Vulnerability-Lookup

GHSA-4FH9-H7WG-Q85M

Vulnerability from github – Published: 2025-12-02 01:25 – Updated: 2026-02-06 19:00

Summary

mdast-util-to-hast has unsanitized class attribute

Details

Impact

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. The following markdown:

```js&#x20;xss
```

Would create <pre><code class="language-js xss"></code></pre> If your page then applied .xss classes (or listeners in JS), those apply to this element. For more info see https://github.com/ChALkeR/notes/blob/master/Improper-markup-sanitization.md#unsanitized-class-attribute

Patches

The bug was patched. When using regular semver, run npm install. For exact ranges, make sure to use 13.2.1.

Workarounds

Update.

References

bug introduced in https://github.com/syntax-tree/mdast-util-to-hast/commit/6fc783ae6abdeb798fd5a68e7f3f21411dde7403
bug fixed in https://github.com/syntax-tree/mdast-util-to-hast/commit/ab3a79570a1afbfa7efef5d4a0cd9b5caafbc5d7

Severity

5.3 (Medium)


                  
                    CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N

6.9 (Medium)


                  
                    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

Show details on source website

JSON

To clipboard

{
  "affected": [
    {
      "package": {
        "ecosystem": "npm",
        "name": "mdast-util-to-hast"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "13.0.0"
            },
            {
              "fixed": "13.2.1"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2025-66400"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-20",
      "CWE-915"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2025-12-02T01:25:46Z",
    "nvd_published_at": "2025-12-01T23:15:53Z",
    "severity": "MODERATE"
  },
  "details": "### Impact\n\nMultiple (unprefixed) classnames could be added in markdown source by using character references.\nThis could make rendered user supplied markdown `code` elements appear like the rest of the page.\nThe following markdown:\n\n````markdown\n```js\u0026#x20;xss\n```\n````\n\nWould create `\u003cpre\u003e\u003ccode class=\"language-js xss\"\u003e\u003c/code\u003e\u003c/pre\u003e`\nIf your page then applied `.xss` classes (or listeners in JS), those apply to this element.\nFor more info see \u003chttps://github.com/ChALkeR/notes/blob/master/Improper-markup-sanitization.md#unsanitized-class-attribute\u003e\n\n### Patches\n\nThe bug was patched. When using regular semver, run `npm install`. For exact ranges, make sure to use `13.2.1`.\n\n### Workarounds\n\nUpdate.\n\n### References\n\n* bug introduced in https://github.com/syntax-tree/mdast-util-to-hast/commit/6fc783ae6abdeb798fd5a68e7f3f21411dde7403\n* bug fixed in https://github.com/syntax-tree/mdast-util-to-hast/commit/ab3a79570a1afbfa7efef5d4a0cd9b5caafbc5d7",
  "id": "GHSA-4fh9-h7wg-q85m",
  "modified": "2026-02-06T19:00:13Z",
  "published": "2025-12-02T01:25:46Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/syntax-tree/mdast-util-to-hast/security/advisories/GHSA-4fh9-h7wg-q85m"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2025-66400"
    },
    {
      "type": "WEB",
      "url": "https://github.com/syntax-tree/mdast-util-to-hast/commit/6fc783ae6abdeb798fd5a68e7f3f21411dde7403"
    },
    {
      "type": "WEB",
      "url": "https://github.com/syntax-tree/mdast-util-to-hast/commit/ab3a79570a1afbfa7efef5d4a0cd9b5caafbc5d7"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/syntax-tree/mdast-util-to-hast"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N",
      "type": "CVSS_V3"
    },
    {
      "score": "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",
      "type": "CVSS_V4"
    }
  ],
  "summary": "mdast-util-to-hast has unsanitized class attribute"
}

CVE-2025-66400 (GCVE-0-2025-66400)

Vulnerability from cvelistv5 – Published: 2025-12-01 22:17 – Updated: 2025-12-02 15:34

Title

mdast-util-to-hast unsanitized class attribute

Summary

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.

