tElock v098 additional

Hunt Hypothesis

This rule identifies specific variants of the tElock ransomware family, indicating potential encryption or data exfiltration activities within the environment. Proactively hunting for these signatures in Azure Sentinel allows the SOC to detect low-severity ransomware strains that may evade standard behavioral detections, enabling early containment before widespread encryption occurs.

YARA Rule

rule tElock_v098_additional: PEiD
{
    strings:
        $a = { E9 25 E4 FF FF 00 00 00 ?? ?? ?? ?? 1E }
    condition:
        $a 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 DevOps engineer runs a custom Python script using the pycryptodome library to encrypt sensitive configuration files before archiving them to Azure Blob Storage. The script imports specific cryptographic primitives and executes a loop structure that matches the heuristic pattern of the tElock_v098_additional rule, triggering a detection on the python.exe process.

  • Filter/Exclusion: Exclude detections where the parent process is python.exe or python3.exe and the command line contains keywords like encrypt, archive, or backup, specifically if the working directory is within a designated C:\DevOps\Scripts or C:\Tools\Crypto path.

• Scenario: The enterprise endpoint protection agent (e.g., CrowdStrike Falcon or SentinelOne) performs a scheduled integrity check on its own rule set or configuration files. During this self-test, it loads a YARA rule file into memory and executes a verification routine that mimics the execution flow of the tElock variant, causing the rule to match its own scanning process.

  • Filter/Exclusion: Exclude detections where the process name is falconctl.exe, sentineloneagent.exe, or edr_agent.exe and the file path resides in the vendor’s installation directory (e.g., C:\Program Files\CrowdStrike\ or C:\Program Files\SentinelOne\).

• Scenario: A database administrator uses a third-party tool like pgAdmin or SQL Server Management Studio (SSMS) to execute a stored procedure that performs data masking or encryption on a test database. The tool spawns a helper process that loads a shared library containing cryptographic functions, which the YARA rule interprets as the tElock payload due to overlapping function signatures.

  • Filter/Exclusion: Exclude detections where the parent process is `ss