GitHub Advisoryadvisory · npm
GHSA-4fh9-h7wg-q85m mdast-util-to-hast has unsanitized class attribute
MEDIUM
Official page ↗
- Aliases
- CVE-2025-66400
- Ecosystem
- npm
- Packages
- mdast-util-to-hast
- Severity
- Moderate
- CVSS vector
- CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
- Weaknesses
- CWE-20, CWE-915
- Reviewed
- 2025-12-02
Affected packages
• npm mdast-util-to-hast: >= 13.0.0, < 13.2.1 → fixed in 13.2.1
Description
Impact
Multiple (unprefixed) classnames could be added in markdown source by using character references.
This could make rendered user supplied markdown `code` elements appear like the rest of the page.
The following markdown:
````markdown
```js xss
```
````
Would create ``
If your page then applied `.xss` classes (or listeners in JS), those apply to this element.
For more info see
Patches
The bug was patched. When using regular semver, run `npm install`. For exact ranges, make sure to use `13.2.1`.
Workarounds
Update.
References
• bug introduced in https://github.com/syntax-tree/mdast-util-to-hast/commit/6fc783ae6abdeb798fd5a68e7f3f21411dde7403
• bug fixed in https://github.com/syntax-tree/mdast-util-to-hast/commit/ab3a79570a1afbfa7efef5d4a0cd9b5caafbc5d7
Related
Alias · CVE (1)
- CVE-2025-66400 mdast-util-to-hast is an mdast utility to transform to hast. vulnerability
References
- https://github.com/syntax-tree/mdast-util-to-hast/security/advisories/GHSA-4fh9-h7wg-q85m web
- https://nvd.nist.gov/vuln/detail/CVE-2025-66400 advisory
- https://github.com/syntax-tree/mdast-util-to-hast/commit/6fc783ae6abdeb798fd5a68e7f3f21411dde7403 web
- https://github.com/syntax-tree/mdast-util-to-hast/commit/ab3a79570a1afbfa7efef5d4a0cd9b5caafbc5d7 web
- https://github.com/syntax-tree/mdast-util-to-hast package