Endpoint performs a scheduled deep scan of the C:\ProgramData directory. During these scans, the protection engine spawns temporary worker processes that match the signature logic of the rule while analyzing locked files.
  • Suggested Filter/Exclusion: Create an exclusion based on process lineage. Exclude alerts where the parent process is falcon.sysmon.exe (CrowdStrike) or MsMpEng.exe (Defender) and the file path contains \ProgramData\. Alternatively, add a filter to suppress alerts occurring during known maintenance windows (e.g., 02:00–04:00 UTC).

• Scenario: Enterprise Backup Agent Operations

  • Context: The rule fires when Veeam Backup & Replication or Rubrik agents initiate a backup job. These agents often lock and read large database files (e.g., .vmdk or .bak) simultaneously, mimicking the behavior pattern that tElockv085f is designed to detect as suspicious locking activity.
  • Suggested Filter/Exclusion: Implement a process-based exclusion for known backup service executables such as Veeam.Backup.Service.exe, rubrik-agent.exe, or CommServe.exe. Additionally, exclude file paths matching the pattern \\BackupServer\Share\ to prevent noise from network-mounted backup repositories.

• Scenario: Scheduled Group Policy Updates

  • Context: During user logon or scheduled policy refresh cycles (typically every 90 minutes),