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Clickjacking

Tuesday, October 07, 2008

Clickjacking Details, Analysis, and Advice

By Rich

Looks like the cat is out of the bag. Someone managed to figure out the details of clickjacking and released a proof of concept against Flash. With the information out in public, Jeremiah and Robert are free to discuss it.

I highly recommend you read Robert’s post, and I won’t try and replicate the content. Rather, I’d like to add a little analysis. As I’ll spell out later, this is a serious browser flaw (phishers will have a field day), but in the big picture of risk it’s only moderate.

  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. The fixes generally break other things.

After spending some time talking with Robert about it, I’d rate clickjacking as a serious web browser issue (it isn’t quite a traditional vulnerability), but only a moderate risk overall. It will be especially useful for phishers who draw unsuspecting users to their sites, or when they XSS a trusted site (which seems to be happening WAY too often).

Here’s how to reduce your risk as a user:

  1. Use Firefox/NoScript and check the setting to restrict iFrames.
  2. Don’t stay logged in to sensitive sites if you are browsing around (e.g., your bank, Amazon, etc.). Use something like 1Password or RoboForm to make your life easier when you have to enter passwords.
  3. Use different browsers for different things, as I wrote about here. At a minimum, dedicate one browser just for your bank.

As a website operator, you can also reduce risks:

  1. Use iFrame busting code as much as possible (yes, that’s a tall order).
  2. For major transactions, require user interaction other than a click. For example, my bank always requires a PIN no matter what. An attacker may control my click, but can’t force that PIN entry.
  3. Mangle/generate URLs. If the URL varies per transaction, the attacker won’t necessarily be able to force a click on that page.

Robert lays it out:

From an attacker”s perspective the most important thing is that a) they know where to click and b) they know the URL of the page they want you to click, in the case of cross domain access. So if either one of these two requirements aren”t met, the attack falls down. Frame busting code is the best defense if you run web-servers, if it works (and in our tests it doesn’t always work). I should note some people have mentioned security=restricted as a way to break frame busting code, and that is true, although it also fails to send cookies, which might break any significant attacks against most sites that check credentials.

Robert and Jeremiah have been very clear that this is bad, but not world-ending. They never meant for it to get so hyped, but Adobe’s last-minute request to not release caught them off guard. I spent some time talking with Robert about this in private and kept feeling like I was falling down the rabbit hole- every time I tried to think of an easy fix, there was another problem or potential consequence, in large part because we rely on the same mechanisms as clickjacking for normal website usability.

–Rich

Friday, October 03, 2008

Friday Summary

By Adrian Lane

The Securosis team is attempting to regroup and prepare for a busy Q4. It took three full days, but I am fully migrated into the Mac Universe and engaged in a couple of research projects. Now productive, I can finally start work on a couple research projects. Rich has left HQ in search of coffee, quiet and a security muse while he catches up on writing projects and white papers. But even though we have a short term ban on travel and conferences, there is a lot to talk about. Here is our summary of this weeks blogs, news and events.

Webcasts, Podcasts, and Conferences:

Favorite Securosis Posts:

  • Rich: Impact of the Economic Crisis on Security. It doesn’t matter if you are a vendor or practitioner, we’ll feel the effects of this crisis, but in a predictable way.
  • Adrian: Email Security. It’s getting cheaper, faster and easier to implement, but with some potential privacy issues depending on how you go about it.

Favorite Outside Posts:

  • Adrian: Brian Krebs post on lawsuits against ‘Scareware Purveyors’. Finally. Infecting someone’s machine with spyware and using it as a marketing and sales conduit is akin to stealing in my book. Now if they would only go after the purveyors of this scare tactic.
  • Rich: Fyodor explains (probably) the looming TCP attack. Fyodor, creator of NMAP, does an excellent job of explaining how the big TCP DoS attack likely works.

Top News:

  • The recovery bill. Law makers look panicked, and the market goes down every time they get close to a ‘solution’.
  • The TCP Denial of Service attack. Nothing to panic about, and we’ll write more on it, but very interesting.

Blog Comment of the Week:

Chris Pepper’s comment on Rich’s “Statistical Distractions” post:

[snip]... I refuse to use unencrypted email, but that”s to the SMTP/IMAP/POP/webmail server. But for email we have to keep in mind that the second hop – to the destination SMTP server – is almost always plaintext (unencrypted SMTP). So it’s more about protecting the account credentials than about protecting the email itself, but someone gaining full access to my whole multi-gigabyte mail store would really really suck. …[/snip]

Now, I am off to The Office for the Securosis weekly staff meeting. We hope you all have a great weekend.

–Adrian Lane

Tuesday, September 30, 2008

Clickjacking The Network Security Podcast

By Rich

We had a killer episode of the Network Security Podcast this week as Jeremiah Grossman and Robert “Rsnake” Hansen joined us to talk a bit about their new clickjacking exploit. I definitely had some fun on this one, even though Jeremiah and Robert couldn’t dig too deeply into the details.

We also managed to sneak in a bit on open source voting, and the top 10 ways to know you’ve been exploited.

But mostly, you want to hear is making fun of each other.

This was also one of our first episodes we streamed live. Although we record at irregular times, we plan on live streaming as much as we can. Just keep an eye on us on twitter (rmogull or netsecpodcast) for a few hours warning if you want to listen in and harass us over IM.

You can download the episode here, and full show notes are at NetSecPodcast.com.

–Rich