Upackv029Betav031BetaDwing

Hunt Hypothesis

This hypothesis targets the presence of the Upack v0.29 Beta packer, a tool frequently used by adversaries to obfuscate malicious payloads and evade static analysis during initial access or execution phases. Proactively hunting for this specific YARA signature in Azure Sentinel allows the SOC to identify potentially compromised hosts or files before the packed malware can unpack and execute its full payload, reducing the mean time to detection for low-severity but high-impact threats.

YARA Rule

rule Upackv029Betav031BetaDwing
{
      meta:
		author="malware-lu"
strings:
		$a0 = { BE 88 01 [2] AD 8B F8 95 AD 91 F3 A5 AD B5 ?? F3 }

condition:
		$a0
}

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 build engineer manually extracts a legacy .zip or .tar.gz archive containing custom C/C++ source code or pre-compiled object files in a temporary directory (e.g., C:\Temp\build_artifacts) using a standard tool like 7-Zip or WinRAR. The YARA rule may match specific byte patterns in the uncompressed binary or object files that resemble the “Upack” signature, especially if the archive contains mixed content or specific header structures.

  • Filter/Exclusion: Exclude files located in common temporary or build directories (e.g., C:\Temp\, C:\Builds\, C:\Users\<user>\AppData\Local\Temp\) and limit the scan to files with extensions like .exe, .dll, or .sys rather than all file types. Additionally, exclude processes known to be extraction tools (e.g., 7z.exe, WinRAR.exe) from triggering the alert if the file is newly created by them.

• Scenario: An IT administrator installs or updates a third-party application that includes a self-extracting installer (e.g., NSIS-based installers or Inno Setup packages). During installation, the installer unpacks a compressed payload (often a .cab or custom compressed format) into a temporary folder. The YARA rule may detect the unpacked intermediate files or the installer binary itself if it contains embedded compressed data that matches the “Upackv029” pattern.

  • Filter/Exclusion: Exclude files created by known installer processes (e.g., setup.exe, installer.exe, nsis.exe) and files located in standard installation temporary paths (e.g., C:\Windows\Installer\, C:\ProgramData\Package Cache\). Consider whitelisting specific installer executables or their associated temporary directories.