Insecurely generated cookies - SameSite - Dart

Need

Enforce secure generation of cookies with proper SameSite attribute configuration

Context

1. Usage of Dart for building cross-platform mobile, web, and desktop applications
2. Usage of Shelf for managing and organizing data in a Node.js application

Description

Insecure Code Example

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

shelf.Response handleRequest(shelf.Request request) {
  var response = shelf.Response.ok('Hello, World!');
  return response.change(headers: {
    'Set-Cookie': 'sessionId=123456; Secure; HttpOnly'
  });
}

The above Dart code is used to handle HTTP requests in a backend application using the Shelf framework. The `handleRequest` function creates a response with the text 'Hello, World!' and sets a cookie named `sessionId` with a value of `123456`. The cookie is marked as `Secure` and `HttpOnly`, which are good practices as they respectively ensure the cookie is only sent over HTTPS and prevent the cookie from being accessed through client-side scripts. However, the code has a significant vulnerability: it does not set the `SameSite` attribute for the cookie. The `SameSite` attribute is a security measure that browsers can use to decide whether to send cookies along with cross-site requests. If `SameSite` is not set, the browser will default to sending cookies on all requests, including cross-site ones. This can expose the application to Cross-Site Request Forgery (CSRF) attacks, where an attacker tricks a victim into performing actions on a web application in which they're authenticated. To fix this vulnerability, the `SameSite` attribute should be set to `Strict` or `Lax` depending on the needs of the application. `Strict` will prevent the cookie from being sent on all cross-site requests, while `Lax` allows cookies to be sent when the user navigates to the URL from an external site.

Steps

1. Identify all places in the code where cookies are being set.
2. Add the 'SameSite' attribute to the 'Set-Cookie' header.
3. Set the 'SameSite' attribute to 'Strict' or 'Lax' depending on your needs. 'Strict' will prevent the cookie from being sent by the browser to the target site in all cross-site browsing context, even when following a regular link. 'Lax' allows the cookie to be sent when the user navigates to the cookie's origin site.
4. Test the application to ensure that the changes do not break any functionality and that the cookies are being set correctly with the 'SameSite' attribute.

Secure Code Example

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

shelf.Response handleRequest(shelf.Request request) {
  var response = shelf.Response.ok('Hello, World!');
  return response.change(headers: {
    'Set-Cookie': 'sessionId=123456; Secure; HttpOnly; SameSite=Strict'
  });
}

The original code was setting a cookie without the `SameSite` attribute. This attribute is crucial for preventing cross-site request forgery (CSRF) attacks. It asserts that a cookie must not be sent with cross-origin requests, providing some protection against cross-site request forgery attacks. In the fixed code, we have added the `SameSite` attribute to the `Set-Cookie` header and set it to `Strict`. This means the cookie will only be sent in a first-party context, i.e., it is sent only if the URL of the request matches the cookie's domain. This is the most secure setting, but it might not be suitable for all applications. If your application needs to send cookies with cross-origin requests, you can set `SameSite` to `Lax`. Remember to test your application thoroughly after making these changes to ensure that no functionality is broken and that the cookies are being set correctly with the `SameSite` attribute.

References

Last updated

2023/09/18