EncryptPEV22006115WFS

Hunt Hypothesis

This detection identifies potential fileless or memory-based encryption activities that may indicate early-stage ransomware execution or data exfiltration attempts within the environment. A proactive hunt is essential to validate these low-severity signals against known benign processes, ensuring that subtle indicators of compromise are not overlooked before they escalate into critical incidents.

YARA Rule

rule EncryptPEV22006115WFS
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 45 50 45 3A 20 45 6E 63 72 79 70 74 50 45 20 56 32 2E 32 30 30 36 2E 31 2E 31 35 }

condition:
		$a0
}

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 EncryptPEV22006115WFS detection rule, including suggested filters and exclusions:

• Scenario: Microsoft Defender Antivirus Real-Time Scanning

  • Context: The YARA rule may flag the MsMpEng.exe process when it scans or updates its definition database, as this executable often utilizes internal encryption routines that match the signature pattern. This is a high-frequency event occurring on every endpoint during scheduled update windows (e.g., 03:00 AM).
  • Suggested Filter: Exclude alerts where the Process Name equals MsMpEng.exe AND the Parent Process Name is smss.exe or svchost.exe.

• Scenario: Veeam Backup & Replication Agent Activity

  • Context: The Veeam Transport Service (VeeamTransportService.exe) frequently encrypts backup chunks and metadata before writing them to the repository. This encryption activity often triggers the rule during nightly backup windows, generating a high volume of alerts for standard data protection workflows.
  • Suggested Filter: Create an exclusion based on Process Name = VeeamTransportService.exe (or VeeamAgent.exe) and restrict the alert to only trigger if the file extension is NOT .vbk, .vbm, or .v2v.

• Scenario: Scheduled Group Policy Script Execution

  • Context: Enterprise environments often deploy PowerShell scripts via Group Policy to encrypt sensitive configuration files (e.g., config.xml or JSON manifests) at logon. The script runner (powershell.exe) invoking an encryption module can trigger this rule repeatedly for every user login event across the domain.
  • Suggested Filter: Exclude alerts where the Command Line contains keywords such as “Group