SSRF with filter bypass via open redirection vulnerability

Description

This lab has a stock check feature which fetches data from an internal system.

Reproduction and proof of concept

1. Visit a product, click Check stock, intercept the request in Burp Suite, and send it to Burp Repeater. Click next product (on the site) and send that to Repeater also.

2. Try tampering with the stockApi parameter of the first intercepted request and observe that it isn’t possible to make the server issue the request directly to a different host.

3. For the next product request observe that the path parameter is placed into the Location header of a redirection response, resulting in an open redirection.

4. Create a URL that exploits the open redirection vulnerability, and redirects to the admin interface, and feed this into the stockApi parameter on the stock checker:

5. Observe that the stock checker follows the redirection and shows you the admin page.

6. Amend the path to delete the target user:

Exploitability

An attacker will need to change the stock check URL to access the admin interface at http://192.168.0.12:8080/admin and delete the user carlos. The stock checker has been restricted to only access the local application, so the attacker will need to find an open redirect affecting the application first.