Affected: CleanStart: jitsucom-jitsu

Security vulnerability affects the jitsucom-jitsu package. This issue is resolved in later releases. See references for vulnerability details.

PostCSS takes a CSS file and provides an API to analyze and modify its rules by transforming the rules into an Abstract Syntax Tree. Versions prior to 8.5.10 do 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. Version 8.5.10 fixes the issue.

Affected: npm: postcss

# 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

```javascript 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 = `<style>${output}</style>`;

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

## Credits Discovered and reported by [Sunil Kumar](https://tharvid.in) ([@TharVid](https://github.com/TharVid))

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Affected: Ubuntu:20.04:LTS: node-postcss, Ubuntu:22.04:LTS: node-postcss, Ubuntu:24.04:LTS: node-postcss, Ubuntu:25.10: node-postcss, Ubuntu:26.04:LTS: node-postcss

PostCSS takes a CSS file and provides an API to analyze and modify its rules by transforming the rules into an Abstract Syntax Tree. Versions prior to 8.5.10 do 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. Version 8.5.10 fixes the issue.

Ein entfernter, anonymer Angreifer kann mehrere Schwachstellen in IBM App Connect Enterprise ausnutzen, um beliebigen Programmcode auszuführen, Daten zu manipulieren, Cross-Site-Scripting-Angriffe durchzuführen, vertrauliche Informationen offenzulegen oder einen Denial-of-Service-Zustand auszulösen.