How to fix CVE-2025-29927 – Step-by-Step Guide
CVE-2025-29927, a critical Next.js Middleware Authorization Bypass (CVSS 9.1), has been identified. This vulnerability allows attackers to circumvent access controls in Next.js applications.
What is Next.js Middleware Authorization Bypass?
This vulnerability affects Next.js applications utilizing middleware for access control. Attackers can craft requests by manipulating the `x-middleware-subrequest` header. This bypasses intended authorization checks, granting unauthorized access to protected routes and resources.
Impact and Risks for your Infrastructure
The primary impact is an authentication and authorization bypass. Attackers can gain unauthorized access to sensitive pages, API routes, and data. This could lead to data breaches, unauthorized actions, and compromise of application integrity.
Step-by-Step Mitigation Guide
To fix, upgrade Next.js 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 middleware authorization logic now functions as expected.
- 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.