How to fix CVE-2025-29927 – Step-by-Step Guide
CVE-2025-29927 is a critical authorization bypass vulnerability affecting Next.js applications. This flaw allows unauthorized access to protected routes, posing a significant security risk. Immediate action is required to secure your deployments.
What is Next.js Middleware Authorization Bypass?
This critical vulnerability exists in Next.js middleware. Attackers can exploit it by manipulating the `x-middleware-subrequest` header. This manipulation allows them to bypass intended authorization checks, gaining unauthorized access to routes that should be protected.
Impact and Risks for your Infrastructure
The impact of CVE-2025-29927 is severe, enabling attackers to bypass authentication and authorization. This grants unauthorized access to sensitive pages and API routes, potentially leading to data breaches, unauthorized data manipulation, or complete compromise of application integrity.
Step-by-Step Mitigation Guide
To mitigate CVE-2025-29927, immediately upgrade your Next.js application to fixed versions: 15.2.3+, 14.2.25+, 13.5.9+, or 12.3.5+. After upgrading, verify the fix by testing access to previously protected routes to ensure authorization mechanisms are functioning correctly.
- 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.