WWPACKv305c4ExtractablePasswordchecking

Hunt Hypothesis

This hypothesis targets the presence of the WWPACKv305c4 packer, which is frequently used to obfuscate malicious payloads and protect extractable passwords from static analysis. Proactively hunting for this signature in Azure Sentinel allows the SOC team to identify potentially hidden or obfuscated executables before they can be deployed to compromise workloads or data.

YARA Rule

rule WWPACKv305c4ExtractablePasswordchecking
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 03 05 80 1A B8 [2] 8C CA 03 D0 8C C9 81 C1 [2] 51 B9 [2] 51 06 06 B1 ?? 51 8C D3 }

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 that uses 7z (7-Zip) or unrar to extract a proprietary .rar or .7z archive containing source code or configuration files. The YARA rule may match the specific password-checking logic embedded in the extraction utility or the temporary files created during the unpacking process.

  • Filter/Exclusion: Exclude processes where the parent process is 7z.exe, 7zG.exe, unrar.exe, or tar.exe and the file path contains \temp\, \build\, or \workspace\. Additionally, exclude if the command line arguments contain -p (password) or --password.

• Scenario: An IT administrator uses a GUI-based archive manager like WinRAR or PeaZip to manually extract a large software distribution package (e.g., a new version of a commercial IDE or database client) onto a shared network drive. The extraction process spawns child processes that handle password verification, triggering the detection.

  • Filter/Exclusion: Exclude if the parent process is WinRAR.exe, WinRAR.exe (64-bit), or PeaZip.exe and the target file path resides in standard application directories such as C:\Program Files\, C:\Program Files (x86)\, or D:\Software\.

• Scenario: A scheduled maintenance job (e.g., a PowerShell script or batch file) runs nightly to unpack encrypted log archives or backup sets for analysis. The script invokes a command-line tool like bsdtar or python -m zipfile to extract files, and the password-checking routine within the library triggers the YARA match.

  • Filter/Exclusion: Exclude if the parent process is powershell.exe, pwsh.exe, or `cmd.exe