{"id":"CVE-2026-53427","summary":"Cross-site scripting in MDEx via unescaped highlight_lines_class code-fence attribute","details":"Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') vulnerability in leandrocp MDEx allows stored or reflected cross-site scripting via attacker-controlled Markdown.\n\nWhen syntax highlighting and full info-string forwarding (render: [full_info_string: true]) are enabled, the Lumis adapter copies the value of a code fence's highlight_lines_class info-string attribute, unescaped, into the class attribute of every rendered line. comrak_nif::lumis_adapter::LumisAdapter::parse_custom_attributes in native/comrak_nif/src/lumis_adapter.rs shlex-parses the info string and stores each key=value pair verbatim, highlight_lines_config pulls highlight_lines_class into the per-line class value, and write_highlighted interpolates that value directly into the class attribute of the per-line \u003cdiv\u003e. A single-quoted shell token preserves an inner double quote through shlex parsing, so a value such as '\"\u003e\u003cscript\u003ealert(1)\u003c/script\u003e' terminates the class attribute early and the markup that follows is emitted as live HTML.\n\nAn attacker who can submit Markdown (through comments, posts, wiki pages, documentation, or any user-generated content) can inject arbitrary HTML and JavaScript that runs in the browser of every user who views the rendered output, enabling session theft, account takeover, and other client-side attacks. No authentication or special privileges are required.\n\nThe vulnerable native code originally shipped inside mdex (in native/comrak_nif/src/lumis_adapter.rs) and was later extracted into the separate mdex_native package (native/mdex_native_nif/src/lumis_adapter.rs), where it remains unpatched.\n\nThis issue affects mdex from 0.11.3 before 0.12.3, and mdex_native from 0.1.0 before 0.2.3.","aliases":["EEF-CVE-2026-53427","GHSA-v664-pmxr-mxxx"],"modified":"2026-07-11T03:54:30.198317822Z","published":"2026-06-29T18:50:17.185Z","database_specific":{"cna_assigner":"EEF","cwe_ids":["CWE-79"],"osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/53xxx/CVE-2026-53427.json","unresolved_ranges":[{"extracted_events":[{"introduced":"0d7ffc84ea742e1daf666426814e5bb6d0499433"},{"fixed":"6ed94d905f97af188323f042698ae841c02293b4"},{"introduced":"956528c5e31746253347029e810a969ab916fd27"},{"fixed":"798a363b4339f6f7162ec8437c4c9f9b5ae6fbf3"}],"source":"AFFECTED_FIELD"}]},"references":[{"type":"WEB","url":"https://cna.erlef.org/cves/CVE-2026-53427.html"},{"type":"WEB","url":"https://github.com"},{"type":"WEB","url":"https://osv.dev/vulnerability/EEF-CVE-2026-53427"},{"type":"WEB","url":"https://repo.hex.pm"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/53xxx/CVE-2026-53427.json"},{"type":"ADVISORY","url":"https://github.com/leandrocp/mdex_native/security/advisories/GHSA-v664-pmxr-mxxx"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-53427"},{"type":"FIX","url":"https://github.com/leandrocp/mdex_native/commit/798a363b4339f6f7162ec8437c4c9f9b5ae6fbf3"},{"type":"PACKAGE","url":"https://github.com/leandrocp/mdex"},{"type":"PACKAGE","url":"https://github.com/leandrocp/mdex_native"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://github.com/leandrocp/mdex","events":[{"introduced":"6330432e88e75bf98eb91546a5aef13dffd637bb"},{"fixed":"2cb9eb2f6014414b40c8f1e5d5181b9692626c38"}],"database_specific":{"extracted_events":[{"introduced":"0.11.3"},{"fixed":"0.12.3"}],"source":"AFFECTED_FIELD"}},{"type":"GIT","repo":"https://github.com/leandrocp/mdex_native","events":[{"introduced":"0"},{"fixed":"b6caf84e9dd035654ed7e8955086ab37afdaa7a0"},{"fixed":"798a363b4339f6f7162ec8437c4c9f9b5ae6fbf3"}],"database_specific":{"extracted_events":[{"introduced":"0.1.0"},{"fixed":"0.2.3"}],"source":["DESCRIPTION","REFERENCES"]}}],"versions":["v0.12.2","v0.12.1","v0.12.0","v0.11.7","v0.11.6","v0.11.5","v0.11.4","v0.11.3","v0.2.2","v0.2.1","v0.2.0","v0.1.5","v0.1.4","v0.1.3","v0.1.2","v0.1.1"],"database_specific":{"source":"https://storage.googleapis.com/osv-test-cve-osv-conversion/osv-output/CVE-2026-53427.json"}}],"schema_version":"1.7.5","severity":[{"type":"CVSS_V4","score":"CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N"}]}