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Authentication mechanism absence or evasion

Need​

Implementation of a robust and secure authentication mechanism

Context​

  • Usage of Dart for building cross-platform mobile, web, and desktop applications
  • Usage of Shelf for managing and organizing data in Node.js applications
  • Usage of shelf_io for managing I/O operations with Shelf

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().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}"');
}

In the above code, we are using the Shelf framework in Dart to create a simple backend server. The server listens on port 8080 and returns a response containing the requested URL for every request it receives.

The vulnerability here lies in the absence of an authentication mechanism. Any request that the server receives is processed without checking if the client is authenticated. This means that an attacker can send a request to the server and receive a response without having an active session.

In a real-world application, this could lead to unauthorized access to protected resources. For example, if this server was used to handle requests for user data, an attacker could potentially access this data without needing to provide any form of identification.

To fix this vulnerability, we need to implement an authentication mechanism. This could be done using middleware in the Shelf pipeline that checks for an authentication token in the request headers. If the token is not present or is invalid, the server should return an unauthorized response.

Steps​

  • Introduce an authentication middleware in the pipeline to handle authentication.
  • The middleware should verify the identity of the user before processing the request further.
  • Use secure methods for storing and verifying user credentials. Avoid storing passwords in plain text.
  • Implement session management. Once a user is authenticated, they should be given a session that expires after a certain period of inactivity.
  • Ensure that the session token is securely transmitted and stored on the client side. It should not be accessible to JavaScript running in the browser (to prevent XSS attacks) and should only be sent over secure connections (to prevent MITM attacks).
  • Implement rate limiting to prevent brute force attacks.
  • Provide a logout mechanism that invalidates the session on the server side.

Compliant code​

import 'dart:convert';
import 'package:shelf/shelf.dart' as shelf;
import 'package:shelf/shelf_io.dart' as io;
import 'package:shelf_auth/shelf_auth.dart';
import 'package:shelf_session/shelf_session.dart';
import 'package:shelf_session_memory/shelf_session_memory.dart';

void main() {
  var sessionMiddleware = SessionMiddleware(
    SessionMemoryStore(),
    cookieName: 'session',
    sessionSerializer: const SimpleSessionSerializer(),
  );

  var authMiddleware = authenticate(
    [new BasicAuthenticator(_verifyUser)],
    session: sessionMiddleware.createSessionHandler(),
    allowHttp: false,
  );

  var handler = const shelf.Pipeline()
      .addMiddleware(sessionMiddleware)
      .addMiddleware(authMiddleware)
      .addHandler(_echoRequest);

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

Future<bool> _verifyUser(String username, String password) async {
  // Replace this with your own logic
  return username == 'admin' && password == 'password';
}

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

The updated code introduces an authentication middleware and a session middleware to the pipeline.

The sessionMiddleware is responsible for managing user sessions. It uses an in-memory store to keep track of active sessions. The session data is stored in a cookie named 'session'. The SimpleSessionSerializer is used to serialize and deserialize the session data.

The authMiddleware is responsible for authenticating users. It uses the Basic Authentication scheme. The _verifyUser function is used to verify the username and password. In this example, it simply checks if the username is 'admin' and the password is 'password'. In a real application, you should replace this with your own logic, such as checking the credentials against a database. The allowHttp option is set to false to ensure that the authentication data is only sent over secure connections.

The sessionMiddleware and authMiddleware are added to the pipeline before the request handler. This ensures that every request goes through the session management and authentication process before it is processed further.

The _echoRequest function is the request handler. It simply returns a response with the requested URL.

This code provides a basic level of authentication and session management. However, it does not implement all the security measures mentioned in the previous steps. For example, it does not implement rate limiting or a logout mechanism. You should add these features according to the needs of your application.

References​

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