# CVE-2026-126365: Astro: XSS via unescaped code for unsupported languages in @astrojs/prism

Status: published. Published: 2026-11-12. Updated: 2026-11-12.

Astro is a web framework for content-driven websites. Prior to @astrojs/prism 4.1.2, and from @astrojs/markdoc 0.3.0 until 2.1.2, runHighlighterWithAstro() returned code unchanged when Prism had no grammar for the requested language, and callers inserted that result as raw HTML. A code block labeled with an unsupported language could therefore render embedded HTML and script instead of displaying it as text. The Prism component was affected when applications supplied untrusted code with an unsupported or attacker-controlled lang, and the @astrojs/markdoc prism() extension was affected for less-trusted content authors even when Markdoc's ordinary HTML rendering was disabled. This issue is fixed in @astrojs/prism 4.1.2 and @astrojs/markdoc 2.1.2.

## Remediation

No remediation reported in collected sources

## Affected products and versions

- withastro / astro: < 7.4.3 (affected). Source: CNA: GitHub_M
- @astrojs / prism: < 4.1.2 (affected). Source: CNA: GitHub_M
- @astrojs / markdoc: >= 0.3.0, < 2.1.2 (affected). Source: CNA: GitHub_M

## Severity and prioritization

- CVSS 3.1: 5.4 (medium); CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N; source: CNA: GitHub_M

- CISA KEV: No listing in collected sources

- EPSS: Not available

- SSVC: Not available

- Weaknesses: CWE-79

## Exploit evidence

No exploit evidence in collected sources. This is not proof of no exploitation.

## References

- https://github.com/withastro/astro/security/advisories/GHSA-ff38-p3qj-4pmf (CNA: GitHub_M; x_refsource_CONFIRM)

- https://github.com/withastro/astro/commit/edfbf4ab34ff007ae8f7188af76a023a15c9443d (CNA: GitHub_M; x_refsource_MISC)

- https://github.com/withastro/astro/releases/tag/@astrojs/markdoc@2.1.2 (CNA: GitHub_M; x_refsource_MISC)

- https://github.com/withastro/astro/releases/tag/@astrojs/prism@4.1.2 (CNA: GitHub_M; x_refsource_MISC)

## Provenance

- CNA: GitHub_M: https://www.cve.org/CVERecord?id=CVE-2026-126365; retrieved 2026-11-12; source updated 2026-11-12

Revision: 604e1a89ec6c3f2d5a119c09310eb3da679f461199a1cd6506fb804f5a3ce495

Canonical: https://y2.dev/cve/CVE-2026-126365

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