Security Advisory: CVE-2025-66478

Sebastian Markbåge,

Josh Story

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.

Copy link to headingImpact

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.

Copy link to headingAffected 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.

Copy link to headingFixed 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.

Copy link to headingRequired Action

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

npm install [email protected]   # for 15.0.x
npm install [email protected]   # for 15.1.x
npm install [email protected]   # for 15.2.x
npm install [email protected]   # for 15.3.x
npm install [email protected]   # for 15.4.x
npm install [email protected]   # for 15.5.x
npm install [email protected]   # for 16.0.x
 
npm install [email protected]   # for 15.x canary releases
npm install [email protected]   # for 16.x canary releases

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

npm install next@14

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.

npx fix-react2shell-next

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

Copy link to headingRotating 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.

Copy link to headingResources

Copy link to headingDiscovery

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.