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