XCF File Format by Adeline Software additional

Hunt Hypothesis

This hypothesis targets the presence of XCF files, a proprietary format used by Adeline Software, which may indicate specific application usage or potential data staging by adversaries leveraging niche tools for file manipulation. Proactively hunting for these files in Azure Sentinel helps identify unusual file artifacts that could signal targeted activity or the use of specialized software for obfuscation or data exfiltration within the environment.

YARA Rule

rule XCF_File_Format_by_Adeline_Software_additional: PEiD
{
    strings:
        $a = { 46 72 61 6D 65 4C 65 6E F4 0F }
    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 marketing or design team uses Adobe Photoshop to save native project files for ongoing editing, resulting in the creation of .xcf files on user workstations or shared network drives.
  • Filter/Exclusion: Exclude files located in known user profile directories (e.g., C:\Users\*\Documents\, C:\Users\*\Pictures\) or specific shared folders designated for creative assets (e.g., \\fileserver\marketing\projects\).
• Scenario: An IT administrator performs a system backup or image capture using Acronis True Image or Veeam Agent, which may create temporary .xcf-named container files or intermediate archives during the backup process on the local disk.
  • Filter/Exclusion: Exclude files created by known backup service accounts (e.g., svc_backup, admin_backup) or located in standard backup staging directories (e.g., C:\ProgramData\Acronis\, C:\VeeamBackup\).
• Scenario: A software development team uses GIMP (GNU Image Manipulation Program) as a lightweight alternative to Photoshop for UI/UX asset creation, saving .xcf files in project repositories synced via OneDrive for Business or SharePoint.
  • Filter/Exclusion: Exclude files within synchronized cloud folders (e.g., C:\Users\*\OneDrive - [Company]\Projects\) or specific development workspace paths (e.g., C:\dev\ui-assets\).
• Scenario: A CI/CD pipeline step in Jenkins or Azure DevOps runs a build job that processes image assets, temporarily creating .xcf files in the build workspace directory before conversion to PNG/JPG.
  • Filter/Exclusion: Exclude files located in standard CI/CD workspace directories (e