CVE-2026-41305: PostCSS has XSS via Unescaped </style> in its CSS Stringify Output

April 24, 2026

PostCSS v8.5.5 (latest) does not escape </style> sequences when stringifying CSS ASTs. When user-submitted CSS is parsed and re-stringified for embedding in HTML <style> tags, </style> in CSS values breaks out of the style context, enabling XSS.

References

github.com/advisories/GHSA-qx2v-qp2m-jg93
github.com/postcss/postcss
github.com/postcss/postcss/releases/tag/8.5.10
github.com/postcss/postcss/security/advisories/GHSA-qx2v-qp2m-jg93
nvd.nist.gov/vuln/detail/CVE-2026-41305

Code Behaviors & Features

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