How to fix CVE-2025-29927 – Step-by-Step Guide
CVE-2025-29927, a critical Next.js Middleware Authorization Bypass (CVSS 9.1), was published on March 21, 2025. This vulnerability impacts Next.js applications, allowing unauthorized access to protected routes by bypassing security middleware.
What is Next.js Middleware Authorization Bypass?
This critical vulnerability in Next.js middleware stems from improper handling of the `x-middleware-subrequest` header. Attackers can manipulate this header to bypass authorization checks implemented within middleware. This allows them to gain unauthorized access to routes that should be protected by your application's access control logic.
Impact and Risks for your Infrastructure
The primary impact is a severe authentication and authorization bypass in Next.js applications. Attackers can access sensitive pages, API routes, and data without valid credentials. This can lead to data breaches, unauthorized actions, and compromise of user privacy and system integrity.
Step-by-Step Mitigation Guide
To mitigate CVE-2025-29927, immediately upgrade your Next.js application to fixed versions: 15.2.3+, 14.2.25+, 13.5.9+, or 12.3.5+. Verify the update by checking your `package.json` and running `npm list next` or `yarn list next`. Ensure your deployment pipeline reflects the updated dependency.
- 1Upgrade Next.js immediately to 15.2.3+, 14.2.25+, 13.5.9+, or 12.3.5+.
- 2Block x-middleware-subrequest header at CDN/reverse proxy level.
- 3Move critical authorization checks from middleware into route handlers/server components.
- 4Audit all middleware.ts files for security-critical authorization logic.
- 5Deploy Cloudflare WAF rule or equivalent to block the header manipulation.
- 6Rotate session tokens and audit access logs for potential exploitation.