Excessive trust in client-side controls


This lab doesn’t adequately validate user input. You can exploit a logic flaw in its purchasing workflow to buy items for an unintended price.

Reproduction and proof of concept

  1. With Burp running, log in with wiener:peter and attempt to buy the leather jacket. The order is rejected because you do not have enough store credit.

  2. In Burp, go to Proxy -> HTTP history and study the order process. Notice that when you add an item to the cart, the corresponding request contains a price parameter. Send the POST /cart request to Burp Repeater.

  3. In Burp Repeater, change the price to an arbitrary integer and send the request. Refresh the cart and confirm that the price has changed based on your input.

  4. Repeat this process to set the price to any amount less than your available store credit.

  5. Complete the order to solve the lab.


An attacker will need to log in; study the order process; and buy a “Lightweight l33t leather jacket” for way less than intended.