How to fix CVE-2025-29927 – Step-by-Step Guide
A critical vulnerability, CVE-2025-29927, named "Next.js Middleware Authorization Bypass," has been identified. This flaw allows unauthorized access to protected routes in Next.js applications, posing a significant security risk.
What is Next.js Middleware Authorization Bypass?
CVE-2025-29927 exploits a flaw in Next.js middleware's handling of the `x-middleware-subrequest` header. By manipulating this header, attackers can bypass intended authorization checks. This allows them to gain unauthorized access to routes that should be protected by middleware.
Impact and Risks for your Infrastructure
This critical bypass enables attackers to access sensitive data, administrative functions, or other protected resources without valid credentials. It can lead to data breaches, unauthorized actions, and compromise the integrity of your Next.js application, impacting business operations and user trust.
Step-by-Step Mitigation Guide
To mitigate CVE-2025-29927, immediately upgrade 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 application's middleware correctly enforces authorization on all protected routes after the upgrade.
- 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.