Impact

The Trix editor, in versions prior to 2.1.18, is vulnerable to XSS when a crafted application/x-trix-document JSON payload is dropped into the editor in environments using the fallback Level0InputController (e.g., embedded WebViews lacking Input Events Level 2 support).

The StringPiece.fromJSON method trusted href attributes from the JSON payload without sanitization. An attacker could craft a draggable element containing a javascript: URI in the href attribute that, when dropped into a vulnerable editor, would bypass DOMPurify sanitization and inject executable JavaScript into the DOM.

Exploitation requires a specific environment (Level0InputController fallback) and social engineering (victim must drag and drop attacker-controlled content into the editor). Applications using server-side HTML sanitization (such as Rails' built-in sanitizer) are additionally protected, as the payload is neutralized on save.

Patches

Update Recommendation: Users should upgrade to Trix editor version 2.1.18 or later.

References

The XSS vulnerability was responsibly reported by Hackerone researcher newbiefromcoma.