How severe is CVE-2025-66400?

CVE-2025-66400 has a CVSS 3.x base score of 5.3, rated medium severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity low, and availability none.

Is CVE-2025-66400 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (17th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2025-66400?

CVE-2025-66400 affects Unifiedjs Mdast-util-to-hast. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2025-66400?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.

Does CVE-2025-66400 have an EU (EUVD) identifier?

Yes. CVE-2025-66400 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2025-200113.

When was CVE-2025-66400 published?

CVE-2025-66400 was published on 2025-12-01 and last updated on 2026-06-17.

CVE-2025-66400

CVE-2025-66400 is a medium-severity vulnerability in Unifiedjs Mdast-util-to-hast with a CVSS 3.x base score of 5.3. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-20.

Key facts

Severity: Medium (CVSS 3.x base score 5.3)
CVSS v4: 6.9
EPSS exploit prediction: 0% (17th percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2025-200113
Weakness: CWE-20
Affected product: Unifiedjs Mdast-util-to-hast
Published: 2025-12-01
Last modified: 2026-06-17

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.

Frequently asked questions

What is CVE-2025-66400?: 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.
How severe is CVE-2025-66400?: CVE-2025-66400 has a CVSS 3.x base score of 5.3, rated medium severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity low, and availability none.
Is CVE-2025-66400 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (17th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2025-66400?: CVE-2025-66400 affects Unifiedjs Mdast-util-to-hast. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2025-66400?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
Does CVE-2025-66400 have an EU (EUVD) identifier?: Yes. CVE-2025-66400 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2025-200113.
When was CVE-2025-66400 published?: CVE-2025-66400 was published on 2025-12-01 and last updated on 2026-06-17.

References

Affected products (1)

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

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