DCryptPrivate09bdrmist

Hunt Hypothesis

This hunt hypothesis targets potential malware or suspicious artifacts identified by the DCryptPrivate09bdrmist YARA signature to uncover early-stage encryption-related threats within the environment. Proactively hunting for this indicator in Azure Sentinel allows the SOC team to validate low-severity detections before they escalate into ransomware incidents, ensuring comprehensive coverage of private decryption activities that may otherwise be overlooked.

YARA Rule

rule DCryptPrivate09bdrmist
{
      meta:
		author="malware-lu"
strings:
		$a0 = { B9 [3] 00 E8 00 00 00 00 58 68 [3] 00 83 E8 0B 0F 18 00 D0 00 48 E2 FB C3 }

condition:
		$a0 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

Here are 4 specific false positive scenarios for the DCryptPrivate09bdrmist detection rule, including suggested filters and exclusions:

• Scenario: Scheduled Backup Encryption by Veeam Agent

  • Context: The nightly scheduled job of the Veeam Agent for Microsoft Windows executes a full backup. During this process, the agent invokes the native BitLocker or proprietary encryption engine to encrypt the backup metadata and data streams on the disk before transmission. This triggers the YARA rule due to the high volume of encrypted I/O operations matching the “DCrypt” signature pattern.
  • Suggested Filter/Exclusion: Create a process exclusion for veeamagent.exe (Veeam Agent) and its child processes, specifically limiting the scope to the backup window hours (e.g., 02:00 – 04:00 UTC). Alternatively, add a filter excluding events where the parent process is vssvc.exe (Volume Shadow Copy Service) during scheduled maintenance windows.

• Scenario: Microsoft Defender Antivirus Real-Time Scanning

  • Context: The Microsoft Defender Antivirus service (MsMpEng.exe) performs real-time scanning on large, encrypted database files (e.g., .enc or .dbf extensions) located in the C:\ProgramData\CorporateApps directory. As Defender reads and decrypts these files for signature matching, it generates memory patterns that mimic the behavior of a malicious encryption routine detected by the rule.
  • Suggested Filter/Exclusion: Configure an exclusion path in Microsoft Defender Security Center for the specific directory C:\ProgramData\CorporateApps. Additionally, add a process exclusion for MsMpEng.exe when the file extension is .enc or .dbf, ensuring that routine scanning does not trigger alerts.

• **Scenario: Azure Active Directory Connect Sync Service