' 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.","datePublished":"2026-06-29T18:50:17.185Z","dateModified":"2026-06-29T19:06:33.949Z","url":"https://radar.offseq.com/threat/cve-2026-53427-cwe-79-improper-neutralization-of-i-de870c8fb7422501","author":{"@type":"Organization","name":"OffSeq Threat Intelligence","url":"https://radar.offseq.com"},"publisher":{"@type":"Organization","name":"OffSeq","logo":{"@type":"ImageObject","url":"https://radar.offseq.com/favicon.png"}},"mainEntityOfPage":{"@type":"WebPage","@id":"https://radar.offseq.com/threat/cve-2026-53427-cwe-79-improper-neutralization-of-i-de870c8fb7422501"},"identifier":"CVE-2026-53427","contentRating":"LOW","keywords":"cve,cve-2026-53427,cwe-79"}
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CVE-2026-53427: CWE-79 Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') in leandrocp mdex

0
Low
VulnerabilityCVE-2026-53427cvecve-2026-53427cwe-79
Published: 06/29/2026 (06/29/2026, 18:50:17 UTC)
Source: CVE Database V5
Vendor/Project: leandrocp
Product: mdex

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.

CVSS v4.0

Score 2.3low

Attack Vector
Network
Attack Complexity
Low
Attack Requirements
Present
Privileges Required
None
User Interaction
Passive
Vuln. Confidentiality
None
Vuln. Integrity
None
Vuln. Availability
None
Subsq. Confidentiality
Low
Subsq. Integrity
Low
Subsq. Availability
None
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

Affected software

mdex
pkg:hex/mdex
Affected versions
>=0.11.3 <0.12.3
GitHub Actionsmore threats →cve
leandrocp/mdex
pkg:github/leandrocp/mdex
mdex_native
pkg:hex/mdex_native
Affected versions
>=0.1.0 <0.2.3
GitHub Actionsmore threats →cve
leandrocp/mdex_native
pkg:github/leandrocp/mdex_native
CPE configurations (2)
cpe:2.3:a:leandrocp:mdex:*:*:*:*:*:*:*:*
cpe:2.3:a:leandrocp:mdex_native:*:*:*:*:*:*:*:*

Run on your own infrastructure? Check whether these packages are installed with threat-finder — our free open-source scanner.

Technical Details

Data Version
5.2
Assigner Short Name
EEF
Date Reserved
2026-06-09T11:01:47.529Z
Cvss Version
4.0
State
PUBLISHED
Remediation Level
null

Threat ID: 6a42c23927e9c79719595bfe

Added to database: 06/29/2026, 19:06:33 UTC

Last updated: 06/29/2026, 19:06:33 UTC

Views: 1

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