Newfangled cookie attack steals/poisons website creds
Google, Facebook risk
A security researcher has discovered a weakness in a core browser protocol that compromises the security of Google, Facebook, and other websites by allowing an attacker to tamper with the cookies they set.
The weakness stems from RFC 2965, which dictates that browsers must allow subdomains (think www.google.com) to set and read cookies for their parent (google.com). The specification also states that if a cookie for a subdomain doesn't already exist, the browser should use the cookie belonging to the parent instead. The arrangement makes it possible for attackers to steal or even alter the cookies that websites use to authenticate their users. Attackers would first have to identify an XSS, or cross-site scripting, bug in some part of the site they are targeting. But because virtually any subdomain will suffice, the scenario isn't unrealistic, two web security experts said.
"Most websites actually will store session IDs in a cookie and that's actually how they keep track of users throughout the use of their website," said Mike Bailey, a senior researcher for Foreground Security who first documented the flaw at last month's Toorcon hacker conference. "Using the same techniques to attack those cookies, I can really damage sessions and cause some problems."
Bailey's paper goes on to demonstrate how he used the technique to bypass a feature Google recently implemented to beef up security on Gmail and other properties. By exploiting a minor vulnerability in sites.google.com, he was able to falsify the contents of his global Google cookie. Google has since fixed the XSS hole in the subdomain.
In turn, that allowed him fool the Google protection, which checks to make sure the value in the cookie matches a hidden parameter of the login page.
http://www.theregister.co.uk/2009/11/04/website_cookie_stealing/