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.

CVSS 4.0

6.9CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N

CVSS 3.1

5.3CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N

EPSS

0.3% chance of exploitation in the next 30 days; higher than 23% of CVEs (scores of 2026-10-25)

CWEs

CWE-20, CWE-915

Published

2025-12-01

Modified

2026-10-18

Record from

the NVD, synced 2026-10-19

Affected

• unifiedjs:mdast-util-to-hast

Packages (OSV)

References

• https://github.com/syntax-tree/mdast-util-to-hast/commit/6fc783ae6abdeb798fd5a68e7f3f21411dde7403
• https://github.com/syntax-tree/mdast-util-to-hast/commit/ab3a79570a1afbfa7efef5d4a0cd9b5caafbc5d7
• https://github.com/syntax-tree/mdast-util-to-hast/security/advisories/GHSA-4fh9-h7wg-q85m

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