How to fix CVE-2025-29927 – Step-by-Step Guide
CVE-2025-29927, named 'Next.js Middleware Authorization Bypass', is a critical vulnerability (CVSS 9.1) affecting Next.js applications. It allows unauthorized access to protected routes and API endpoints. This bypass undermines security controls, posing a significant 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, allowing entry to otherwise restricted areas of the application.
Impact and Risks for your Infrastructure
The primary impact is an authentication and authorization bypass in Next.js applications. Attackers can gain unauthorized access to protected pages and API routes, potentially leading to data exposure, privilege escalation, or full system compromise. This directly compromises the integrity and confidentiality of sensitive application data.
Step-by-Step Mitigation Guide
To fix CVE-2025-29927, immediately update your Next.js application to a patched version: 15.2.3+, 14.2.25+, 13.5.9+, or 12.3.5+. Verify the update by checking your package.json and yarn.lock/package-lock.json files, then redeploy your application. Ensure all Next.js instances are running a fixed version.
- 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.