How to fix CVE-2025-29927 – Step-by-Step Guide
CVE-2025-29927, a critical Next.js Middleware Authorization Bypass, 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 critical vulnerability, CVE-2025-29927, specifically targets Next.js applications utilizing middleware for access control. Attackers can exploit a flaw in how Next.js processes the x-middleware-subrequest header. By manipulating this header, unauthorized users can bypass intended authorization checks and gain access to restricted routes.
Impact and Risks for your Infrastructure
The primary impact is a severe authentication and authorization bypass. Attackers can access sensitive data, protected pages, and API routes without valid credentials. This compromises data integrity, user privacy, and could lead to significant business disruption.
Step-by-Step Mitigation Guide
To mitigate CVE-2025-29927, update your Next.js application to version 15.2.3+, 14.2.25+, 13.5.9+, or 12.3.5+. Verify the fix by ensuring your package.json reflects the updated version and running `npm install` or `yarn install`. Confirm no unauthorized access is possible to 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.