How to fix CVE-2025-29927 – Step-by-Step Guide
CVE-2025-29927 is a critical Next.js vulnerability, dubbed 'Next.js Middleware Authorization Bypass.' With a CVSS score of 9.1, it allows unauthorized access to protected routes, posing a severe risk to affected applications.
What is Next.js Middleware Authorization Bypass?
This vulnerability affects Next.js applications that rely on middleware for access control. Attackers can manipulate the `x-middleware-subrequest` header to bypass intended authorization checks. This grants them unauthorized access to routes and resources that should be protected.
Impact and Risks for your Infrastructure
The critical impact is an authentication and authorization bypass. Attackers can gain unauthorized access to sensitive pages and API routes without valid credentials. This can lead to data exposure, unauthorized actions, and compromise of application integrity.
Step-by-Step Mitigation Guide
To remediate CVE-2025-29927, update Next.js to version 15.2.3+, 14.2.25+, 13.5.9+, or 12.3.5+. Verify the update in your `package.json` and `package-lock.json`, then rebuild and redeploy your application to ensure the fix is active.
- 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.