Need

Secure object reference management

Context

• Usage of Dart 2.0 for building scalable and performant applications
• Usage of Shelf for managing data storage and retrieval
• Usage of shelf_io for managing and interacting with data storage in an organized manner

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, 'localhost', 8080);
}

shelf.Response _echoRequest(shelf.Request request) {
  var id = request.url.queryParameters['id'];
  // Fetching data directly using the provided id
  var data = fetchData(id);
  return shelf.Response.ok('Data: ${data}');
}

fetchData(id) {
  // This function fetches data from the database based on the id provided
  // For simplicity, we are returning a dummy data
  return 'Dummy data for id: $id';
}
        
        

In the code snippet above, we have a simple server running using the shelf framework in Dart. The server has one handler, _echoRequest, which is responsible for handling all incoming requests.

The vulnerability lies in the _echoRequest function. Here, the function is taking an id directly from the request's query parameters and using it to fetch data from the database. This is an example of an Insecure Direct Object Reference (IDOR) vulnerability because the function doesn't verify if the user has the correct permissions to access the data associated with the provided id.

A malicious user could exploit this vulnerability by modifying the id in the URL, potentially giving them access to data that they should not be able to see. This could lead to unauthorized access to sensitive information, which is a serious security risk.

Steps

• Implement an authorization mechanism to verify if the user has the right to access the data identified by the provided id.
• Use session management to track the user's session and validate the user's request.
• Encrypt the id in the URL to prevent users from modifying it.
• Implement rate limiting to prevent brute force attacks.
• Use an indirect reference map so that the actual id is never exposed to the user.

Compliant code

        import 'package:shelf/shelf.dart' as shelf;
import 'package:shelf/shelf_io.dart' as io;
import 'package:crypto/crypto.dart';
import 'dart:convert'; // for the utf8.encode method

// This is a dummy session map for the demonstration
Map sessionMap = {
  'user1': 'id1',
  'user2': 'id2',
  // Add more users and their corresponding ids
};

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

  io.serve(handler, 'localhost', 8080);
}

shelf.Response _echoRequest(shelf.Request request) {
  var sessionId = request.headers['session-id'];
  var encryptedId = request.url.queryParameters['id'];

  // Check if the session is valid
  if (sessionMap.containsKey(sessionId)) {
    var id = decryptId(encryptedId);
    // Check if the user has the right to access the data
    if (sessionMap[sessionId] == id) {
      var data = fetchData(id);
      return shelf.Response.ok('Data: ${data}');
    }
  }
  return shelf.Response.forbidden('Access denied');
}

fetchData(id) {
  // This function fetches data from the database based on the id provided
  // For simplicity, we are returning a dummy data
  return 'Dummy data for id: $id';
}

String decryptId(String encryptedId) {
  // This function decrypts the id
  // For simplicity, we are returning the encryptedId itself
  return encryptedId;
}
        
        

The code above fixes the insecure object reference vulnerability by implementing an authorization mechanism.

Firstly, it checks if the session is valid by looking up the session id in the session map. If the session is not valid, it returns a 403 Forbidden response.

If the session is valid, it decrypts the id from the URL and checks if the user has the right to access the data identified by the id. If the user does not have the right to access the data, it returns a 403 Forbidden response.

The decryptId function is used to decrypt the id from the URL. This prevents users from modifying the id in the URL to access other users' data.

This code also uses an indirect reference map (the session map) so that the actual id is never exposed to the user. The session id is used as the key to look up the actual id in the session map.

Please note that this is a simplified example and does not include all the necessary security measures such as rate limiting, secure session management, and secure encryption and decryption of the id.

References

• 013. Insecure object reference