DMALocker4

Hunt Hypothesis

This detection identifies adversary behavior involving the execution of malicious binaries or scripts that match the specific signature defined by the DMALocker4 YARA rule. The SOC team should proactively hunt for this activity in Azure Sentinel to validate the effectiveness of the low-severity alert and uncover potential stealthy lateral movement or initial access attempts that may not yet trigger higher-priority thresholds.

YARA Rule

rule DMALocker4 : ransom {

    meta:
    Description = "Deteccion del ransomware DMA Locker version 4.0"
    ref = "https://blog.malwarebytes.org/threat-analysis/2016/02/dma-locker-a-new-ransomware-but-no-reason-to-panic/"
    Author = "SadFud"
    Date = "30/05/2016"
	Hash = "e3106005a0c026fc969b46c83ce9aeaee720df1bb17794768c6c9615f083d5d1"
    
    strings:
    $clave = { 21 44 4d 41 4c 4f 43 4b 34 2e 30 }
    
    condition:
    $clave 
    
}

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 DMALocker4 detection rule in an enterprise environment, including suggested filters and exclusions:

• Endpoint Protection Scanning of Locked Files

  • Scenario: The enterprise antivirus solution (e.g., CrowdStrike Falcon, Microsoft Defender for Endpoint) performs scheduled deep scans on critical system directories. During this process, the AV engine opens files with exclusive locks to verify integrity against known malware signatures, mimicking the behavior of a malicious locker.
  • Filter/Exclusion: Create an exclusion rule for processes running under the specific security vendor’s service accounts (e.g., C:\Program Files\CrowdStrike\csagent.exe) and filter out events where the parent process is the AV service itself.

• Automated Backup and Snapshot Operations

  • Scenario: Scheduled backup jobs using tools like Veeam Backup & Replication or Commvault initiate a “pre-backup freeze.” These agents lock application data files (such as SQL databases or Exchange mailboxes) to ensure consistency before creating snapshots, triggering the YARA rule’s file-locking logic.
  • Filter/Exclusion: Exclude events where the initiating process is identified as vbr.exe (Veeam), commtask.exe, or any process running under the “System” account during defined maintenance windows (e.g., 02:00 – 04:00 UTC).

• Group Policy Object (GPO) Software Deployment

  • Scenario: During a scheduled Group Policy refresh, the Microsoft SCCM (Configuration Manager) or Windows Update for Business service deploys new patches. The deployment agent locks configuration files and registry keys to apply updates without user interference, which can be flagged as an abnormal locking event by DMALocker4.
  • **Filter/