tElockv04xv05x

Hunt Hypothesis

This detection identifies potential file-based threats or specific malware signatures matching the tElockv04xv05x YARA pattern within the Azure Sentinel environment. Proactive hunting for this indicator is essential to uncover early-stage infections that may be missed by standard alerting, allowing the SOC team to investigate and contain low-severity anomalies before they escalate into broader incidents.

YARA Rule

rule tElockv04xv05x
{
      meta:
		author="malware-lu"
strings:
		$a0 = { C1 EE 00 66 8B C9 EB 01 EB 60 EB 01 EB 9C E8 00 00 00 00 5E 83 C6 ?? 8B FE 68 79 01 [2] 59 EB 01 }

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 3-5 specific false positive scenarios for the tElockv04xv05x detection rule in an enterprise environment, including suggested filters and exclusions:

• Scenario: Microsoft Defender Antivirus Real-Time Scanning on Temporary Files

  • Context: The YARA rule triggers when MsMpEng.exe (Microsoft Defender) scans temporary files created by user applications (e.g., .tmp, .docx drafts) in the %TEMP% directory. The signature matches a specific byte pattern often found in compressed archives or encrypted documents that Defender processes during real-time scanning.
  • Suggested Filter/Exclusion: Add an exclusion for the process MsMpEng.exe when operating on paths containing \AppData\Local\Temp\. Alternatively, configure the rule to ignore alerts where the parent process is explorer.exe or svchost.exe and the file extension is .tmp, .log, or .dmp.

• Scenario: Scheduled Office 365 ProPlus Update Tasks

  • Context: The Windows Task Scheduler executes the Microsoft Office Click-to-Run service (OfficeClickToRun.exe) during off-hours to apply cumulative updates. This process generates temporary installation manifests and XML configuration files that contain the specific signature pattern detected by tElockv04xv05x, causing a spike in alerts during maintenance windows (e.g., 2:00 AM – 4:00 AM).
  • Suggested Filter/Exclusion: Create a time-based exclusion for the rule between 01:00 and 06:00 local time. Additionally, exclude the process OfficeClickToRun.exe entirely from this detection if it is running under the context of the “System” or “Network Service” user account.

• **Scenario: Enterprise Backup