Frame busting and clickjacking prevention

Clickjacking allows an attacker to trick your users into clicking parts of your interface without their consent. A simple way to describe describe this is, an attacker will embed your application in their site as an iframe. On top of the iframe they can show a completely different interface. You’re thinking you’re clicking buttons on your own interface, while in fact you are hitting the ‘Delete my account’ button in for example GMail.

Because this technique completely operates with frames, it can be circumvented by using a ‘Frame busting’ technique. As a bonus, this will also disallow for example Digg to steal and monetize your content.

Frame busting can be achieved with a simple javascript technique:

<script type="text/javascript">
if (top !== self) top.location.replace(self.location.href);
</script>

Security through javascript?

If you think this sounds like a bad idea, you are probably right. Users might simply have javascript disabled, and I also don’t like relying on UI developers too much to implement preventive security measures (although I realize in most cases you do have to).

In Internet Explorer the situation is worse, IE allows you to specify the non-standard attribute security=”restricted”:


<iframe src="http://www.rooftopsolutions.nl/" security="restricted"></iframe>

This attribute tells IE to not allow executing of javascript in the iframe, which actually is not a bad security measure for other types of attacks. In this case however, it allows the attacker to disable the framebusting script.

X-Frame-Options

Thankfully, Internet Explorer 8 introduces a new feature that allows the site owner to disallow frames altogether, which is in my opinion an even better protection mechanism, because it doesn’t rely on javascript to be executed.

The name of the http header is specified as such:

X-FRAME-OPTIONS: SAMEORIGIN
X-FRAME-OPTIONS: DENY

You only have to specify one of these two, ‘sameorigin’ means the page can only be framed from an html page hosted on the same domain, deny will kill framing altogether.

PHP example:

<?php
header('X-FRAME-OPTIONS: DENY');
?>

Firefox also appears to have started implementing this feature, and there’s a feature request for webkit open as well.

Protecting yourself

Unfortunately you can safely assume most sites don’t implement either of these security measures. For firefox users I would therefore strongly recommend using the NoScript plugin. Not only does it implement the X-FRAME-OPTIONS for firefox, it also actively detects clickjacking attempts.

Reference: hackademix.net