Mew10execoder10NorthfoxHCC

Hunt Hypothesis

This rule identifies the presence of the Mew10execoder10NorthfoxHCC YARA signature, which likely indicates a specific malware implant or obfuscated payload associated with the Northfox HCC campaign. Proactively hunting for this signature allows the SOC team to detect low-severity footholds or dormant implants before they are leveraged for lateral movement or data exfiltration within the Azure environment.

YARA Rule

rule Mew10execoder10NorthfoxHCC
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 33 C0 E9 [2] FF FF 6A [5] 70 }

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 Git for Windows or Visual Studio Code to clone a repository or execute a build script that includes a custom, obfuscated JavaScript or Python helper script (e.g., build_helper.js or setup.py) located in a user profile directory (C:\Users\<user>\AppData\Local\... or C:\Users\<user>\Documents\...). The script contains specific string patterns or byte sequences that match the Mew10execoder10NorthfoxHCC signature due to encoding artifacts or common library imports.

  • Filter/Exclusion: Exclude processes where the parent process is code.exe (VS Code), git.exe, or node.exe AND the file path contains \AppData\Local\ or \Documents\ AND the file extension is .js, .py, or .ts.

• Scenario: An IT administrator runs a one-off PowerShell script via PowerShell ISE or pwsh.exe to clean up temporary files or configure network settings. The script is saved in a non-standard location like C:\Temp\ or C:\Users\<admin>\Desktop\ and uses base64-encoded commands or specific string literals (e.g., “Northfox”, “HCC”, or “execoder”) that are part of internal tooling naming conventions or variable names, triggering the YARA rule’s string matches.

  • Filter/Exclusion: Exclude if the parent process is powershell.exe or pwsh.exe AND the script path is under C:\Temp\, C:\Users\<admin>\Desktop\, or C:\Users\<admin>\Downloads\ AND the script name contains keywords like cleanup, config, or setup.

• Scenario: A security engineer or tester uses **Fiddler