Upackv01xv02xDwing

Hunt Hypothesis

This rule detects the presence of the Upack v0.1 and v0.2 packers, which are commonly used by adversaries to compress and obfuscate malicious executables to evade static analysis. Proactively hunting for these signatures in Azure Sentinel helps identify potentially packed malware artifacts that may be staging or executing on endpoints, allowing the SOC to investigate suspicious processes before they fully deploy their payload.

YARA Rule

rule Upackv01xv02xDwing
{
      meta:
		author="malware-lu"
strings:
		$a0 = { BE 88 01 [2] AD 8B F8 95 }

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

• Scenario: Execution of the Upack utility (a common Windows unpacking tool) by a system administrator or automated script to extract compressed archives (e.g., .zip, .rar, .7z) during software deployment or log collection.
  • Filter/Exclusion: Exclude processes where the parent process is a known deployment tool (e.g., wsadmin.exe, sc.exe, powershell.exe with specific arguments) or where the command line contains standard unpacking flags (e.g., /x, /e, -o). Additionally, exclude if the process path resides in a standard administrative tools directory (e.g., C:\Program Files\7-Zip\, C:\Sysinternals\).
• Scenario: A scheduled maintenance job or service (e.g., Task Scheduler running a custom script) that uses Upack to decompress temporary files or configuration backups before processing, often running under a service account like NT AUTHORITY\SYSTEM or a dedicated svc_backup account.
  • Filter/Exclusion: Exclude if the parent process is svchost.exe (with specific service names like Schedule or WSearch) or if the user context is a known service account (e.g., DOMAIN\svc_backup, NT AUTHORITY\SYSTEM). Also, consider excluding if the working directory is a known temp or backup path (e.g., C:\Temp\, D:\Backups\).
• Scenario: Development or QA teams using Upack as part of a build pipeline or local testing environment where developers manually extract dependency packages or test data sets.
  • Filter/Exclusion: Exclude if the user belongs to a specific AD group (e.g., DevTeam, QA_Access) or if the process is launched from a known development directory (e.g.,