PEPROTECT09

Hunt Hypothesis

This detection identifies potential malicious Portable Executable (PE) files that match specific YARA signatures, indicating adversaries attempting to introduce custom or obfuscated binaries into the environment. Proactive hunting for this behavior in Azure Sentinel is essential to uncover low-severity threats that may evade standard signature-based defenses and serve as early indicators of a broader compromise chain.

YARA Rule

rule PEPROTECT09
{
      meta:
		author="malware-lu"
strings:
		$a0 = { E9 CF 00 00 00 0D 0A 0D 0A C4 C4 C4 C4 C4 C4 C4 C4 C4 C4 C4 }

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 PEPROTECT09 detection rule, including suggested filters and exclusions tailored for an enterprise environment:

• Scenario: Automated Patch Deployment via SCCM/Intune

  • Context: System Center Configuration Manager (SCCM) or Microsoft Intune agents execute ccmsetup.exe or IntuneManagementExtension.exe to install cumulative updates. These processes often spawn temporary child processes that load custom PE modules, triggering the rule’s signature for “unusual PE structure” during the installation phase.
  • Filter/Exclusion: Create a process exclusion based on the parent image path: C:\Windows\CCM\* and C:\Program Files (x86)\Microsoft Intune Management Extension\*. Additionally, exclude events where the process command line contains keywords like /install, /update, or /deploy.

• Scenario: Scheduled Antivirus Definition Updates

  • Context: Enterprise Endpoint Protection suites (e.g., Microsoft Defender for Endpoint, Symantec Endpoint Protection) run scheduled jobs at 03:00 AM to download and install new definition databases. The update engine often creates a temporary PE file in the %TEMP% directory before merging it into the main database, which mimics the behavior of a suspicious executable injection.
  • Filter/Exclusion: Implement a time-based filter to suppress alerts between 02:30 and 04:30 for processes named MpCmdRun.exe, Symantec Antivirus Console.exe, or DefenderUpdate.exe. Alternatively, exclude the specific directory path C:\ProgramData\Microsoft\Windows Defender\* from the YARA scan scope.

• Scenario: Database Backup and Maintenance Jobs

  • Context: SQL Server Agent jobs running nightly backups often utilize tools like `sqlbackup.exe