Researcher Lance James has been busy devising ways to play tricks on some of the world's bigger websites using an exotic attack known as CSRF, or cross site request forgery. While his exploits amount to little more than pranks, they point to the very sobering realization that the net isn't a very secure place.
One proof-of-concept attack targets users of Hulu.com. Clicking on it while logged in to the online provider of TV shows causes Fox Network's Family Guy to be added as a subscription and the documentary Air Force One to be put in the queue. This happens behind the scenes.
Similarly, readers who click here while logged in to Netflix will find the movie Sneakers added to their queue without ever being asked for permission. The link never actually displays a Netflix page, so it's likely users will have no idea the addition has been made until the DVD shows up in their mailbox.
"I can probably figure out how to make you buy my book without realizing it," says James, who is a researcher at Secure Science Corp and the author of Phishing Exposed. (A demonstration of just that attack is available here). "It's kind of like a magic trick when you can do things to people's computers underneath."
James likens CSRF attacks to the oft-repeated tactic used in Chuck Norris movies, where the protagonist breaches his enemy's well-fortified compound by hiding himself under the chassis of a trusted vehicle as it enters. In much the same way, CSRFs are able to trick websites into executing unauthorized commands by exploiting the trust they have for the user.
(Also referred to as session riding and one-click attacks, CSRFs are not to be confused with XSS, or cross-site scripting attacks, in which an attacker injects hostile code and content into a trusted website).
James says sites including MySpace, Twitter, and Google have gone to great lengths to prevent CSRF attacks on their properties, often by requiring users to re-enter passwords before making sensitive changes. But plenty of sites see such safeguards as a potential annoyance to their users and forgo them. And so, he says, it's not hard to spot CSRF vulnerabilities of some of the web's most popular sites.
While the three proofs-of-concept demonstrate relatively innocuous attacks, this does not have to be the case. For anyone logged in to Tivo.com, the link here will silently change the email address associated with the account with no warning at all. (Be sure to change it back if you clicked on it while logged in). An attacker could exploit this weakness in a two-step attack that changes the email address and then uses it to reset the account password.
Plenty of other websites have been bitten by the CSRF bug, including Google, which in September 2007 was found to suffer from a vulnerability that could be used to steal user pictures stored using its Picasa photo organizer.
But even fairly innocuous exploits such as those that add a movie to a user's Netflix queue may have unexpected consequences, given that websites of its size often sell anonymized user selections to marketers.
"If that stuff becomes inaccurate or untrustworthy, the value of the product to Netflix actually goes down," James says. ®