@nestjs/platform-fastify: Path-scoped middleware bypass via absolute-form request targets

Summary

On the Fastify adapter, an HTTP request that uses an absolute-form request target (GET http://host/path HTTP/1.1 instead of GET /path HTTP/1.1) reaches the route handler without running the path-scoped Nest middleware bound to that route. Applications that enforce authentication or authorization in middleware execute the protected handler with those checks skipped.

Impact

Any application that

• uses @nestjs/platform-fastify, and
• binds middleware to specific paths via MiddlewareConsumer.forRoutes(...) or .exclude(...), and
• is reachable by a client that controls the raw request line.

Node's HTTP server accepts absolute-form targets, so no special server configuration is needed. Exposure is reduced when a reverse proxy in front of the application rewrites the request target to origin-form, which most do.

Where the bypassed middleware performs authentication or authorization, the result is an authentication or authorization bypass. Where it performs logging, rate limiting or body handling, those are silently skipped instead.

Details

Fastify's router (find-my-way) resolves an absolute-form target to its path before matching, so the route handler is dispatched normally. Two places on the middleware side matched against the raw request target instead:

1. The bundled copy of the @fastify/middie engine at packages/platform-fastify/adapters/middie/fastify-middie.ts. NestJS carried this fork to apply an earlier path-decoding fix and it did not track the upstream absolute-form fix released in @fastify/middie@9.3.4.
2. FastifyAdapter's own re-check in createMiddlewareFactory(), which tests the middleware path regexp against req.originalUrl.

Both normalized and percent-decoded the target, but neither resolved absolute-form to a path, so the router and the middleware layer disagreed about which path was being requested.

A second, related defect contributed. Because the adapter always passes routerOptions (to install the version constraint), Fastify did not reflect the deprecated top-level router options (ignoreTrailingSlash, ignoreDuplicateSlashes, caseSensitive, useSemicolonDelimiter) in initialConfig.routerOptions, which is what the middleware engine reads. Applications passing those options at the top level had middleware normalize paths differently from the router, which widened the mismatch.

Proof of concept

@Controller('users')
export class UsersController {
  @Get()
  findAll() {
    return 'protected data';
  }
}

@Module({ controllers: [UsersController] })
export class AppModule implements NestModule {
  configure(consumer: MiddlewareConsumer) {
    consumer
      .apply((req, res) => res.end('blocked by auth middleware'))
      .forRoutes({ path: 'users', method: RequestMethod.GET });
  }
}

supertest and light-my-request always emit origin-form targets, so the request has to be written to the socket:

const { connect } = require('node:net');

const socket = connect(3000, '127.0.0.1', () => {
  socket.write(
    'GET http://127.0.0.1:3000/users HTTP/1.1\r\n' +
      'Host: 127.0.0.1:3000\r\n' +
      'Connection: close\r\n\r\n',
  );
});
socket.pipe(process.stdout);

Observed on an affected version: protected data — the middleware did not run. Expected, and observed on a patched version: blocked by auth middleware.

Patches

Fixed in 12.0.2 and 11.2.4. Upgrading to 12.0.3 or 11.2.5 is recommended.

• The bundled @fastify/middie fork was removed and the package now depends on @fastify/middie@9.3.4, which resolves absolute-form targets before matching.
• The adapter resolves absolute-form targets in its own route check, mirroring find-my-way.
• Deprecated top-level Fastify router options are folded into routerOptions so the middleware engine and the router normalize paths identically.

Workarounds

If you cannot upgrade, reject non-origin-form request targets before middleware runs. Register the hook on the Fastify instance before the application is initialized, so that it runs ahead of the middleware engine's own onRequest hook, and confirm with the request above that the rejection takes effect:

const adapter = new FastifyAdapter();
adapter.getInstance().addHook('onRequest', (request, reply, done) => {
  const target = request.raw.url ?? '';
  // "*" is the legitimate request target of "OPTIONS * HTTP/1.1"
  if (target[0] !== '/' && target !== '*') {
    reply.code(400).send();
    return;
  }
  done();
});

Rejecting or normalizing absolute-form targets at a reverse proxy in front of the application is equally effective.

Credit

Reported by ZeroVuln Labs.