Vulnerability · Published Dec 1, 2025 · Assigned by GitHub_M

CVE-2025-66400mdast-util-to-hast unsanitized class attribute

Medium 6.9

In plain English

A medium-severity improper input validation in mdast-util-to-hast from syntax-tree. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.3% (higher than 26% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 4.0)6.9Medium

Exploit odds (30 days)0.3%top 74.1% of all CVEs

Exploited in the wildNo reportsCISA SSVC: none

Attack toolingNoneno public tooling known

Official description

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.

Affected packages & fixed versions

Ecosystem	Package	Fixed in	Advisory
npm	mdast-util-to-hast	13.2.1	GHSA-4fh9-h7wg-q85m

Affected products (as reported)

Vendor	Product	Versions
syntax-tree	mdast-util-to-hast	>= 13.0.0, < 13.2.1

Weakness: CWE-20, CWE-915 · Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N

References

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