{"id":"EEF-CVE-2026-54889","summary":"Unsanitized URL schemes in MDEx Quill Delta output allow javascript: injection (XSS)","details":"## Summary\n\nImproper Neutralization of Input During Web Page Generation (XSS) vulnerability in leandrocp mdex allows cross-site scripting via unsanitized URL schemes in Quill Delta output.\n\n'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.\n\nAn 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 \u003ca href\u003e or \u003cimg src\u003e, 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 \u003cimg src\u003e generally does not execute in modern browsers.\n\nThis issue affects mdex: from 0.8.3 before 0.13.2.\n\n## Workaround\n\nSanitize the Quill Delta produced by 'Elixir.MDEx':to\\_delta/2 before rendering it: drop or blank any \"link\" or \"image\" value whose URL scheme is not in a safe allowlist (http, https, mailto, tel).\n\n## Configuration\n\nThe application must pass untrusted Markdown to 'Elixir.MDEx':to\\_delta/2 and then render the resulting Quill Delta to HTML with a renderer that maps the \"link\" and \"image\" attributes to href and src without applying its own URL scheme sanitization (for example quill-delta-to-html or the Quill client).","aliases":["CVE-2026-54889","GHSA-4383-7xfp-gpph"],"modified":"2026-06-30T04:38:42.158Z","published":"2026-06-29T19:10:49.841Z","database_specific":{"cwe_ids":["CWE-79"],"cpe_ids":["cpe:2.3:a:leandrocp:mdex:*:*:*:*:*:*:*:*"],"capec_ids":["CAPEC-244"]},"references":[{"type":"ADVISORY","url":"https://github.com/leandrocp/mdex/security/advisories/GHSA-4383-7xfp-gpph"},{"type":"WEB","url":"https://cna.erlef.org/cves/CVE-2026-54889.html"},{"type":"FIX","url":"https://github.com/leandrocp/mdex/commit/2817147f5b87ce7186aa604c9ee72499485b8f2f"},{"type":"PACKAGE","url":"https://hex.pm/packages/mdex"}],"affected":[{"package":{"name":"mdex","ecosystem":"Hex","purl":"pkg:hex/mdex"},"ranges":[{"type":"SEMVER","events":[{"introduced":"0.8.3"},{"fixed":"0.13.2"}]}],"versions":["0.10.0","0.11.0","0.11.1","0.11.2","0.11.3","0.11.4","0.11.5","0.11.6","0.11.7","0.12.0","0.12.1","0.12.2","0.12.3","0.12.4","0.12.5","0.13.0","0.13.1","0.8.3","0.8.4","0.8.5","0.8.6","0.9.0","0.9.1","0.9.2","0.9.3","0.9.4"],"database_specific":{"source":"https://cna.erlef.org/osv/EEF-CVE-2026-54889.json"}},{"ranges":[{"type":"GIT","repo":"https://github.com/leandrocp/mdex","events":[{"introduced":"9852db2456fdc9d856eb636603a7f608e22e3793"},{"fixed":"2817147f5b87ce7186aa604c9ee72499485b8f2f"}]}],"versions":["v0.13.1","v0.13.0","v0.12.5","v0.12.4","v0.12.3","v0.12.2","v0.12.1","v0.12.0","v0.11.7","v0.11.6","v0.11.5","v0.11.4","v0.11.3","v0.11.2","v0.11.1","v0.11.0","v0.10.0","v0.9.4","v0.9.3","v0.9.2","v0.9.1","v0.9.0","v0.8.6","v0.8.5","v0.8.4","v0.8.3"],"database_specific":{"source":"https://cna.erlef.org/osv/EEF-CVE-2026-54889.json"}}],"schema_version":"1.7.5","severity":[{"type":"CVSS_V4","score":"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:A/VC:L/VI:L/VA:N/SC:L/SI:L/SA:N"}],"credits":[{"name":"Peter Ullrich","type":"FINDER"},{"name":"Leandro Pereira","type":"REMEDIATION_DEVELOPER"},{"name":"Jonatan Männchen / EEF","type":"ANALYST"}]}