CVE-2026-54889 – Unsanitized URL schemes in MDEx Quill Delta output allow javascript: injection (XSS)

CVE ID :CVE-2026-54889

Published : June 29, 2026, 7:10 p.m. | 35 minutes ago

Description :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](javascript:alert(document.cookie))) 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 or , 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 generally does not execute in modern browsers.

This issue affects mdex: from 0.8.3 before 0.13.2.

Severity: 5.1 | MEDIUM

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