NodeJS - GraphQL Mutations

Running the app on Docker

$ sudo docker pull blabla1337/owasp-skf-lab:js-graphql-mutations

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

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
    author_id
  }
}

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

const mutationType = new graphql.GraphQLObjectType({
  name: "Mutation",
  fields: {
    createPost: {
      type: PostType,
      args: {
        title: {
          type: new graphql.GraphQLNonNull(graphql.GraphQLString),
        },
        body: {
          type: new graphql.GraphQLNonNull(graphql.GraphQLString),
        },
        author_id: { type: new graphql.GraphQLNonNull(graphql.GraphQLID) },
      },
      resolve: (root, { title, body, author_id }) => {
        return new Promise((resolve, reject) => {
          database.run(
            "INSERT INTO Posts (title, body, author_id) VALUES (?,?,?);",
            [title, body, author_id],
            (err) => {
              if (err) {
                reject(null);
              }
              database.get("SELECT last_insert_rowid() as id", (err, row) => {
                resolve({
                  id: row["id"],
                  title: title,
                  body: body,
                  author_id: author_id,
                });
              });
            }
          );
        });
      },
    },
  },
});

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 create posts as another user:

Bingo! We have create a new post as another user. Let's refresh the page:

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