tElock099tE

Hunt Hypothesis

This hunt hypothesis targets adversaries executing custom malware or scripts identified by the specific YARA signature “tElock099tE,” which may indicate early-stage reconnaissance or lateral movement activities often missed by standard alerts. Proactively hunting for this behavior in Azure Sentinel allows the SOC team to validate low-severity detections against broader telemetry, ensuring that subtle indicators of compromise are not overlooked before they escalate into significant incidents.

YARA Rule

rule tElock099tE
{
      meta:
		author="malware-lu"
strings:
		$a0 = { E9 5E DF FF FF 00 00 00 [4] E5 [2] 00 00 00 00 00 00 00 00 00 05 }

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 5 specific false positive scenarios for the tElock099tE detection rule, including suggested filters and exclusions:

• Scenario: Automated Antivirus Definition Updates via Microsoft Defender

  • Context: The YARA rule flags the MsMpEng.exe process when it downloads and installs new virus definition updates during business hours. This often triggers file creation or memory injection events that mimic the rule’s signature for suspicious behavior.
  • Filter/Exclusion: Exclude processes where ImageName equals MsMpEng.exe AND CommandLine contains “UpdateService”. Alternatively, create a filter to ignore alerts originating from the specific service account NT SERVICE\MsMpSvc.

• Scenario: Scheduled Database Backup Jobs using Veeam or SQL Server Agent

  • Context: During nightly maintenance windows (e.g., 2:00 AM – 4:00 AM), backup agents like Veeam Transport Service or SQL Server Agent generate high-volume I/O and spawn child processes that match the tElock099tE signature, particularly when compressing large transaction logs.
  • Filter/Exclusion: Implement a time-based exclusion for alerts occurring between 01:00 and 05:00 on weekdays where ProcessName is VeeamTransport.exe or sqlagent.exe. Additionally, exclude file paths located within the dedicated backup directory (e.g., \Backup\).

• Scenario: Enterprise Software Deployment via Microsoft Endpoint Configuration Manager (SCCM)

  • Context: When SCCM pushes a new application package to endpoints, the CCMExec.exe process initiates installation scripts that modify system files and registry keys. The YARA rule may misinterpret these legitimate script executions as potential lateral movement or unauthorized code execution.
  • **Filter