AIKIDO-2026-504745

TL;DR

mdex is vulnerable to cross-site scripting when converting Markdown to Quill Delta. MDEx.to_delta/2 passes link, wikilink, and image URLs straight from parsed Markdown into Delta link/image attributes with no scheme allowlist or normalization. An attacker who controls the Markdown can embed javascript: URLs (e.g. [click](javascript:alert(document.cookie))), which survive into the Delta and become a href> or img src> when a downstream renderer (quill-delta-to-html or the Quill client) turns it into HTML. Links and wikilinks are the main risk because javascript: in href runs on click; image URLs are lower impact since modern browsers usually block javascript: in img src>.