CVE-2025-66400

low-risk
Published 2025-12-01

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.

Do I need to act?

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0.09% chance of exploitation
EPSS score — low exploit probability
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Not on CISA KEV list
No confirmed active exploitation reported to CISA
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Patch status unknown
Check vendor advisories for fix availability and mitigation guidance
5
CVSS 5.3/10 Medium
NETWORK / LOW complexity

Affected Products (1)

Mdast-Util-To-Hast

Affected Vendors

Unifiedjs

References (3)

Patch https://github.com/syntax-tree/mdast-util-to-hast/commit/6fc783ae6abdeb798fd5a68...
Patch https://github.com/syntax-tree/mdast-util-to-hast/commit/ab3a79570a1afbfa7efef5d...
Vendor Advisory https://github.com/syntax-tree/mdast-util-to-hast/security/advisories/GHSA-4fh9-...
26
/ 100
low-risk
Severity 21/34 · High
Exploitability 0/34 · Minimal
Exposure 5/34 · Minimal