MIGRATION: middleware.ts to proxy.ts

MIGRATION: middleware.ts to proxy.ts

Overview

Next.js 16 renames middleware.ts to proxy.ts and the middleware export to proxy. This is a breaking change with security implications (CVE-2025-29927).

Why This Change Matters

CVE-2025-29927: Middleware-based authentication is fundamentally broken in Next.js. Middleware cannot reliably protect routes because:

• Middleware runs at the edge, but authentication state lives in databases/​sessions
• Race conditions between middleware checks and route handlers
• Middleware can be bypassed through direct route access
• Edge runtime limitations prevent proper session verification

The rename to "proxy" clarifies that this API is for request/​response manipulation, not security.

Migration Steps

1. Rename the File

# Old location
src/​middleware.ts

# New location
src/​proxy.ts

2. Rename the Export

Before (Next.js 15):

export function middleware(request: NextRequest) {
  return NextResponse.next();
}

export const config = {
  matcher: ['/​api/:path*', '/​dashboard/:path*'],
};

After (Next.js 16):

export function proxy(request: NextRequest) {
  return NextResponse.next();
}

export const config = {
  matcher: ['/​api/:path*', '/​dashboard/:path*'],
};

3. Update Configuration

If using next.config.js or next.config.ts:

const nextConfig = {
  experimental: {
  },
};

No configuration changes needed for proxy. The framework detects proxy.ts automatically.

Security Migration

If you were using middleware for authentication, you must migrate to route-level protection.

Before (Insecure)

export function middleware(request: NextRequest) {
  const token = request.cookies.get('auth-token');

  if (!token) {
    return NextResponse.redirect(new URL('/​login', request.url));
  }

  return NextResponse.next();
}

export const config = {
  matcher: ['/​dashboard/:path*'],
};

After (Secure)

proxy.ts:

export function proxy(request: NextRequest) {
  const response = NextResponse.next();

  response.headers.set('x-custom-header', 'value');

  return response;
}

app/​dashboard/​layout.tsx:

import { redirect } from 'next/​navigation';
import { verifySession } from '@/​lib/​auth';

export default async function DashboardLayout({
  children,
}: {
  children: React.ReactNode;
}) {
  const session = await verifySession();

  if (!session) {
    redirect('/​login');
  }

  return <>{children}</>;
}

Key differences:

• Authentication logic moves to Server Components
• Session verification happens in the same runtime as data access
• No race conditions between auth check and data fetch
• Can access database/​session store reliably

Valid Use Cases for proxy.ts

Use proxy.ts for:

1. Request/​response header manipulation

   export function proxy(request: NextRequest) {
     const response = NextResponse.next();
     response.headers.set('x-frame-options', 'DENY');
     return response;
   }
   

2. Request logging/​monitoring

   export function proxy(request: NextRequest) {
     console.log(`${request.method} ${request.url}`);
     return NextResponse.next();
   }
   

3. URL rewriting

   export function proxy(request: NextRequest) {
     if (request.nextUrl.pathname === '/​old-path') {
       return NextResponse.rewrite(new URL('/​new-path', request.url));
     }
     return NextResponse.next();
   }
   

4. Geolocation routing

   export function proxy(request: NextRequest) {
     const country = request.geo?.country;
     if (country === 'US') {
       return NextResponse.rewrite(new URL('/​us', request.url));
     }
     return NextResponse.next();
   }
   

Do NOT Use proxy.ts For

• Authentication/​authorization checks
• Session validation
• Database queries
• Complex business logic
• Rate limiting (use route handlers instead)

Migration Checklist

• Rename middleware.ts to proxy.ts
• Rename middleware export to proxy
• Remove authentication logic from proxy
• Move authentication to Server Components/​Route Handlers
• Test that routes are properly protected
• Verify edge cases (direct route access, API routes, etc.)
• Update tests that reference middleware

Common Errors

Error: "middleware is not exported"

You forgot to rename the export from middleware to proxy.

Error: "proxy is not a function"

Ensure you're exporting a function named proxy, not a default export.

Error: "Cannot access database in proxy"

Proxy runs at the edge runtime. Move database access to route handlers or Server Components.

Additional Resources

• CVE-2025-29927: Next.js Middleware Authentication Vulnerability
• Next.js 16 Migration Guide: Proxy API
• Next.js Security Best Practices: Route-Level Protection