In this apprentice-level lab, we will exploit a website with a CORS vulnerability that trusts the “null” origin to obtain a user’s private credentials.
Upon logging in with the given credentials, we visit the account details page and check the response headers of the request to /accountDetails that fetches the user’s API key:
HTTP/1.1 200 OK
Access-Control-Allow-Credentials: true
Content-Type: application/json; charset=utf-8
Connection: close
Content-Length: 149
{
"username": "wiener",
"email": "",
"apikey": "JQ7ufLKKzNoI4ahWKAKWBG5eP64wgwJW",
"sessions": [
"cdmflpOO6psYIp3novWUytbSDM9i68X1"
]
}
We can see that the Access-Control-Allow-Credentials: true is present, let’s try to duplicate this request and change the Origin header to something like Origin:
HTTP/1.1 200 OK
Access-Control-Allow-Credentials: true
Content-Type: application/json; charset=utf-8
Connection: close
Content-Length: 149
{
"username": "wiener",
"email": "",
"apikey": "JQ7ufLKKzNoI4ahWKAKWBG5eP64wgwJW",
"sessions": [
"cdmflpOO6psYIp3novWUytbSDM9i68X1"
]
}
The Origin set in the request headers is not present in the Access-Control-Allow-Origin response headers, this could mean that the server does not have CORS vulnerabilities, let's try setting the Origin header to null :
HTTP/1.1 200 OK
Access-Control-Allow-Origin: null
Access-Control-Allow-Credentials: true
Content-Type: application/json; charset=utf-8
Connection: close
Content-Length: 149
{
"username": "wiener",
"email": "",
"apikey": "JQ7ufLKKzNoI4ahWKAKWBG5eP64wgwJW",
"sessions": [
"cdmflpOO6psYIp3novWUytbSDM9i68X1"
]
}
The null Origin set in the request headers is present in the Access-Control-Allow-Origin response headers, this confirms us that this request has a CORS vulnerability via null origin, let's use the reading material's sandboxed iframe template to craft our exploit so that the request is sent with the Origin header set to null:
