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 flaw allows unauthorized access to protected routes by exploiting a vulnerability in Next.js middleware. Immediate action is required to secure your applications.
What is Next.js Middleware Authorization Bypass?
This vulnerability stems from improper handling of the x-middleware-subrequest header within Next.js middleware. Attackers can craft requests that manipulate this header, causing the middleware to incorrectly process authorization logic. This bypasses intended access controls, allowing unauthorized access to restricted application areas.
Impact and Risks for your Infrastructure
The primary impact is a severe authentication and authorization bypass. Attackers can gain unauthorized access to sensitive data, protected pages, and critical API routes, compromising data confidentiality and integrity. This could lead to data breaches, unauthorized operations, and reputational damage.
Step-by-Step Mitigation Guide
To mitigate CVE-2025-29927, update your Next.js applications to versions 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. Regularly review access logs for suspicious activity.
- 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.