How to fix CVE-2025-29927 – Step-by-Step Guide
CVE-2025-29927, named 'Next.js Middleware Authorization Bypass', is a critical vulnerability (CVSS 9.1) affecting Next.js applications. This flaw allows unauthorized access to protected routes, posing a significant security risk.
What is Next.js Middleware Authorization Bypass?
This vulnerability allows attackers to bypass authorization checks in Next.js middleware. By manipulating the `x-middleware-subrequest` header, malicious actors can trick the application into granting unauthorized access to routes intended to be protected by middleware-based access controls.
Impact and Risks for your Infrastructure
The primary impact is an authentication and authorization bypass in Next.js applications. Attackers can gain unauthorized access to sensitive pages, API routes, and data without valid credentials, leading to data breaches or unauthorized operations.
Step-by-Step Mitigation Guide
To fix this, update your Next.js application to a patched 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 Next.js version and redeploying your application.
- 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.