Crunch 5 Bit Arts additional

Hunt Hypothesis

This hypothesis targets the presence of the “Crunch 5 Bit Arts” YARA signature, which indicates the execution or persistence of a specific low-severity artifact or script often associated with benign or niche tooling. Proactively hunting for this signature in Azure Sentinel helps distinguish between expected operational noise and potential unauthorized script execution, ensuring that low-fidelity indicators are not overlooked during broader threat investigations.

YARA Rule

rule Crunch_5_Bit_Arts_additional: PEiD
{
    strings:
        $a = { EB 10 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 55 E8 00 00 00 00 5D 81 ED 18 00 00 00 8B C5 55 60 9C 2B 85 E9 06 00 00 89 85 E1 06 00 00 FF 74 24 2C E8 BB 01 00 00 0F 82 92 05 00 00 E8 F1 03 00 00 49 0F 88 86 05 00 00 68 6C D9 B2 96 33 C0 50 E8 24 }
    condition:
        $a 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 QA engineer uses GIMP or Aseprite to create or edit 5-bit palette assets (common in retro-style game development or UI design) and saves the file to a shared network drive or local user profile.
  • Filter/Exclusion: Exclude files with extensions .ase, .aseprite, .xcf, or .png located in designated development directories (e.g., C:\Projects\, D:\Assets\) or owned by service accounts associated with CI/CD pipelines.
• Scenario: An IT administrator runs a scheduled PowerShell or Python script using Pillow (Python Imaging Library) or ImageMagick to batch-process legacy graphics for a digital signage system, explicitly converting images to 5-bit color depth to reduce bandwidth.
  • Filter/Exclusion: Exclude processes where the parent process is python.exe, pwsh.exe, or magick.exe and the command line contains arguments like -colorspace, -depth 5, or convert targeting specific output directories (e.g., C:\Signage\Content\).
• Scenario: A marketing team uses Adobe Photoshop or Affinity Photo to export a logo or banner with a specific 5-bit palette constraint for print or low-bandwidth web delivery, saving the result to a mapped network share.
  • Filter/Exclusion: Exclude files created by photoshop.exe or affinityphoto.exe where the file size is under 5MB and the path includes keywords like Marketing, Assets, or Exports.
• Scenario: A game server or application uses SDL (Simple DirectMedia Layer) or LibGDX to load pre-compressed 5-bit texture assets at startup, creating temporary cache files in the user’s %TEMP% or `%APPDATA