XCR v012 X Lock

Hunt Hypothesis

This rule detects the presence of XCR v012 X Lock, a specific variant of the XCR ransomware family, indicating that an adversary has deployed or is preparing to execute a ransomware payload on a host. Proactively hunting for this signature in Azure Sentinel allows the SOC team to identify early-stage ransomware activity or dormant payloads before encryption begins, enabling rapid containment and reducing the potential impact on critical workloads.

YARA Rule

rule XCR_v012_X_Lock: PEiD
{
    strings:
        $a = { 60 9C E8 00 00 00 00 8B DD 5D 81 ED ?? ?? ?? ?? 89 9D }
    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 security team deploys a custom PowerShell script to enforce “BitLocker” or “XLock” (a proprietary or internal naming convention for a locking mechanism) on endpoints during a patching cycle. The script writes a specific marker file or registry key that matches the YARA signature for XCR_v012_X_Lock.

  • Filter/Exclusion: Exclude events where the process name is powershell.exe or pwsh.exe and the command line contains Set-BitLocker or references the specific internal script path (e.g., C:\Scripts\LockEndpoints.ps1).

• Scenario: An IT administrator uses a third-party endpoint management tool (such as SCCM, Intune, or a custom agent) to execute a maintenance task that temporarily locks user sessions or applies a “maintenance mode” flag. This action may create a temporary lock file or modify a specific registry key that triggers the YARA rule.

  • Filter/Exclusion: Exclude events originating from known service accounts (e.g., svc-sccm, intune-agent) or processes like CcmExec.exe or IntuneAgent.exe when the action is associated with a scheduled maintenance window.

• Scenario: A developer or QA engineer runs a local test harness or automation script that simulates a “lock” state for an application under test. The script creates a dummy lock file or sets a specific environment variable that matches the YARA pattern.

  • Filter/Exclusion: Exclude events where the user is part of the DevTeam or QA group and the working directory is within a known development folder (e.g., C:\Users\dev\projects\ or C:\QA\testruns\).

• Scenario: A backup solution (e.g., Veeam, Commvault, or Acron