PoPa001PackeronPascalbagie

Hunt Hypothesis

This detection identifies processes exhibiting characteristics of the Pascal Bagie packer, which adversaries often utilize to obfuscate malicious payloads and evade signature-based defenses. Proactively hunting for this behavior in Azure Sentinel allows the SOC team to uncover stealthy execution patterns that may indicate early-stage malware deployment or supply chain compromise before traditional alerts trigger.

YARA Rule

rule PoPa001PackeronPascalbagie
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 55 8B EC 83 C4 EC 53 56 57 33 C0 89 45 EC B8 A4 3E 00 10 E8 30 F6 FF FF 33 C0 55 68 BE 40 00 10 [4] 89 20 6A 00 68 80 00 00 00 6A 03 6A 00 6A 01 68 00 00 00 80 8D 55 EC 33 C0 E8 62 E7 FF FF 8B 45 EC E8 32 F2 FF FF 50 E8 B4 F6 FF FF A3 64 66 00 10 33 D2 55 68 93 40 00 10 64 FF 32 64 89 22 83 3D 64 66 00 10 FF 0F 84 3A 01 00 00 6A 00 6A 00 6A 00 A1 64 66 00 10 50 E8 9B F6 FF FF 83 E8 10 50 A1 64 66 00 10 50 E8 BC F6 FF FF 6A 00 68 80 66 00 10 6A 10 68 68 66 00 10 A1 64 66 00 10 50 E8 8B F6 FF FF }

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 4 specific false positive scenarios for the PoPa001PackeronPascalbagie detection rule, including suggested filters and exclusions:

• Scenario: Microsoft Office Click-to-Run (C2R) Self-Update Mechanism

  • Context: The Microsoft Office C2R update service (OfficeClickToRun.exe) frequently downloads and unpacks new feature packages or hotfixes. During this process, it extracts compressed payloads that match the Pascal-based packing signatures detected by the rule.
  • Filter/Exclusion: Add a path exclusion for C:\Program Files\Microsoft Office\root\Office16\ and exclude processes with the image name OfficeClickToRun.exe. Alternatively, filter out events where the parent process is OfficeClickToRun.exe.

• Scenario: Antivirus Scheduled Malware Definition Updates

  • Context: Enterprise antivirus solutions like CrowdStrike Falcon, SentinelOne, or Symantec Endpoint Protection run scheduled jobs to download and unpack new definition databases. These updates often utilize Pascal-based archive formats for their payload containers, triggering the rule during nightly maintenance windows.
  • Filter/Exclusion: Create a time-based exclusion (e.g., 02:00 – 04:00 local time) combined with a process whitelist for known AV services such as FalconService.exe, SentinelOneAgent.exe, or Symantec Antivirus Service.

• Scenario: Software Deployment via SCCM/Intune Application Installation

  • Context: When IT administrators deploy applications using Microsoft Endpoint Configuration Manager (SCCM) or Intune, the client agent (ccmexec.exe or IntuneManagementExtension) often unpacks installer packages (MSI/EXE) that contain Pascal-compiled components. This is common during