Insecure or unset HTTP headers - Accept - Dart

Need

Enforce secure and properly set HTTP headers for the Accept field

Context

1. Usage of Dart 2.0 for efficient and modern web and mobile app development
2. Usage of Shelf for ORM (Object-Relational Mapping) in Node.js

Description

Insecure Code Example

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

shelf.Response handleRequest(shelf.Request request) {
  // The application does not set the Accept header
  return shelf.Response.ok('Hello, World!');
}

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

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

In the above Dart code, we have a simple server that uses the Shelf framework. The `handleRequest` function is used to handle incoming requests and respond with 'Hello, World!'. The vulnerability lies in the fact that the server does not set the `Accept` HTTP header for the response. This means that the server does not specify what media types are acceptable for the response, which can lead to a potential security risk. An attacker could exploit this vulnerability by sending a request with a MIME type that the server does not expect or cannot handle correctly. This could lead to unexpected behaviors in the application and potentially cause security issues. For instance, an attacker could send a request with a malicious `Content-Type` in the header. Since the server does not specify the `Accept` header, it might interpret the malicious content and cause harm to the application or its data. In conclusion, not setting the `Accept` header or allowing any MIME type in the requests can expose the application to potential attacks and should be avoided.

Steps

1. Identify the acceptable MIME types for your application.
2. Modify the handleRequest function to set the Accept header with the acceptable MIME types.
3. Ensure that the application rejects requests with unacceptable MIME types.

Secure Code Example

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

shelf.Response handleRequest(shelf.Request request) {
  // Check if the request's Accept header is set to an acceptable MIME type
  if (request.headers['Accept'] != 'application/json') {
    // If not, return a 406 Not Acceptable response
    return shelf.Response(406, body: 'Not Acceptable');
  }

  // If the Accept header is set to an acceptable MIME type, process the request as usual
  return shelf.Response.ok('Hello, World!', headers: {'Content-Type': 'application/json'});
}

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

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

The updated code now checks if the request's `Accept` header is set to an acceptable MIME type (`application/json` in this case). If the `Accept` header is not set to an acceptable MIME type, the application returns a `406 Not Acceptable` response. This prevents an attacker from causing unexpected behaviors by sending requests with incorrect content-types. The `handleRequest` function has been modified to include a check for the `Accept` header in the incoming request. If the `Accept` header is not set to `application/json`, the function returns a `406 Not Acceptable` response. This ensures that the application only processes requests with acceptable MIME types. The `handleRequest` function also sets the `Content-Type` header in the response to `application/json`. This informs the client about the format of the response body. By checking the `Accept` header in the request and setting the `Content-Type` header in the response, the application can prevent unexpected behaviors caused by incorrect content-types. This makes the application more secure against potential attacks.

References

Last updated

2023/09/18