GraphQL IDOR

The application uses GraphQL to retrieve Users and Posts for the defdev.eu new blog.

Run the application

docker build . -t graphql/idor && docker run -ti -p 5000:5000 graphql/idor

Great now the app is running. Browse to http://0.0.0.0:5000/

Discovery

As soon as we browse on http://0.0.0.0:5000 we see that now our app implements a login screen to support multiple users

We already registered a user , the famous Jhon Doe and we can authneticate with the credentials

jhondoe
password1

Now that we are in, we discover that every time a user logs in, the application sets a cookie called

X-Api-Key

that is used by the app to authenticate the keep the session active and recognize the user.

The API key can be used also to retrieve info from the blog. But this is another story.

What we want to do, is to find a way to authenticate us other users using an IDOR vulnerability.

Exploitation

What's new in this application is that an user can see his settings, browsing to the page:

http://0.0.0.0:5000/settings

of course only if authenticated. But how does this page retrieve the information is crucial. If we intercept the traffic we can see that the application sends a GraphQL query to the backend to ask for the information we see in the page. The query looks like this:

{
 					singleUser (user: 1) {
    				apiKey
    				name
    				surname
    				dateOfBirth
  				}
			}

Knowing that, use the IDOR vulnerability to authenticate as another user

Fix

Implement authorization on graphql endpoint. Although authenticated users could query the information, you should validate that the requestor of the information is actually the legit one, and use UUID instead of ID as Int.