How to fix CVE-2025-29927 – Step-by-Step Guide
CVE-2025-29927, a critical Next.js Middleware Authorization Bypass (CVSS 9.1), has been identified. This vulnerability allows unauthorized access to protected routes in Next.js applications. Immediate action is required to secure your deployments.
What is Next.js Middleware Authorization Bypass?
This vulnerability in Next.js middleware stems from improper handling of the x-middleware-subrequest header. Attackers can craft requests that manipulate this header, tricking the middleware into bypassing intended authorization logic. This allows them to gain unauthorized access to routes that should be protected by your application's access control mechanisms.
Impact and Risks for your Infrastructure
The primary impact is a severe authentication and authorization bypass, allowing unauthorized access to sensitive data and functionality. Attackers can access protected pages and API routes, potentially leading to data breaches, unauthorized operations, or full compromise of application integrity. This directly impacts business operations and user trust.
Step-by-Step Mitigation Guide
To mitigate CVE-2025-29927, update your Next.js installation to version 15.2.3+, 14.2.25+, 13.5.9+, or 12.3.5+. Verify the fix by checking your package.json and package-lock.json files for the updated Next.js version, then redeploy your application. Ensure no unauthorized access occurs to previously protected routes.
- 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.