PEArmor046Hying

Hunt Hypothesis

This detection identifies potential malicious Portable Executable (PE) files exhibiting specific structural anomalies or embedded signatures defined by the PEArmor046Hying YARA rule, which may indicate early-stage malware or obfuscated payloads. Proactively hunting for these indicators in Azure Sentinel allows the SOC team to uncover stealthy threats that might evade traditional signature-based defenses before they escalate into active incidents.

YARA Rule

rule PEArmor046Hying
{
      meta:
		author="malware-lu"
strings:
		$a0 = { E8 AA 00 00 00 2D [2] 00 00 00 00 00 00 00 00 00 3D [2] 00 2D [2] 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 4B [2] 00 5C [2] 00 6F [2] 00 00 00 00 00 4B 45 52 4E 45 4C 33 32 2E 64 6C 6C 00 00 00 00 47 65 74 50 72 6F 63 41 64 64 72 65 73 73 00 00 00 47 65 74 4D 6F 64 75 6C 65 48 61 6E 64 6C 65 41 00 00 00 4C 6F 61 64 4C 69 62 72 61 72 79 41 }
	$a1 = { E8 AA 00 00 00 2D [3] 00 00 00 00 00 00 00 00 3D }

condition:
		$a0 at pe.entry_point or $a1 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 2 string patterns in its detection logic.

• Source Rule

False Positive Guidance

Here are 5 specific false positive scenarios for the PEArmor046Hying detection rule, along with targeted filtering strategies:

• Scenario: Microsoft Office Click-to-Run Updates

  • Context: The OfficeClickToRun.exe process periodically launches background tasks to download and install feature updates or hotfixes. These processes often spawn child processes that load custom PE (Portable Executable) modules with specific header structures matching the YARA signature, triggering alerts during routine maintenance windows.
  • Filter/Exclusion: Exclude file paths containing C:\Program Files\Microsoft Office\root\Office16 and process names matching OfficeClickToRun.exe. Additionally, add a time-based filter to suppress alerts between 02:00 and 04:00 UTC when updates typically run.

• Scenario: Antivirus Real-Time Scanning (CrowdStrike/Falcon)

  • Context: Endpoint Detection and Response (EDR) agents like CrowdStrike Falcon or Microsoft Defender perform deep heuristic scanning of newly downloaded executables. When the agent scans a legitimate installer or script, it may generate memory dumps or temporary PE files that mimic the signature logic defined in PEArmor046Hying.
  • Filter/Exclusion: Create an exclusion for process trees where the parent process is C:\Program Files\CrowdStrike\FalconSensor\csfalcon.exe or C:\Windows\System32\Microsoft Defender Antivirus\mpcmdrun.exe. Filter out events where the file extension is .tmp and the file age is less than 5 minutes.

• Scenario: Scheduled PowerShell Deployment Jobs

  • Context: IT Operations teams utilize scheduled tasks (Task Scheduler) to deploy configuration scripts via powershell.exe. These jobs often load compiled .NET assemblies or custom PE modules into memory for execution