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. This flaw allows unauthorized access to protected routes, posing a significant security risk.
What is Next.js Middleware Authorization Bypass?
This critical vulnerability in Next.js middleware enables attackers to bypass authorization checks. By manipulating the `x-middleware-subrequest` header, malicious actors can trick the application into granting unauthorized access. This circumvents intended access controls, compromising route protection.
Impact and Risks for your Infrastructure
The primary impact is an authentication and authorization bypass, allowing unauthorized access to sensitive data and functionality. Attackers can access protected pages and API routes without valid credentials, leading to data breaches, unauthorized actions, or system compromise.
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 `package.json` reflects the updated version and running `npm install` or `yarn install` to apply the patch. Conduct thorough testing of authorization flows.
- 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.