AHTeamEPProtector03fakeStonesPEEncryptor20FEUERRADER

Hunt Hypothesis

This detection identifies potential fileless or packed malware activity characterized by specific PE encryptor signatures that may indicate an adversary attempting to obfuscate malicious executables within the endpoint environment. Proactively hunting for this behavior in Azure Sentinel is essential to uncover stealthy threats that evade traditional signature-based defenses, allowing the SOC team to validate false positives and investigate early-stage encryption anomalies before they escalate into broader incidents.

YARA Rule

rule AHTeamEPProtector03fakeStonesPEEncryptor20FEUERRADER
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 90 [46] 90 FF E0 53 51 52 56 57 55 E8 00 00 00 00 5D 81 ED 42 30 40 00 FF 95 32 35 40 00 B8 37 30 40 00 03 C5 2B 85 1B 34 40 00 89 85 27 34 40 00 83 }

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

False Positive Scenarios for AHTeamEPProtector03fakeStonesPEEncryptor20FEUERRADER

• Scenario: Microsoft Defender Antivirus Real-Time Protection Scan

  • Context: The YARA rule detects the PE header structure of encrypted executables. When Microsoft Defender Antivirus performs real-time scanning on a large batch of recently downloaded installer packages (e.g., .msi or .exe from the AppVeyor pipeline), its internal encryption engine may match the “PE Encryptor” signature, triggering an alert even though the files are benign and signed by Microsoft.
  • Suggested Filter/Exclusion: Create a process exclusion in the EDR console for MsMpEng.exe (Microsoft Defender) to ignore alerts generated when the parent process is the Antivirus service scanning files within the C:\ProgramData\Microsoft\Windows Defender\Scans\History\Detection directory.

• Scenario: Automated Backup Encryption via Veeam Agent

  • Context: The enterprise runs a scheduled nightly job using Veeam Agent for Windows. During the backup process, Veeam encrypts temporary staging files before archiving them to the repository. This encryption activity modifies PE headers in a way that mimics the “fake Stones” signature logic of the rule, causing false positives during the 2:00 AM maintenance window.
  • Suggested Filter/Exclusion: Implement a time-based exclusion or a process-specific filter for Veeam.Backup.Service.exe. Configure the detection to suppress alerts originating from this process when the file path contains \Veeam\Backup\Staging and the execution occurs between 01:30 and 04:30 local server time.

• Scenario: Office 365 Click-to-Run Updates

  • Context: