EUVD-2026-262278

fkie_cve-2025-66400

mdast-util-to-hast is an mdast utility to transform to hast. From 13.0.0 to before 13.2.1, 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. This vulnerability is fixed in 13.2.1.

GHSA-4fh9-h7wg-q85m — mdast-util-to-hast has unsanitized class attribute

Affected: npm: mdast-util-to-hast

### 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 `<pre><code class="language-js xss"></code></pre>` If your page then applied `.xss` classes (or listeners in JS), those apply to this element. For more info see <https://github.com/ChALkeR/notes/blob/master/Improper-markup-sanitization.md#unsanitized-class-attribute>

### 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

Most recent entries from all

EUVD-2026-262278

fkie_cve-2025-66400

GHSA-4fh9-h7wg-q85m — mdast-util-to-hast has unsanitized class attribute