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.

Attack Vector Network

Attack Complexity Low

Privileges Required None

Attack Requirements None

User Interaction None

Vulnerable System Confidentiality Impact None

Vulnerable System Integrity Impact Low

Vulnerable System Availability Impact None

Subsequent System Confidentiality Impact None

Subsequent System Integrity Impact None

Subsequent System Availability Impact None

Attack Vector Network

Attack Complexity Low

Privileges Required None

Scope Unchanged

Confidentiality Impact None

Integrity Impact Low

Availability Impact None

User Interaction None

No CVSS v3.0

No CVSS v2

This CVE is not in the KEV list.

The EPSS score is 0.00076.

Exploitation none

Automatable yes

Technical Impact partial

Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).

Vendor Product Default status Versions
syntax-tree mdast-util-to-hast affected
Version Status Constraints
>= 13.0.0, < 13.2.1 affected —

Configuration 1 [-]

cpe:2.3:a:unifiedjs:mdast-util-to-hast:*:*:*:*:*:node.js:*:*

No data.

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Vendors Products
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Project Subscriptions

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Unifiedjs Subscribe
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Advisories
Source ID Title
Github GHSA Github GHSA GHSA-4fh9-h7wg-q85m mdast-util-to-hast has unsanitized class attribute
Fixes

Solution

No solution given by the vendor.

Workaround

No workaround given by the vendor.

References
Link Providers
https://github.com/syntax-tree/mdast-util-to-hast/commit/6fc783ae6abdeb798fd5a68e7f3f21411dde7403 cve-icon cve-icon cve-icon
https://github.com/syntax-tree/mdast-util-to-hast/commit/ab3a79570a1afbfa7efef5d4a0cd9b5caafbc5d7 cve-icon cve-icon cve-icon
https://github.com/syntax-tree/mdast-util-to-hast/security/advisories/GHSA-4fh9-h7wg-q85m cve-icon cve-icon cve-icon
https://nvd.nist.gov/vuln/detail/CVE-2025-66400 cve-icon
https://www.cve.org/CVERecord?id=CVE-2025-66400 cve-icon
History

Fri, 06 Feb 2026 16:45:00 +0000

Type Values Removed Values Added
First Time appeared Unifiedjs
Unifiedjs mdast-util-to-hast
CPEs cpe:2.3:a:syntax-tree:mdast-util-to-hast:*:*:*:*:*:*:*:* cpe:2.3:a:unifiedjs:mdast-util-to-hast:*:*:*:*:*:node.js:*:*
Vendors & Products Unifiedjs
Unifiedjs mdast-util-to-hast

Fri, 06 Feb 2026 16:30:00 +0000

Type Values Removed Values Added
Weaknesses NVD-CWE-Other
CPEs cpe:2.3:a:syntax-tree:mdast-util-to-hast:*:*:*:*:*:*:*:*

Wed, 17 Dec 2025 12:15:00 +0000

Type Values Removed Values Added
References
Metrics threat_severity

None

 cvssV3_1

{'score': 5.3, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N'}

threat_severity

Moderate

Thu, 04 Dec 2025 18:15:00 +0000

Type Values Removed Values Added
First Time appeared Syntax-tree
Syntax-tree mdast-util-to-hast
Vendors & Products Syntax-tree
Syntax-tree mdast-util-to-hast

Tue, 02 Dec 2025 16:15:00 +0000

Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'yes', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}

Mon, 01 Dec 2025 22:30:00 +0000

Type Values Removed Values Added
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.
Title mdast-util-to-hast unsanitized class attribute
Weaknesses CWE-20
CWE-915
References
Metrics cvssV4_0

{'score': 6.9, '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'}

Projects

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cve-icon MITRE

Status: PUBLISHED

Assigner: GitHub_M

Published:

Updated: 2025-12-02T15:34:24.293Z

Reserved: 2025-11-28T23:33:56.364Z

Link: CVE-2025-66400

cve-icon Vulnrichment

Updated: 2025-12-02T15:34:19.930Z

cve-icon NVD

Status : Analyzed

Published: 2025-12-01T23:15:53.070

Modified: 2026-02-06T16:36:19.913

Link: CVE-2025-66400

cve-icon Redhat

Severity : Moderate

Publid Date: 2025-12-01T22:17:42Z

Links: CVE-2025-66400 - Bugzilla

cve-icon OpenCVE Enrichment

Updated: 2025-12-04T18:07:15Z

Weaknesses