Need

Secure service configuration - Proper host verification

Context

• Usage of Dart for building cross-platform mobile, web, and desktop applications
• Usage of Shelf for managing and organizing data in a Node.js application
• Usage of shelf_io for managing input/output operations in a Shelf application

Description

Non compliant code

        import 'package:shelf/shelf.dart' as shelf;
import 'package:shelf/shelf_io.dart' as io;

void main() {
  var handler = const shelf.Pipeline().addMiddleware(shelf.logRequests())
      .addHandler(_echoRequest);

  io.serve(handler, '0.0.0.0', 8080).then((server) {
    print('Serving at http://${server.address.host}:${server.port}');
  });
}

shelf.Response _echoRequest(shelf.Request request) {
  return shelf.Response.ok('Request for "${request.url}"');
}
        
        

In the above code, the server is set up to listen for incoming connections on all network interfaces (0.0.0.0) and on port 8080. This is done using the io.serve(handler, '0.0.0.0', 8080) line.

The problem with this configuration is that it does not restrict incoming connections from unknown external hosts. This means that any device, regardless of its location or network, can send a request to this server as long as it knows the server's IP address and port number.

The server is also set to respond to all requests with an OK response and the requested URL, regardless of the source of the request. This is done in the _echoRequest function.

This configuration is insecure because it exposes the server to potential attacks from unknown external hosts. An attacker could potentially use this open connection to send malicious requests to the server, or to gain unauthorized access to the server and its data.

To fix this vulnerability, the server should be configured to only accept connections from known and trusted hosts. This can be done by implementing a host verification mechanism that checks the source of each incoming request before processing it.

Steps

• Restrict the IP addresses that can connect to your service. Instead of '0.0.0.0', which allows all IP addresses, specify the IP addresses that you trust.
• Implement an authentication mechanism to verify the identity of the incoming connections. This could be a username/password, API key, or a certificate.
• Use a firewall or a similar security measure to block unwanted traffic.
• Regularly update and patch your system and libraries to protect against known vulnerabilities.
• Monitor your system for suspicious activity. This could be done through logging and analyzing the logs for patterns that indicate an attack.

Compliant code

        import 'package:shelf/shelf.dart' as shelf;
import 'package:shelf/shelf_io.dart' as io;

void main() {
  var handler = const shelf.Pipeline().addMiddleware(shelf.logRequests())
      .addHandler(_echoRequest);

  io.serve(handler, 'localhost', 8080).then((server) {
    print('Serving at http://${server.address.host}:${server.port}');
  });
}

shelf.Response _echoRequest(shelf.Request request) {
  return shelf.Response.ok('Request for "${request.url}"');
}
        
        

The original code was vulnerable because it was configured to accept connections from any IP address. This is a security risk because it allows any external host to connect to the service, potentially leading to unauthorized access or attacks.

The fixed code restricts the service to only accept connections from 'localhost' (127.0.0.1), which is the IP address of the local machine. This means that only processes running on the same machine can connect to the service. This is a common configuration for services that are not intended to be accessible from the internet.

Please note that this fix might not be suitable for all use cases. If your service needs to be accessible from other machines, you should implement additional security measures. These could include:

- An authentication mechanism to verify the identity of the incoming connections. This could be a username/password, API key, or a certificate.
- A firewall or a similar security measure to block unwanted traffic.
- Regular updates and patches to your system and libraries to protect against known vulnerabilities.
- Monitoring your system for suspicious activity. This could be done through logging and analyzing the logs for patterns that indicate an attack.

References

• 060. Insecure service configuration - Host verification