Clickjacking here’s how it works

I’ve posted before about Clickjacking and how scary this is for most Internet users, regardless of which browser you’re using or whether you have Javascript turn on or off. There’s more information about the threat on the Interweb today, including a demo of how the exploit works and some advice on how you can avoid it. First of all, what is clickjacking? There’s a great writeup on Securoris that explains it quite succinctly:

  1. Clickjacking allows someone to place an invisible link/button below your mouse as you browse a regular page. You think you’re clicking on a regular link, but really you are clicking someplace the attacker controls that’s hidden from you. Why is this important? Because it allows the attacker to force you to interact with something without your knowledge on a page other than the one you’ve been looking at. For example, they can hide a Flash application that follows your mouse around, and when you go to click a link it starts recording audio off your microphone. We have protections in browsers to prevent someone from automatically initiating certain actions. Also, many websites rely on you manually pressing buttons for actions like transferring large sums of money out of your bank account.
  2. There are two sides to look at this exploitation- user and website owner. As a user, if you visit a malicious site (either a bad guy site, or a regular site that’s been hit with cross site scripting), the attacker can force you to take a very large range of actions. Anytime you click something, the attacker can redirect that click to the destination of their choice in the context of you as a user. That’s the important part here- it’s like cross site request forgery (really, an enhancement of it) that not only gets you to click, but to execute actions as yourself. That’s why they can get you to approve Flash applications you might not normally allow, or to perform actions on other sites in the background. As with CSRF, if you are logged in someplace the attacker can now do whatever the heck they want as long as they know the XY coordinates of what they want you to click.
  3. As a website owner, clickjacking destroys yet more browser trust. When designing web applications (which used to be my job) we often rely on site elements that require manual mouse clicks to submit forms and such. As Robert (Rsnake) explains in his post, with clickjacking an attacker can circumvent nonces (a random code added to every form so the website knows you clicked submit from that page, and didn’t just try to submit the form without visiting the page, a common attack technique).
  4. Clickjacking can be used to do a lot of different things- launching Flash or CSRF are only the tip of the iceberg.
  5. It relies heavily on iFrames, which are so pervasive we can’t just rip them out. Sure, I turn them off in my browser, but the economics prevent us from doing that on a wide scale (especially since all the advertisers- e.g. Google/Yahoo/MS, will likely fight it).
  6. Clickjacking is very difficult to eliminate, although we can reduce its risk under certain circumstances. Because it doesn’t even rely on Javascript and works with CSS/DHTML, it will take a lot of time, effort, and thought to eliminate.

If that sounded scary, have a look at a video showing one application of the exploit:

If you want to study that further, you can actually run it through it’s paces here.

So, what can be done about this? First of all, it’s worth realising that while it’s a powerful threat, the risk of it happening isn’t that high at the moment. Vendors have started recognising the threat and coming up with solutions for dealing with it. Adobe has come up with a workaround and NoScript has released ClearClick to help address it. It’s only a matter of time before this is quashed too (won’t be easy though)

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