🚨 [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 upgrade. 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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[coderabbitai]

Walkthrough

This change updates the postcss development dependency from version 8.5.6 to 8.5.10 in the package.json file. The update represents a patch-level version increase within the same minor version series. No other dependencies, configuration settings, or scripts are modified in this change.

🚥 Pre-merge checks | ✅ 4

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly identifies the main change: upgrading postcss from 8.5.6 to 8.5.10 and indicates it addresses security vulnerabilities.
Description check	✅ Passed	The description is directly related to the changeset, providing detailed security context, advisory information, and release notes for the postcss upgrade.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

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[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against the current code and only fix it if needed.

Inline comments:
In `@package.json`:
- Around line 50-54: The lockfile contains mixed postcss versions causing CI to
install 8.5.6; regenerate the pnpm lockfile so postcss is consistently 8.5.10
and postcss-import resolves to the same version. Run the appropriate lock
regeneration (e.g., remove/refresh pnpm-lock.yaml and run pnpm install) ensuring
package.json's devDependencies entries for "postcss" and "postcss-import"
resolve to postcss@8.5.10, then commit the updated pnpm-lock.yaml so CI uses the
updated dependency tree.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Repository UI

Review profile: CHILL

Plan: Pro

Run ID: 0f5e2615-d5a0-43ed-aa18-9858a6cf577d

📥 Commits

Reviewing files that changed from the base of the PR and between db27049 and da86009.

⛔ Files ignored due to path filters (1)

• pnpm-lock.yaml is excluded by !**/pnpm-lock.yaml

📒 Files selected for processing (1)

• package.json

[coderabbitai]

⚠️ Potential issue | 🟠 Major

🧩 Analysis chain

🏁 Script executed:

#!/bin/bash
set -euo pipefail

if [ -f pnpm-lock.yaml ]; then
  echo "Found pnpm-lock.yaml"
  echo "Checking for postcss resolved version 8.5.10..."
  # Look for the actual resolved package entry
  rg -n "postcss@8\.5\.10" pnpm-lock.yaml || {
    echo "ERROR: Could not find postcss@8.5.10 in pnpm-lock.yaml"
    exit 1
  }

  # Also ensure there's no lingering postcss@8.5.6
  rg -n "postcss@8\.5\.6" pnpm-lock.yaml && {
    echo "ERROR: Found postcss@8.5.6 in pnpm-lock.yaml"
    exit 1
  } || true
else
  echo "ERROR: pnpm-lock.yaml not found; cannot verify resolution."
  exit 1
fi

Repository: tailwindlabs/tailwindcss

Length of output: 1321

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Lockfile must be regenerated to fully update postcss to 8.5.10.

The pnpm-lock.yaml contains both postcss@8.5.10 and lingering entries of postcss@8.5.6 (including postcss-import@16.1.1(postcss@8.5.6)). CI will install the old 8.5.6 version unless the lockfile is regenerated.

🤖 Prompt for AI Agents

Verify each finding against the current code and only fix it if needed.

In `@package.json` around lines 50 - 54, The lockfile contains mixed postcss
versions causing CI to install 8.5.6; regenerate the pnpm lockfile so postcss is
consistently 8.5.10 and postcss-import resolves to the same version. Run the
appropriate lock regeneration (e.g., remove/refresh pnpm-lock.yaml and run pnpm
install) ensuring package.json's devDependencies entries for "postcss" and
"postcss-import" resolve to postcss@8.5.10, then commit the updated
pnpm-lock.yaml so CI uses the updated dependency tree.

[depfu]

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