tElock 099 additional

Hunt Hypothesis

This hypothesis targets the presence of tElock ransomware variants, which typically encrypt files and demand payment, indicating a potential active breach or staging phase in the environment. Proactively hunting for this signature allows the SOC to identify compromised hosts early, minimizing the blast radius and enabling rapid isolation before the encryption process completes.

YARA Rule

rule tElock_099_additional: PEiD
{
    strings:
        $a = { E9 5E DF FF FF 00 00 00 ?? ?? ?? ?? E5 ?? ?? 00 00 00 00 00 00 00 00 00 05 ?? ?? 00 F5 ?? ?? 00 ED ?? ?? 00 00 00 00 00 00 00 00 00 12 ?? ?? 00 FD ?? ?? 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 1D ?? ?? 00 00 00 00 00 30 ?? ?? 00 00 }
    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 legacy Java-based application server (e.g., Tomcat or WebLogic) is performing a routine heap dump or memory profiling task using a custom agent that embeds a specific byte sequence in the java.lang.management package. This can trigger the YARA rule if the rule targets specific class file structures or constant pool entries common in older JDK versions.

  • Filter/Exclusion: Exclude processes named java.exe or jre.exe when the parent process is a known service host (e.g., services.exe or svchost.exe) and the file path resides under standard JDK installation directories (e.g., C:\Program Files\Java\ or C:\Program Files (x86)\Java\).

• Scenario: An enterprise backup solution (e.g., Veeam, Commvault, or Acronis) is creating a snapshot or differential backup of a virtual machine or physical host. During the deduplication or compression phase, the backup agent may write temporary files or memory-mapped regions that match the byte pattern defined in tElock_099_additional, particularly if the rule inspects file headers or specific data blocks.

  • Filter/Exclusion: Exclude processes associated with known backup agents (e.g., vssadmin.exe, wbadmin.exe, commvault_agent.exe, acronis_agent.exe) and exclude file paths containing keywords like \Backup\, \Snapshots\, or \Temp\ within the backup service directory.

• Scenario: A developer or system administrator is running a unit test suite or integration test for a custom .NET or C++ application that intentionally includes a test fixture or mock object with a specific binary signature (e.g., a test DLL or EXE compiled with a specific linker flag or embedded resource). This test artifact is executed in a controlled development or QA environment but