How to fix CVE-2025-29927 – Step-by-Step Guide
CVE-2025-29927, named 'Next.js Middleware Authorization Bypass', is a critical vulnerability affecting Next.js applications. It allows unauthorized access to protected routes by bypassing middleware authorization checks. This fix page provides essential information and steps to secure your applications.
What is Next.js Middleware Authorization Bypass?
This critical vulnerability, CVE-2025-29927, exists in Next.js middleware. Attackers can exploit it by crafting specific requests that manipulate the 'x-middleware-subrequest' header. This manipulation tricks the middleware into bypassing intended authorization logic, allowing access to restricted resources.
Impact and Risks for your Infrastructure
The primary impact is a severe authentication and authorization bypass. Attackers can gain unauthorized access to sensitive data, protected pages, and API routes. This could lead to data breaches, privilege escalation, and compromise of the entire application's integrity.
Step-by-Step Mitigation Guide
To mitigate CVE-2025-29927, immediately upgrade your Next.js applications to versions 15.2.3+, 14.2.25+, 13.5.9+, or 12.3.5+. After upgrading, redeploy your application and thoroughly test all protected routes to ensure authorization checks are functioning correctly and the bypass is no longer possible.
- 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.