Frame Buster Buster … buster code needed

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

Well, you can modify the value of the counter, but that is obviously a brittle solution. You can load your content via AJAX after you have determined the site is not within a frame - also not a great solution, but it hopefully avoids firing the on beforeunload event (I am assuming).

Edit: Another idea. If you detect you are in a frame, ask the user to disable javascript, before clicking on a link that takes you to the desired URL (passing a querystring that lets your page know to tell the user that they can re-enable javascript once they are there).

Edit 2: Go nuclear - if you detect you are in a frame, just delete your document body content and print some nasty message.

Edit 3: Can you enumerate the top document and set all functions to null (even anonymous ones)?

Answer 2

Considering current HTML5 standard that introduced sandbox for iframe, all frame busting codes that provided in this page can be disabled when attacker uses sandbox because it restricts the iframe from following:

allow-forms: Allow form submissions.
allow-popups: Allow opening popup windows.
allow-pointer-lock: Allow access to pointer movement and pointer lock.
allow-same-origin: Allow access to DOM objects when the iframe loaded form same origin
allow-scripts: Allow executing scripts inside iframe
allow-top-navigation: Allow navigation to top level window

Please see: http://www.whatwg.org/specs/web-apps/current-work/multipage/the-iframe-element.html#attr-iframe-sandbox

Now, consider attacker used the following code to host your site in iframe:

<iframe src="URI" sandbox></iframe>

Then, all JavaScript frame busting code will fail.

After checking all frame busing code, only this defense works in all cases:

<style id="antiClickjack">body{display:none !important;}</style>
<script type="text/javascript">
   if (self === top) {
       var antiClickjack = document.getElementById("antiClickjack");
       antiClickjack.parentNode.removeChild(antiClickjack);
   } else {
       top.location = self.location;
   }
</script>

that originally proposed by Gustav Rydstedt, Elie Bursztein, Dan Boneh, and Collin Jackson (2010)

Answer 3

setInterval and setTimeout create an automatically incrementing interval. Each time setTimeout or setInterval is called, this number goes up by one, so that if you call setTimeout, you'll get the current, highest value.

   var currentInterval = 10000;
   currentInterval += setTimeout( gotoHREF, 100 );
   for( var i = 0; i < currentInterval; i++ ) top.clearInterval( i );
   // Include setTimeout to avoid recursive functions.
   for( i = 0; i < currentInterval; i++ )     top.clearTimeout( i );

   function gotoHREF(){
           top.location.href = "http://your.url.here";
   }

Since it is almost unheard of for there to be 10000 simultaneous setIntervals and setTimeouts working, and since setTimeout returns "last interval or timeout created + 1", and since top.clearInterval is still accessible, this will defeat the black-hat attacks to frame websites which are described above.

Answer 4

if (top != self) {
  top.location.replace(location);
  location.replace("about:blank"); // want me framed? no way!
}

Answer 5

All the proposed solutions directly force a change in the location of the top window. What if a user wants the frame to be there? For example the top frame in the image results of search engines.

I wrote a prototype where by default all inputs (links, forms and input elements) are disabled and/or do nothing when activated.

If a containing frame is detected, the inputs are left disabled and a warning message is shown at the top of the page. The warning message contains a link that will open a safe version of the page in a new window. This prevents the page from being used for clickjacking, while still allowing the user to view the contents in other situations.

If no containing frame is detected, the inputs are enabled.

Here is the code. You need to set the standard HTML attributes to safe values and add additonal attributes that contain the actual values. It probably is incomplete and for full safety additional attributes (I am thinking about event handlers) will probably have to be treated in the same way:

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN">
<html>
  <head>
    <title></title>
    <script><!--
      function replaceAttributeValuesWithActualOnes( array, attributeName, actualValueAttributeName, additionalProcessor ) {
        for ( var elementIndex = 0; elementIndex < array.length; elementIndex += 1 ) {
          var element = array[ elementIndex ];
          var actualValue = element.getAttribute( actualValueAttributeName );
          if ( actualValue != null ) {
            element[ attributeName ] = actualValue;
          }

          if ( additionalProcessor != null ) {
            additionalProcessor( element );
          }
        }
      }

      function detectFraming() {
        if ( top != self ) {
          document.getElementById( "framingWarning" ).style.display = "block";
        } else {
          replaceAttributeValuesWithActualOnes( document.links, "href", "acme:href" );

          replaceAttributeValuesWithActualOnes( document.forms, "action", "acme:action", function ( form ) {
            replaceAttributeValuesWithActualOnes( form.elements, "disabled", "acme:disabled" );
          });
        }
      }
      // -->
    </script>
  </head>
  <body onload="detectFraming()">
    <div id="framingWarning" style="display: none; border-style: solid; border-width: 4px; border-color: #F00; padding: 6px; background-color: #FFF; color: #F00;">
      <div>
        <b>SECURITY WARNING</b>: Acme App is displayed inside another page.
        To make sure your data is safe this page has been disabled.<br>
        <a href="framing-detection.html" target="_blank" style="color: #090">Continue working safely in a new tab/window</a>
      </div>
    </div>
    <p>
      Content. <a href="#" acme:href="javascript:window.alert( 'Action performed' );">Do something</a>
    </p>
    <form name="acmeForm" action="#" acme:action="real-action.html">
      <p>Name: <input type="text" name="name" value="" disabled="disabled" acme:disabled=""></p>
      <p><input type="submit" name="save" value="Save" disabled="disabled" acme:disabled=""></p>
    </form>
  </body>
</html>

Answer 6

We have used the following approach in one of our websites from http://seclab.stanford.edu/websec/framebusting/framebust.pdf

<style>
 body { 
 display : none   
}
</style>
<script>
if(self == top) {
document.getElementsByTagName("body")[0].style.display = 'block';
}
else{
top.location = self.location;
}
</script>