🚨 [security] Update postcss 8.5.6 → 8.5.10 (patch)

[depfu]

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🚨 Your current dependencies have known security vulnerabilities 🚨

This dependency update fixes known security vulnerabilities. Please see the details below and assess their impact carefully. We recommend to merge and deploy this as soon as possible!

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Here is everything you need to know about this update. Please take a good look at what changed and the test results before merging this pull request.

What changed?

✳️ postcss (8.5.6 → 8.5.10) · Repo · Changelog

Security Advisories 🚨

🚨 PostCSS has XSS via Unescaped </style> in its CSS Stringify Output

PostCSS: XSS via Unescaped </style> in CSS Stringify Output

Summary

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.

Proof of Concept

const postcss = require('postcss');
// Parse user CSS and re-stringify for page embedding

const userCSS = 'body { content: "</style><script>alert(1)</script><style>"; }';

const ast = postcss.parse(userCSS);

const output = ast.toResult().css;

const html = &lt;style&gt;<span class="pl-s1"><span class="pl-kos">${</span><span class="pl-s1">output</span><span class="pl-kos">}</span></span>&lt;/style&gt;;
console.log(html);

// <style>body { content: "</style><script>alert(1)</script><style>"; }</style>

//

// Browser: </style> closes the style tag, <script> executes

Tested output (Node.js v22, postcss v8.5.5):

Input: body { content: "</style><script>alert(1)</script><style>"; }
Output: body { content: "</style><script>alert(1)</script><style>"; }
Contains </style>: true

Impact

Impact non-bundler use cases since bundlers for XSS on their own. Requires some PostCSS plugin to have malware code, which can inject XSS to website.

Suggested Fix

Escape </style in all stringified output values:

output = output.replace(/<\/(style)/gi, '<\\/$1');

Credits

Discovered and reported by Sunil Kumar (@TharVid)

Release Notes

8.5.10

• Fixed XSS via unescaped </style> in non-bundler cases (by @TharVid).

8.5.9

• Speed up source map encoding paring in case of the error.

8.5.8

• Fixed Processor#version.

8.5.7

• Improved source map annotation cleaning performance (by CodeAnt AI).

Does any of this look wrong? Please let us know.

Commits

See the full diff on Github. The new version differs by 37 commits:

• Release 8.5.10 version
• Escape </style> in CSS output (#2074)
• Update dependencies (#2073)
• Typo (#2072)
• Thread model (#2071)
• Create incident response docs (#2070)
• Release 8.5.9 version
• Avoid RegExp when we can use simple JS
• Move SECURITY.txt for docs folder to keep GitHub page cleaner
• Create SECURITY.md
• Another way to fix CI with .ts ext in tests on old Node.js
• Another way to fix CI with TS on old Node.js
• Another way to fix CI with old Node.js
• Fix another issue with Node.js 10 on CI
• Try to fix Node.js 10 on CI
• Move to oxfmt
• Update dependencies
• Add CoC from Slow Reader
• Update email
• Release 8.5.8 version
• Run git hook register
• Update Processor#version
• Release 8.5.7 version
• Fix uvu Node.js 25 support
• Update dependencies
• Speed up source map annotation cleaning by moving from RegExp
• Remove banner
• chore: speed up space-only string check in lib/parser.js (#2064)
• Update dependencies
• Add Node.js 24 and 25 to CI
• Pin CI actions
• Add new plugin
• Fix typography
• Update sponsor description
• Add Warp banner
• docs: add postcss-inline-extract plugin to plugins list (#2057)
• docs: added my if() function PostCSS plugin (#2054)

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