Unsanitized URL schemes in MDEx Quill Delta output allow javascript: injection (XSS)

Summary

Improper Neutralization of Input During Web Page Generation (XSS) vulnerability in leandrocp mdex allows cross-site scripting via unsanitized URL schemes in Quill Delta output. 'Elixir.MDEx':to_delta/2 converts Markdown into a Quill Delta. 'Elixir.MDEx.DeltaConverter':default_convert_node/3 in lib/mdex/delta_converter.ex copies the URL of a link, wikilink, or image node directly from the parsed Markdown into the Delta "link" or "image" attribute without applying a scheme allowlist or any normalization. An attacker who controls the Markdown text can supply a javascript: URL (for example click) that survives verbatim into the Delta attribute. When the Delta is rendered to HTML by a downstream renderer (such as quill-delta-to-html or the Quill client), the attribute becomes an <a href> or <img src>, and the javascript: scheme executes in the browser of anyone who views the rendered content. The link and wikilink cases are the strongest vectors because javascript: in an href executes on click; the image case is lower impact because javascript: in <img src> generally does not execute in modern browsers. This issue affects mdex: from 0.8.3 before 0.13.2.

Timeline

1. Jun 29, 2026, 7:10 PM UTCCVE published
2. Jun 29, 2026, 8:48 PM UTCCISA SSVC assessment

   Exploitation: poc · Automatable: no · Technical impact: partial

3. Jun 30, 2026, 4:38 AM UTCRecord last updated

Affected versions

• mdex

  From 0.8.3 · fixed in 0.13.2

• leandrocp/mdex

  Version range not reported

References 4