Cyber Soldier | Software Engineer

12 April 2021

Hacker 101 CTF Walkthrough: BugDB v1

by Najam Ul Saqib

In this post, I will be taking you through one of the CTFs on HackerOne named "BugDB v1".

This CTF is focused on the basic concept of GraphQL APIs and how they works. Let's start.

When you open this CTF, a minimal page opens up having a hyper link to GraphiQL



 I first tried using the famous introspection query that usually is used to check the structure of the endpoint

{__schema{queryType{name}mutationType{name}subscriptionType{name}types{...FullType}directives{name description locations args{...InputValue}}}}fragment FullType on __Type{kind name description fields(includeDeprecated:true){name description args{...InputValue}type{...TypeRef}isDeprecated deprecationReason}inputFields{...InputValue}interfaces{...TypeRef}enumValues(includeDeprecated:true){name description isDeprecated deprecationReason}possibleTypes{...TypeRef}}fragment InputValue on __InputValue{name description type{...TypeRef}defaultValue}fragment TypeRef on __Type{kind name ofType{kind name ofType{kind name ofType{kind name ofType{kind name ofType{kind name ofType{kind name ofType{kind name}}}}}}}}


I copied the response from this GraphQL endpoint to GraphQL Voyager in order to better understand the response. The graphical structure received is as follows:

It shows that we have different entities like Bugs,Users etc and obviously Query object containing different queries like we can query for users and bugs. Enough said I played with all these queries in order to find something special but of no avail.

Then I looked into the docs of the GraphQL endpoint (button available at top right corner of the window), after reading through the docs I made a query that was using all the types available in the docs and so I was technically fetching all the information from the endpoint. 

        id,username,bugs {
          edges {
            node {
              text,reporter {

This in response gave me the flag to solve the CTF.


Actually this CTF is more of a introductory CTF to GraphQL so that you can see how graphQL works and understand reading its documentation.

tags: ctf - hackerone - walkthrough