FileBrowser Quantum: Stored XSS in public share page via unsanitized share metadata (text/template misuse)

Summary

Stored XSS is possible via share metadata fields (e.g., title, description) that are rendered into HTML for /public/share/<hash> without context-aware escaping. The server uses text/template instead of html/template, allowing injected scripts to execute when victims visit the share URL.

Details

The server renders public/index.html using text/template and injects user-controlled share fields (title/description/etc.) into HTML contexts. text/template does not perform HTML contextual escaping like html/template. Because share metadata is persistent, the payload becomes stored and executes whenever a victim opens the affected share page.

Relevant code paths:

• backend/http/static.go (template rendering and share metadata assignment)
• backend/http/httpRouter.go (template initialization)
• frontend/public/index.html (insertion points for title/description and related fields)

PoC

1. Login as a user with share creation permission.
2. Create a share (POST /api/share) with malicious metadata:
   • title = </title><script>alert("xss")</script><title>
3. Open the resulting /public/share/<hash> URL in a browser.
4. Expected: Payload is safely escaped and displayed as text.
5. Actual: JavaScript executes in victim's browser (stored XSS).

Tested on Docker image: gtstef/filebrowser:stable (version v1.2.1-stable).

Impact

• Arbitrary script execution in application origin.
• Potential account/session compromise, CSRF-like action execution, data exfiltration from authenticated contexts.
• Affects anyone (including unauthenticated visitors) opening the malicious share URL.
• The XSS is stored and persistent — no social engineering beyond sharing the link is required.