Javascript to prevent clickjacking

Question

I have this Javascript snippet in my application to prevent clickjacking:

<script language="javascript" type="text/javascript">
     var style = document.createElement('style');
     style.type = "text/css";
     style.id = "antiClickjack";
     style.innerHTML = "body{display:none !important;}";
     document.head.appendChild(style);

     if (self === top) {
         var antiClickjack = document.getElementById("antiClickjack");
         antiClickjack.parentNode.removeChild(antiClickjack);
     } else {
         top.location = self.location;
     }
</script>

Basically, it creates a style element (CSS on the fly) to hide the body of the current page by default. Then, if it doesn't detect clickjacking, it deletes it. So, doing it this way, everyone who doesn't have Javascript can see the page too (although they won't be protected from clickjacking).

It works for every browser except for Internet Explorer, which throws a Unknown runtime error exception. Does someone have a suggestion on how to fix this?

Thanks :-)

Answer 1

In the document HEAD element, add the following:

<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>

Answer 2

You can't set the content of a <style> element via innerHTML. I think the correct property name is cssText but I'll have to check MSDN.

edit — yup that's it.

Thus your code can do this:

 var style = document.createElement('style');
 style.type = "text/css";
 style.id = "antiClickjack";
 if ('cssText' in style)
   style.cssText = "body{display:none !important;}";
 else
   style.innerHTML = "body{display:none !important;}";