GraphQL Attacks

Finding GraphQL Endpoints

• Universal query - query{__typename}
• Common endpoints:
  • /graphql, /api, /api/graphql, /graphql/api, graphql/graphql
  • All of the above with v1 or v2 in the path start/end
  • If no endpoints pop up, try using alternative HTTP methods (non-POST) with the universal query

Exploiting Unsanitized Arguments

• Think common web vulns here
• Example:
  • Pretend query is query {products {id name listed}}
  • If this returns products 1, 2, and 4, we can try to IDOR product 3 with
    • query {products(id: 3) {id name listed}}

Discovering Schema Information

• Suggestions
  • Apollo GraphQL will suggest amendments when errors occur, like There is no entry for 'productInfo'. Did you mean 'productInformation' instead?
  • These can be used to glean information about the schema
  • Clairvoyance uses suggestions to recover the schema
• Introspection queries
  • Built-in function that allows querying schema information
    • query{__schema}
    • {"query": "{__schema{queryType{name}}}"}
  • Description fields can sometimes have sensitive info
  • Introspection query can be sent via {right click} > GraphQL > Set introspection query
    • Can return lots of information, so right click the response and Save GraphQL queries to site map
    • Can use online visualizers, but it didn’t show a mutation query
      • http://nathanrandal.com/graphql-visualizer/ (don’t use on sensitive data, run visualizer locally)
• Mutation queries
  • Will have variables parameter where input is specified

Bypassing Introspection Defenses

• Sometimes, introspection queries won’t run due to being disabled
• Developers sometimes disable introspection by excluding __schema{ keyword
  • Flawed regex can be defeated by adding spaces/new lines/comments after __schema (which are ignored by GraphQL)
• Introspection may sometimes only be disabled over POST, so try GET requests or POST requests with content-type of x-www-form-urlencoded
  • ?query=query%7B__schema%7BqueryType%7Bname%7D%7D%7D
  • %0A for a newline

Bypassing Rate Limiting

• Many endpoints will have a rate limiter in place, and will often be based on the number of HTTP requests received (as opposed to the number of operations performed)
  • Network level instead of application level
• This means that we can do a massive brute force of one object/query in a single request using aliases:

query isValidDiscount($code: Int) {
    isvalidDiscount(code:$code){
        valid
    }
    isValidDiscount2:isValidDiscount(code:$code){
        valid
    }
    isValidDiscount3:isValidDiscount(code:$code){
        valid
    }
}

• Python script to generate JSON-friendly aliases given a file with a list of words (brute forcing usernames example):
  • Replace [mutations_code_here] with \n{mutations}\n (Github markdown issue)

import json
with open("wordlist.txt") as f:
    passwords = [line.strip() for line in f]
mutations = "\n".join(
    f'bruteforce{i}: [function](input: ) '
    for i, pw in enumerate(passwords)
)

graphql_query = {
    "query": f"mutation "
}

print(json.dumps(graphql_query, indent=2))

GraphQL CSRF

• Arise when GraphQL endpoints don’t validate content type of requests and CSRF tokens not implemented
  • POST requests with content type of application/json are secure as long as content type is validated
• Can use GET requests or requests with x-www-form-urlencoded, since they can be sent by a browser
  • Either way, need to format it in a URL encoded parameter format (with = and &)
    • Make sure that {, }, and : (along with other special chars) are URL encoded