recent Emotet packer pdb string

Hunt Hypothesis

This detection identifies potential Emotet malware infections by analyzing executable files for specific PDB strings indicative of its unique packing mechanism. Proactively hunting for this signature in Azure Sentinel is critical to establish early visibility into initial infection vectors before adversaries can execute their full payload and propagate laterally across the network.

YARA Rule

rule emotet_packer {
   meta:
      description = "recent Emotet packer pdb string"
      author = "Marc Salinas (@Bondey_m)"
      reference = "330fb2954c1457149988cda98ca8401fbc076802ff44bb30894494b1c5531119"
	  reference = "d08a4dc159b17bde8887fa548b7d265108f5f117532d221adf7591fbad29b457"
	  reference = "7b5b8aaef86b1a7a8e7f28f0bda0bb7742a8523603452cf38170e5253f7a5c82"
	  reference = "e6abb24c70a205ab471028aee22c1f32690c02993b77ee0e77504eb360860776"
	  reference = "5684850a7849ab475227da91ada8ac5741e36f98780d9e3b01ae3085a8ef02fc"
	  reference = "acefdb67d5c0876412e4d079b38da1a5e67a7fcd936576c99cc712391d3a5ff5"
	  reference = "14230ba12360a172f9f242ac98121ca76e7c4450bfcb499c2af89aa3a1ef7440"
	  reference = "4fe9b38d2c32d0ee19d7be3c1a931b9448904aa72e888f40f43196e0b2207039"
	  reference = "e31028282c38cb13dd4ede7e9c8aa62d45ddae5ebaa0fe3afb3256601dbf5de7"
      date = "2017-12-12"
    strings:
		$pdb1 = "123EErrrtools.pdb"
		$pdb2=  "gGEW\\F???/.pdb"

    condition:
       $pdb1 or $pdb2
}

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.

References

• e31028282c38cb13dd4ede7e9c8aa62d45ddae5ebaa0fe3afb3256601dbf5de7
• Source Rule

False Positive Guidance

Here are 4 specific false positive scenarios for the “recent Emotet packer pdb string” detection rule, along with suggested filters or exclusions:

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

  • Context: During nightly maintenance windows, SCCM pushes updates to the C:\Windows\System32 directory. The deployment process often involves unpacking compressed binaries and generating temporary PDB files that match the Emotet packer signature before the final installation is committed.
  • Filter/Exclusion: Exclude alerts where the parent process is ccmsetup.exe or WUAHandler.exe running under the SYSTEM account, specifically when the file path contains \Microsoft\CCM\ or \Windows\SoftwareDistribution\.

• Scenario: Antivirus Engine Scanning and Quarantine Operations

  • Context: Enterprise AV solutions like CrowdStrike Falcon or Microsoft Defender for Endpoint frequently extract and analyze packed executables in their quarantine folders. When the engine unpacks a file to scan its internal structure, it may generate PDB artifacts that mimic Emotet’s packing behavior.
  • Filter/Exclusion: Create an exclusion rule based on process names C:\Program Files\CrowdStrike\FalconSensor\csfalcon.exe or C:\Windows\System32\Microsoft Defender Antivirus\MsMpEng.exe, ensuring the file path is within the vendor’s specific quarantine directory (e.g., \Quarantine\).

• Scenario: Scheduled Backup and Archiving Jobs using Veeam or Acronis

  • Context: Scheduled backup jobs often compress large datasets into temporary archives. The archiving software utilizes packing algorithms that generate PDB strings similar to Emotet’s signature during the compression phase, particularly when processing .msi or .exe payloads within the archive stream.