EncryptPEV220070411WFS

Hunt Hypothesis

This detection identifies potential fileless or packed malware activity where adversaries utilize encryption to obfuscate executable code and evade signature-based defenses. Proactive hunting for this behavior in Azure Sentinel is essential to uncover early-stage threats that may bypass traditional antivirus solutions by leveraging encrypted process execution patterns before they escalate into full-scale incidents.

YARA Rule

rule EncryptPEV220070411WFS
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 60 9C 64 FF 35 00 00 00 00 E8 1B 02 00 00 00 00 00 00 00 00 00 00 00 00 00 00 [8] 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 [36] 00 00 00 00 6B 65 72 6E 65 6C 33 32 2E 64 6C 6C 00 00 00 47 65 74 54 65 6D 70 50 61 74 68 41 00 00 00 43 72 65 61 74 65 46 69 6C 65 41 00 00 00 43 72 65 61 74 65 46 69 6C 65 4D 61 70 70 69 6E 67 41 00 00 00 4D 61 70 56 69 65 77 4F 66 46 69 6C 65 00 00 00 55 6E 6D 61 70 56 69 65 77 4F 66 46 69 6C 65 00 00 00 43 6C 6F 73 65 48 61 6E 64 6C 65 00 00 00 4C 6F 61 64 4C 69 62 72 61 72 79 41 00 00 00 47 65 74 50 72 6F 63 41 64 64 72 65 73 73 00 00 00 45 78 69 74 50 72 6F 63 65 73 73 }

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 5 specific false positive scenarios for the EncryptPEV220070411WFS detection rule, along with suggested filters and exclusions tailored for a legitimate enterprise environment:

• Antivirus Engine Real-Time Scanning of Encrypted Archives

  • Scenario: The real-time protection engine of Microsoft Defender Antivirus (MSE) or Symantec Endpoint Protection scans large .zip or .7z files containing encrypted payloads. The YARA rule triggers because the scanning process temporarily writes these encrypted structures to memory or disk, mimicking the behavior of a malicious encryptor.
  • Filter/Exclusion: Create an exclusion for the specific file paths where temporary scan caches are stored (e.g., C:\ProgramData\Microsoft\Windows Defender\Support on Windows) and exclude the process names MsMpEng.exe or Rtvscan64.exe from triggering this rule when accessing .zip, .7z, or .cab extensions.

• Scheduled Backup Jobs Utilizing Encrypted Containers

  • Scenario: A nightly scheduled task runs Veeam Agent for Microsoft Windows or Acronis Cyber Protect, which creates encrypted backup containers (.vbk or .tib files). The rule detects the creation and writing of these large, encrypted binary structures as a potential “fileless” encryption event.
  • Filter/Exclusion: Exclude the specific service accounts used for backups (e.g., DOMAIN\BackupSvc) and filter out events where the parent process is VeeamAgent.exe or AcronisCyberProtectService.exe. Additionally, exclude file extensions .vbk, .tib, and .bak from the detection scope during business hours (08:00–18:00).

• **Software Deployment via SCCM/Intune