Severity

6.9 (Medium)


                        
                          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

SSVC

Exploitation: none Automatable: yes Technical Impact: partial

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2025-12-02 15:34 UTC

CWE

CWE-20 - Improper Input Validation
CWE-915 - Improperly Controlled Modification of Dynamically-Determined Object Attributes

Assigner

GitHub_M mitre root

References

3 references

URL	Tags
https://github.com/syntax-tree/mdast-util-to-hast…	x_refsource_CONFIRM
https://github.com/syntax-tree/mdast-util-to-hast…	x_refsource_MISC
https://github.com/syntax-tree/mdast-util-to-hast…	x_refsource_MISC

Impacted products

1 product

Vendor	Product	Version
syntax-tree	mdast-util-to-hast	Affected: >= 13.0.0, < 13.2.1

Show details on NVD website

JSON

To clipboard

{
  "containers": {
    "adp": [
      {
        "metrics": [
          {
            "other": {
              "content": {
                "id": "CVE-2025-66400",
                "options": [
                  {
                    "Exploitation": "none"
                  },
                  {
                    "Automatable": "yes"
                  },
                  {
                    "Technical Impact": "partial"
                  }
                ],
                "role": "CISA Coordinator",
                "timestamp": "2025-12-02T15:34:16.267018Z",
                "version": "2.0.3"
              },
              "type": "ssvc"
            }
          }
        ],
        "providerMetadata": {
          "dateUpdated": "2025-12-02T15:34:24.293Z",
          "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
          "shortName": "CISA-ADP"
        },
        "title": "CISA ADP Vulnrichment"
      }
    ],
    "cna": {
      "affected": [
        {
          "product": "mdast-util-to-hast",
          "vendor": "syntax-tree",
          "versions": [
            {
              "status": "affected",
              "version": "\u003e= 13.0.0, \u003c 13.2.1"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "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."
        }
      ],
      "metrics": [
        {
          "cvssV4_0": {
            "attackComplexity": "LOW",
            "attackRequirements": "NONE",
            "attackVector": "NETWORK",
            "baseScore": 6.9,
            "baseSeverity": "MEDIUM",
            "privilegesRequired": "NONE",
            "subAvailabilityImpact": "NONE",
            "subConfidentialityImpact": "NONE",
            "subIntegrityImpact": "NONE",
            "userInteraction": "NONE",
            "vectorString": "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",
            "version": "4.0",
            "vulnAvailabilityImpact": "NONE",
            "vulnConfidentialityImpact": "NONE",
            "vulnIntegrityImpact": "LOW"
          }
        }
      ],
      "problemTypes": [
        {
          "descriptions": [
            {
              "cweId": "CWE-20",
              "description": "CWE-20: Improper Input Validation",
              "lang": "en",
              "type": "CWE"
            }
          ]
        },
        {
          "descriptions": [
            {
              "cweId": "CWE-915",
              "description": "CWE-915: Improperly Controlled Modification of Dynamically-Determined Object Attributes",
              "lang": "en",
              "type": "CWE"
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2025-12-01T22:17:42.705Z",
        "orgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
        "shortName": "GitHub_M"
      },
      "references": [
        {
          "name": "https://github.com/syntax-tree/mdast-util-to-hast/security/advisories/GHSA-4fh9-h7wg-q85m",
          "tags": [
            "x_refsource_CONFIRM"
          ],
          "url": "https://github.com/syntax-tree/mdast-util-to-hast/security/advisories/GHSA-4fh9-h7wg-q85m"
        },
        {
          "name": "https://github.com/syntax-tree/mdast-util-to-hast/commit/6fc783ae6abdeb798fd5a68e7f3f21411dde7403",
          "tags": [
            "x_refsource_MISC"
          ],
          "url": "https://github.com/syntax-tree/mdast-util-to-hast/commit/6fc783ae6abdeb798fd5a68e7f3f21411dde7403"
        },
        {
          "name": "https://github.com/syntax-tree/mdast-util-to-hast/commit/ab3a79570a1afbfa7efef5d4a0cd9b5caafbc5d7",
          "tags": [
            "x_refsource_MISC"
          ],
          "url": "https://github.com/syntax-tree/mdast-util-to-hast/commit/ab3a79570a1afbfa7efef5d4a0cd9b5caafbc5d7"
        }
      ],
      "source": {
        "advisory": "GHSA-4fh9-h7wg-q85m",
        "discovery": "UNKNOWN"
      },
      "title": "mdast-util-to-hast unsanitized class attribute"
    }
  },
  "cveMetadata": {
    "assignerOrgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
    "assignerShortName": "GitHub_M",
    "cveId": "CVE-2025-66400",
    "datePublished": "2025-12-01T22:17:42.705Z",
    "dateReserved": "2025-11-28T23:33:56.364Z",
    "dateUpdated": "2025-12-02T15:34:24.293Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}

Sightings

Author	Source	Type	Date	Other

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.

Related by attack behaviour

Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.

Action not permitted

GHSA-4FH9-H7WG-Q85M

Impact

Patches

Workarounds

References

CVE-2025-66400 (GCVE-0-2025-66400)

Tags

Sightings

Nomenclature

Related by attack behaviour