Upackv029betaDwing

Hunt Hypothesis

This YARA rule targets the Upack v0.29 beta Dwing variant, a known Windows packer often used by threat actors to compress and obfuscate malicious payloads to evade static analysis. Proactively hunting for this specific signature in Azure Sentinel allows the SOC to identify potentially compromised endpoints or staging areas where adversaries are preparing to deploy packed executables before they trigger more complex runtime behaviors.

YARA Rule

rule Upackv029betaDwing
{
      meta:
		author="malware-lu"
strings:
		$a0 = { E9 [4] 42 79 44 77 69 6E 67 40 00 00 00 50 45 00 00 4C 01 02 [20] 29 }

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: A developer or DevOps engineer runs a local build script using Python or Node.js that dynamically generates a small utility script (e.g., a .py or .js file) and executes it via python.exe or node.exe. The generated file often contains repetitive string patterns or specific header bytes that match the Upackv029betaDwing YARA signature, especially if the script includes embedded base64 blobs or specific magic numbers used for internal tooling.

  • Filter/Exclusion: Exclude files located in common development directories (e.g., C:\Users\<user>\Projects\, C:\src\, C:\workspace\) or exclude processes where the parent is python.exe, node.exe, or npm.exe and the file extension is .py, .js, or .ts.

• Scenario: An IT administrator uses PowerShell to deploy a small configuration helper script or a custom .ps1 wrapper that downloads and executes a lightweight binary (e.g., a specific version of curl.exe or a custom .exe helper) from an internal repository. If this helper binary is a stripped-down build or contains specific debug symbols, it may trigger the rule.

  • Filter/Exclusion: Exclude files in the C:\ProgramData\ or C:\Temp\ directories if the parent process is powershell.exe or pwsh.exe and the file size is less than 500KB. Additionally, exclude known internal tool binaries by SHA256 hash if they are consistently flagged.

• Scenario: A scheduled task runs a Java application (e.g., a monitoring agent or log collector) that writes temporary JAR files or native libraries to the C:\Windows\Temp\ or `C:\Users<user>\App