The True Danger of XSS and CSRF

In our one-day training classes and conference talks we make judicious use of videos to demonstrate concepts. One of the most popular videos illustrates the true danger of Cross-Site Scripting (XSS) combined with Cross-Site Request Forgery (CSRF). We constructed a fake bank site and demonstrated that a single XSS vulnerability and money transfer functionality in the bank site could result in a user losing money just by visiting another site. In the example, the bank site isn’t over SSL but SSL would not prevent this attack in any way.

The malicious site in our example is completely attacker-controlled, but in reality the malicious site could actually be a Flash ad in a trusted site, Facebook / Myspace / LinkedIn applications or other mashups running untrusted code, or even malicious code running in another trusted site like a bulletin board.

In our example, the user visits the bank site and the attacker site in two browser tabs at the same time. In reality, the victim is exposed for the entire duration of his/her session on the server. That means if a user simply closes their browser window and doesn’t actually logout of the banking application, they are still vulnerable for a period of time – usually 15-30 minutes.