PEProtectv09

Hunt Hypothesis

This detection identifies potentially malicious Portable Executable (PE) files that match specific structural anomalies or embedded signatures defined by the PEProtectv09 YARA rule, signaling possible file-based threats such as trojans or custom malware. Proactively hunting for these indicators in Azure Sentinel allows the SOC team to uncover stealthy adversary behaviors that may evade standard signature-based defenses, ensuring early identification of compromised assets before they escalate into critical incidents.

YARA Rule

rule PEProtectv09
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 52 51 55 57 64 67 A1 30 00 85 C0 78 0D E8 [4] 58 83 C0 07 C6 ?? C3 }
	$a1 = { E9 ?? 00 00 00 0D 0A 0D 0A C4 C4 C4 C4 C4 C4 C4 C4 C4 C4 C4 C4 C4 C4 C4 C4 C4 C4 C4 C4 C4 C4 C4 C4 C4 C4 C4 C4 C4 C4 C4 C4 C4 C4 C4 C4 C4 C4 C4 C4 C4 C4 C4 C4 C4 C4 C4 C4 C4 C4 C4 C4 C4 C4 C4 0D 0A 50 45 2D 50 52 4F 54 45 43 54 20 30 2E 39 20 28 43 29 6F }

condition:
		$a0 at pe.entry_point or $a1
}

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 2 string patterns in its detection logic.

• Source Rule

False Positive Guidance

Here are 3-5 specific false positive scenarios for the PEProtectv09 detection rule, including suggested filters and exclusions tailored for an enterprise environment:

• Scenario: Scheduled Antivirus Signature Updates via Windows Update Service

  • Context: The wuauserv (Windows Update) service or third-party agents like CrowdStrike Falcon or Carbon Black frequently download and execute new definition files (.cab or .dll) that match the PEProtect signature patterns. These legitimate updates often trigger the rule due to their embedded cryptographic signatures and specific PE header structures.
  • Suggested Filter/Exclusion: Create a process exclusion for wuauserv.exe and falcon.sys (or the specific agent executable of your EDR) when running under the context of the SYSTEM account. Additionally, filter out alerts where the file path contains \Windows\SoftwareDistribution\Download\ or \ProgramData\CrowdStrike\.

• Scenario: Automated Software Deployment via Microsoft Endpoint Configuration Manager (SCCM)

  • Context: During business hours, SCCM (or similar tools like Ivanti or Jamf) pushes application updates to endpoints. The deployment client (ccmexec.exe) extracts and installs new executables that possess the specific PE characteristics monitored by PEPProtectv09. This often occurs during maintenance windows where bulk installations happen simultaneously.
  • Suggested Filter/Exclusion: Exclude alerts generated by ccmexec.exe or smsengine.exe running under the Local System account. Implement a time-based suppression rule to ignore detections from these processes between 02:00 and 06:00 UTC, aligning with standard maintenance windows.

• Scenario: Legitimate Script Execution by PowerShell for Administrative Tasks

  • Context: Administrators frequently run