When 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 <div>. A single-quoted shell token preserves an inner double quote through shlex parsing, so a value such as '"><script>alert(1)</script>' terminates the class attribute early and the markup that follows is emitted as live HTML.
An 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.
The 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.
This issue affects mdex from 0.11.3 before 0.12.3, and mdex_native from 0.1.0 before 0.2.3.
Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).
| Vendor | Product | Default status | Versions | ||||||
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| leandrocp | mdex | unaffected |
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| leandrocp | mdex | unaffected |
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| leandrocp | mdex_native | unaffected |
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| leandrocp | mdex_native | unaffected |
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Solution
No solution given by the vendor.
Workaround
Do not enable full info-string forwarding (render: [full_info_string: true]) when rendering untrusted Markdown, which prevents the highlight_lines_class attribute from reaching the highlighter. Alternatively, restrict highlight_lines_class values to a safe character set (for example [A-Za-z0-9_- ]) before rendering.
Mon, 29 Jun 2026 20:30:00 +0000
| Type | Values Removed | Values Added |
|---|---|---|
| Metrics |
ssvc
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Mon, 29 Jun 2026 19:00:00 +0000
| Type | Values Removed | Values Added |
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| Description | 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. When 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 <div>. A single-quoted shell token preserves an inner double quote through shlex parsing, so a value such as '"><script>alert(1)</script>' terminates the class attribute early and the markup that follows is emitted as live HTML. An 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. The 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. This issue affects mdex from 0.11.3 before 0.12.3, and mdex_native from 0.1.0 before 0.2.3. | |
| Title | Cross-site scripting in MDEx via unescaped highlight_lines_class code-fence attribute | |
| First Time appeared |
Leandrocp
Leandrocp mdex Leandrocp mdex Native |
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| Weaknesses | CWE-79 | |
| CPEs | cpe:2.3:a:leandrocp:mdex:*:*:*:*:*:*:*:* cpe:2.3:a:leandrocp:mdex_native:*:*:*:*:*:*:*:* |
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| Vendors & Products |
Leandrocp
Leandrocp mdex Leandrocp mdex Native |
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| References |
| |
| Metrics |
cvssV4_0
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Projects
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MITRE
Status: PUBLISHED
Assigner: EEF
Published:
Updated: 2026-06-29T19:19:28.028Z
Reserved: 2026-06-09T11:01:47.529Z
Link: CVE-2026-53427
Vulnrichment
Updated: 2026-06-29T19:19:09.581Z
NVD
No data.
Redhat
No data.
OpenCVE Enrichment
Updated: 2026-06-29T20:30:03Z