CVE-2025-66400

mdast-util-to-hast unsanitized class attribute

CVSS 6.9 MEDIUMEPSS 0.3%CWE-20 CWE-915

Vexday Risk Score

13Low

SSVC decision (CISA)

Track

No exploitation signal → monitor

CVSS 6.9EPSS 0.3%KEV nãoPoC —Nuclei —Metasploit —Patch —

Lifecycle

01 Dec 2025Published on NVD

Recommendation: Monitor — no exploitation signal at the moment.

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

Affected products

syntax-tree · mdast-util-to-hast

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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