https://github.com/leandrocp/mdex/security/advisories/GHSA-4383-7xfp-gpph

{"timestamp":"2026-06-29T20:48:34.044130Z","id":"CVE-2026-54889","options":[{"exploitation":"poc"},{"automatable":"no"},{"technicalImpact":"partial"}],"role":"CISA Coordinator","version":"2.0.3"}

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 <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.

AV:N/AC:L/AT:N/PR:N/UI:A/VC:L/VI:L/VA:N/SC:L/SI:L/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

CWE-79

https://cna.erlef.org/cves/CVE-2026-54889.html

https://github.com/leandrocp/mdex/commit/2817147f5b87ce7186aa604c9ee72499485b8f2f

https://github.com/leandrocp/mdex/security/advisories/GHSA-4383-7xfp-gpph

https://osv.dev/vulnerability/EEF-CVE-2026-54889

[{"vendor":"leandrocp","product":"mdex","defaultStatus":"unaffected","collectionURL":"https://repo.hex.pm","packageName":"mdex","cpes":["cpe:2.3:a:leandrocp:mdex:*:*:*:*:*:*:*:*"],"modules":["'Elixir.MDEx'","'Elixir.MDEx.DeltaConverter'"],"programFiles":["lib/mdex.ex","lib/mdex/delta_converter.ex"],"programRoutines":[{"name":"'Elixir.MDEx':to_delta/2"},{"name":"'Elixir.MDEx.DeltaConverter':convert/2"},{"name":"'Elixir.MDEx.DeltaConverter':default_convert_node/3"}],"repo":"https://github.com/leandrocp/mdex","packageURL":"pkg:hex/mdex","versions":[{"version":"0.8.3","lessThan":"0.13.2","versionType":"semver","status":"affected"}]},{"vendor":"leandrocp","product":"mdex","defaultStatus":"unaffected","collectionURL":"https://github.com","packageName":"leandrocp/mdex","cpes":["cpe:2.3:a:leandrocp:mdex:*:*:*:*:*:*:*:*"],"modules":["'Elixir.MDEx'","'Elixir.MDEx.DeltaConverter'"],"programFiles":["lib/mdex.ex","lib/mdex/delta_converter.ex"],"programRoutines":[{"name":"'Elixir.MDEx':to_delta/2"},{"name":"'Elixir.MDEx.DeltaConverter':convert/2"},{"name":"'Elixir.MDEx.DeltaConverter':default_convert_node/3"}],"repo":"https://github.com/leandrocp/mdex","packageURL":"pkg:github/leandrocp/mdex","versions":[{"version":"9852db2456fdc9d856eb636603a7f608e22e3793","lessThan":"2817147f5b87ce7186aa604c9ee72499485b8f2f","versionType":"git","status":"affected"}]}]