UPXShit006

Hunt Hypothesis

This detection identifies potential file obfuscation attempts where adversaries utilize the UPX executable packer to conceal malicious payloads within legitimate applications. Proactive hunting for this behavior in Azure Sentinel is essential because UPX packing frequently masks advanced threats from static analysis tools, allowing attackers to bypass initial security controls and execute stealthy operations.

YARA Rule

rule UPXShit006
{
      meta:
		author="malware-lu"
strings:
		$a0 = { B8 [2] 43 00 B9 15 00 00 00 80 34 08 ?? E2 FA E9 D6 FF 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 UPXShit006 detection rule, which targets executables packed with UPX (a popular executable packer often used by both legitimate software and malware):

• Scenario: Automated Patch Deployment via SCCM/Intune

  • Context: Enterprise Configuration Management tools like Microsoft Endpoint Configuration Manager (SCCM) or Intune frequently distribute updates for internal line-of-business applications. These installers are often compressed using UPX to reduce bandwidth usage during deployment across the network. When the endpoint agent scans these newly deployed .exe files, it triggers the rule.
  • Suggested Filter: Create an exclusion based on the process name and file path. Exclude any file where ProcessName is ccmsetup.exe, MicrosoftEdgeUpdate.exe, or IntuneAgent.exe AND the file resides in the C:\Program Files\ or C:\Windows\SoftwareDistribution\Download\ directories.

• Scenario: Scheduled Backup and Archiving Jobs

  • Context: Legacy backup solutions (e.g., Veeam Agent, Acronis Cyber Protect) often utilize UPX-packed helper utilities to compress data before transmission. These jobs run on a strict schedule (e.g., every night at 2:00 AM), generating new packed executables or temporary agents that the YARA rule flags as suspicious due to their high entropy and packing signature.
  • Suggested Filter: Implement a time-based exclusion combined with a file hash allowlist. Exclude alerts generated between 01:00 and 05:00 local time for files matching known SHA-256 hashes of the backup vendor’s core engine (e.g., Veeam.Backup.Service.exe).

• Scenario: Deployment of Third-Party Security Agents

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