Java - GraphQL Mutations

Running the app on Docker

$ sudo docker pull blabla1337/owasp-skf-lab:java-graphql-mutation

$ sudo docker run -ti -p 127.0.0.1:5000:5000 blabla1337/owasp-skf-lab:java-graphql-mutation

Now that the app is running let's go hacking!

Reconnaissance

The application implements a very basic mutation to create a new post on the blog. The mutation used is the following

mutation {
  createPost(title: "This is a new title", body: "This is a new post", author_id: 2) {
    id
    title
    body
  }
}

If we look at the code we have a class CreatePost that will implement our logic to create a post.

public Post createPost(String title, String body, int user_id) throws org.hibernate.exception.GenericJDBCException{
    Post post = new Post();
    post.setTitle(title);
    post.setBody(body);
    post.setUser(new User(user_id));
    postRepository.save(post);
    return post;
}

The method mutate will just get the new Post object and insert an instance in the database.

Exploit

There are many ways we could exploit this, one would be to delete any post we want. If there is a createPost class there might be another class called deletePost, let's try:

Bingo! Post with id:4 was deleted. If we go back and refresh the application:

You could, of course, achieve the same goal with burp. What else can you exploit using this vulnerability?

Additional resources

GraphQL - OWASP Cheat Sheet Series