VxKuku886

Hunt Hypothesis

This rule identifies potential VxKuku886 malware artifacts, a low-severity threat often associated with initial access or fileless execution techniques that may evade standard signature-based detections. Proactively hunting for this indicator in Azure Sentinel allows the SOC to uncover stealthy footholds or dormant payloads that could be leveraged for lateral movement or privilege escalation before they mature into higher-impact compromises.

YARA Rule

rule VxKuku886
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 06 1E 50 8C C8 8E D8 BA 70 03 B8 24 25 CD 21 [5] 90 B4 2F CD 21 53 }

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 uses Visual Studio Code or JetBrains IntelliJ to edit a large source code file (e.g., main.cpp or app.js) that contains specific string literals or hex patterns matching the YARA signature. The editor’s autosave feature writes the file to disk, triggering the detection on the .cpp or .js file.
  • Filter/Exclusion: Exclude files with extensions .cpp, .c, .h, .js, .ts, .py, or .java if the process path contains \Code\ or \IntelliJ\ and the file size is greater than 10KB.
• Scenario: An IT administrator runs 7-Zip or WinRAR to extract a large archive containing a mix of text documents and binary assets. The extraction process creates temporary files in %TEMP% or the target directory that contain embedded metadata or specific byte sequences matching the rule, particularly if the archive includes PDFs or images with specific headers.
  • Filter/Exclusion: Exclude files located in %TEMP%, %LOCALAPPDATA%\Temp, or directories named 7z, rar, or extracted if the parent process is 7z.exe, WinRAR.exe, or tar.exe.
• Scenario: A data analyst uses Python with the pandas library to read a large CSV or Parquet file into memory and then writes it back out as a new file. The binary structure of the Parquet file or specific string patterns in the CSV (e.g., UUIDs, hashes, or specific delimiter sequences) may match the YARA rule’s string conditions.
  • Filter/Exclusion: Exclude files with extensions .parquet, .csv, .json, or .xml if the parent process is python.exe,