CVE-2025-66400

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&#x20;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

How to fix CVE-2025-66400

To remediate CVE-2025-66400, upgrade the affected package to a fixed version below.

• —upgrade to 13.2.1 or later

Is CVE-2025-66400 being exploited?

Low — EPSS is 0.1%, meaning exploitation activity has not been observed at scale.

Affected packages (1)

• >= 13.0.0, < 13.2.1

CVSS scores

References (5)

• ADVISORYnvd.nist.gov/vuln/detail/CVE-2025-66400
• PATCHgithub.com/syntax-tree/mdast-util-to-hast
• WEBgithub.com/syntax-tree/mdast-util-to-hast/commit/6fc783ae6abdeb798fd5a68e7f3f21411dde7403
• WEBgithub.com/syntax-tree/mdast-util-to-hast/commit/ab3a79570a1afbfa7efef5d4a0cd9b5caafbc5d7