BaseFortify

Publication date: 2025-12-01

Last updated on: 2026-02-06

Assigner: GitHub, Inc.

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.

CVSS Scores

EPSS Scores

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Meta Information

Published

2025-12-01

Last Modified

2026-02-06

Generated

2026-07-06

AI Q&A

2025-12-02

EPSS Evaluated

2026-07-05

NVD

CVE-2025-66400

Affected Vendors & Products

Vendor	Product	Version / Range
syntax-tree	mdast-util-to-hast	From 13.0.0 (inc) to 13.2.1 (inc)
unifiedjs	mdast-util-to-hast	From 13.0.0 (inc) to 13.2.1 (inc)
mdast-util	mdast-util-to-hast	13.2.1
mdast-util	mdast-util-to-hast	13.0.0

Helpful Resources

Exploitability

CWE

KEV

CWE ID	Description
CWE-20	The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly.
CWE-915	The product receives input from an upstream component that specifies multiple attributes, properties, or fields that are to be initialized or updated in an object, but it does not properly control which attributes can be modified.

Attack-Flow Graph

Executive Summary

This vulnerability in mdast-util-to-hast versions from 13.0.0 to before 13.2.1 allows multiple unprefixed classnames to be added in markdown source by using character references. This means that user-supplied markdown code elements could be made to appear like the rest of the page, potentially misleading users about the origin or nature of the content. The issue was fixed in version 13.2.1.

Impact Analysis

The vulnerability could allow an attacker to manipulate the appearance of user-supplied markdown code elements so that they look like legitimate parts of the page. This could lead to confusion or deception, potentially enabling phishing or other social engineering attacks by making malicious content appear trustworthy or integrated with the rest of the page.

Mitigation Strategies

Update mdast-util-to-hast to version 13.2.1 or later, as this version contains the fix for the vulnerability.

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