Security: Cross-Site Scripting (XSS) via unsanitized Markdown-to-HTML injection#626
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The fetched Markdown content from GitHub is parsed by `marked.parse()` and directly assigned to `innerHTML` without any sanitization (e.g., DOMPurify). The `marked` library does not sanitize embedded HTML in Markdown by default. An attacker who can modify the README.md (e.g., via a malicious pull request) could inject arbitrary HTML such as `<img src=x onerror='...'>` which would execute JavaScript in visitors' browsers. Affected files: index.html Signed-off-by: Trần Bách <45133811+barttran2k@users.noreply.github.com>
offa
reviewed
Apr 7, 2026
| <!-- Marked plugin to add heading ID's --> | ||
| <script src="https://cdn.jsdelivr.net/npm/marked-gfm-heading-id/lib/index.umd.js"></script> | ||
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| <!-- DOMPurify to sanitize parsed HTML --> |
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In reference to #625, shouldn't this version be pinned here as well?
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Problem
The fetched Markdown content from GitHub is parsed by
marked.parse()and directly assigned toinnerHTMLwithout any sanitization (e.g., DOMPurify). Themarkedlibrary does not sanitize embedded HTML in Markdown by default. An attacker who can modify the README.md (e.g., via a malicious pull request) could inject arbitrary HTML such as<img src=x onerror='...'>which would execute JavaScript in visitors' browsers.Severity:
highFile:
index.htmlSolution
Sanitize the parsed HTML before injecting it into the DOM. Use DOMPurify:
document.querySelector('main').innerHTML = DOMPurify.sanitize(marked.parse(data));and add<script src="https://cdn.jsdelivr.net/npm/dompurify/dist/purify.min.js" integrity="..." crossorigin="anonymous"></script>.Changes
index.html(modified)Testing