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Security Advisory: CVE-2025-66478
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Wednesday, December 3rd 2025

Security Advisory: CVE-2025-66478

Posted by
Josh Story
Josh Story@joshcstory
Sebastian Markbåge
Sebastian Markbåge@sebmarkbage

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.

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:

Terminal
npm install next@15.0.5   # for 15.0.x
npm install next@15.1.9   # for 15.1.x
npm install next@15.2.6   # for 15.2.x
npm install next@15.3.6   # for 15.3.x
npm install next@15.4.8   # for 15.4.x
npm install next@15.5.7   # for 15.5.x
npm install next@16.0.7   # for 16.0.x
 
npm install next@15.6.0-canary.58   # for 15.x canary releases
npm install next@16.1.0-canary.12   # 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:

Terminal
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.

Terminal
npx fix-react2shell-next

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

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.

References