December 06, 9:05 PM PST: If your application was online and unpatched as of December 4th, 2025 at 1:00 PM PT, we strongly encourage you to rotate any secrets it uses, starting with your most critical ones.

December 06, 7:29 AM PST: An npm package has been released to update affected Next.js apps. Use npx fix-react2shell-next to update now, or visit the GitHub repository to learn more.

A critical vulnerability has been identified in the React Server Components (RSC) protocol. The issue is rated CVSS 10.0 and can allow remote code execution when processing attacker-controlled requests in unpatched environments.

This vulnerability originates in the upstream React implementation (CVE-2025-55182). This advisory (CVE-2025-66478) tracks the downstream impact on Next.js applications using the App Router.

Impact

The vulnerable RSC protocol allowed untrusted inputs to influence server-side execution behavior. Under specific conditions, an attacker could craft requests that trigger unintended server execution paths. This can result in remote code execution in unpatched environments.

All users should upgrade to a patched version immediately. See the required action section for specific instructions.

Affected Next.js Versions

Applications using React Server Components with the App Router are affected when running:

• Next.js 15.x
• Next.js 16.x
• Next.js 14.3.0-canary.77 and later canary releases

Next.js 13.x, Next.js 14.x stable, Pages Router applications, and the Edge Runtime are not affected.

Fixed Versions

The vulnerability is fully resolved in the following patched Next.js releases:

• 15.0.5
• 15.1.9
• 15.2.6
• 15.3.6
• 15.4.8
• 15.5.7
• 16.0.7

We also released patched canary releases for Next.js 15 and 16:

• 15.6.0-canary.58 (for 15.x canary releases)
• 16.1.0-canary.12 (for 16.x canary releases)

These versions include the hardened React Server Components implementation.

Required Action

All users should upgrade to the latest patched version in their release line:

If you are on Next.js 14.3.0-canary.77 or a later canary release, downgrade to the latest stable 14.x release:

If you're currently using canary releases to enable PPR, you can update to 15.6.0-canary.58, which includes a fix for the vulnerability while continuing to support PPR. For other ways to patch older versions, see this discussion post.

Run npx fix-react2shell-next to launch an interactive tool which can check versions and perform deterministic version bumps per the recommended versions above. See the GitHub repository for full details.

There is no workaround—upgrading to a patched version is required.

Rotating environment variables

Once you have patched your version and re-deployed your application, we recommend rotating all your application secrets. Learn about working with environment variables in the documentation here.

Resources

• Security advisories: React (CVE-2025-55182), Next.js (CVE-2025-66478)
• React blog: Critical Security Vulnerability in React Server Components
• Vercel Knowledge Base: React2Shell Security Bulletin
• Netlify Blog: Netlify's response to the critical React security vulnerability
• AWS Security Blog: China-nexus cyber threat groups rapidly exploit React2Shell vulnerability
• Google Cloud Blog: Responding to CVE-2025-55182: Secure your React and Next.js workloads
• Fastly Blog: Fastly's Proactive Protection for React2Shell, Critical React RCE CVE-2025-55182 and CVE-2025-66478
• Akamai Blog: CVE-2025-55182: React and Next.js Server Functions Deserialization RCE

Discovery

Thank you to Lachlan Davidson for discovering and responsibly disclosing this vulnerability. We are intentionally limiting technical detail in this advisory to protect developers who have not yet upgraded.