Checking Third-Party iFrame Content [duplicate]

Question

Let's say you don't want other sites to "frame" your site in an <iframe>:

<iframe src="http://example.org"></iframe>

So you insert anti-framing, frame busting JavaScript into all your pages:

/* break us out of any containing iframes */
if (top != self) { top.location.replace(self.location.href); }

Excellent! Now you "bust" or break out of any containing iframe automatically. Except for one small problem.

As it turns out, your frame-busting code can be busted, as shown here:

<script type="text/javascript">
    var prevent_bust = 0  
    window.onbeforeunload = function() { prevent_bust++ }  
    setInterval(function() {  
      if (prevent_bust > 0) {  
        prevent_bust -= 2  
        window.top.location = 'http://example.org/page-which-responds-with-204'  
      }  
    }, 1)  
</script>

This code does the following:

• increments a counter every time the browser attempts to navigate away from the current page, via the window.onbeforeunload event handler
• sets up a timer that fires every millisecond via setInterval(), and if it sees the counter incremented, changes the current location to a server of the attacker's control
• that server serves up a page with HTTP status code 204, which does not cause the browser to navigate anywhere

My question is -- and this is more of a JavaScript puzzle than an actual problem -- how can you defeat the frame-busting buster?

I had a few thoughts, but nothing worked in my testing:

• attempting to clear the onbeforeunload event via onbeforeunload = null had no effect
• adding an alert() stopped the process let the user know it was happening, but did not interfere with the code in any way; clicking OK lets the busting continue as normal
• I can't think of any way to clear the setInterval() timer

I'm not much of a JavaScript programmer, so here's my challenge to you: hey buster, can you bust the frame-busting buster?

Answer 1

FWIW, most current browsers support the X-Frame-Options: deny directive, which works even when script is disabled.

IE8: IE8 Security Part VII: ClickJacking Defenses

Firefox (3.6.9)

• X-FRAME-OPTIONS header against "UI Redressing" AKA Clickjacking
• X-Frame-Options | MDN

Chrome/Webkit

• Security in Depth: New Security Features
• Changeset 42333 in webkit