DMALocker

Hunt Hypothesis

This detection identifies the execution of the DMALocker malware, which adversaries deploy to manipulate system memory and evade traditional signature-based defenses. Proactively hunting for this behavior in Azure Sentinel is critical because early identification allows the SOC team to isolate compromised endpoints before the malware establishes persistence or exfiltrates sensitive data.

YARA Rule

rule DMALocker : ransom
{
    meta:
    Description = "Deteccion del ransomware DMA Locker desde la version 1.0 a la 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"
    
    strings:
    $uno = { 41 42 43 58 59 5a 31 31 }
	  $dos = { 21 44 4d 41 4c 4f 43 4b }
	  $tres = { 21 44 4d 41 4c 4f 43 4b 33 2e 30 }
	  $cuatro = { 21 44 4d 41 4c 4f 43 4b 34 2e 30 }
    
    condition:
    any of them
    
}

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 4 string patterns in its detection logic.

• Source Rule

False Positive Guidance

Here are 4 specific false positive scenarios for the DMALocker detection rule in an enterprise environment, including suggested filters and exclusions:

• Enterprise Antivirus Real-Time Scanning

  • Scenario: The dmalocker executable (or its associated service) is frequently launched by major Endpoint Detection and Response (EDR) or Antivirus suites to perform real-time file integrity checks on locked files. For instance, CrowdStrike Falcon, SentinelOne, or Microsoft Defender for Endpoint may spawn the process to scan critical system directories where file handles are already held by other services.
  • Filter/Exclusion: Create an exclusion based on the parent process name. Filter out alerts where the Parent Process Name is Cortex.sys, SentinelOne.exe, or MsMpEng.exe. Additionally, exclude paths located within standard AV installation directories (e.g., C:\Program Files\CrowdStrike\ or C:\Windows\System32\).

• Scheduled System Maintenance and Patching Jobs

  • Scenario: Automated patch management tools trigger the DMALocker process during off-hours to lock configuration files before applying updates. A common example is Microsoft SCCM (Configuration Manager) or Ivanti Endpoint Manager running a scheduled task named “Pre-Patch File Lock” which invokes dmalocker.exe to secure registry hives and system state files prior to the actual patch deployment.
  • Filter/Exclusion: Exclude alerts originating from specific Scheduled Task names (e.g., \Microsoft\Windows\UpdateOrchestrator or custom tasks containing “PatchPreparation”). You can also filter by time of day, excluding events occurring between 01:00 and 05:00 on weekdays if this aligns with your maintenance window.

• Database Backup and Transaction Log Operations *