X-Frame-Options - How to Combat Clickjacking

In today's world, security is a top concern for website owners and administrators. One of the biggest threats to website security is clickjacking, also known as UI redress attack. This is a technique where a malicious website overlays its own content on top of a legitimate website, tricking the user into clicking buttons or links that they didn't intend to.

To combat this threat, website administrators can use the X-Frame-Options header.

HTTP security headers provide yet another layer of security by helping to mitigate attacks and security vulnerabilities by telling your browser how to behave. In this post we will be diving more in-depth into X-Frame-Options (XFO), which is a header that helps to protect your visitors against clickjacking attacks. It is recommended that you use the X-Frame-Options header on pages which should not be allowed to render a page in a frame.

What is X-Frame-Options?

X-Frame-Options (XFO), is an HTTP response header, also referred to as an HTTP security header, which has been around since 2008. In 2013 it was officially published as RFC 7034, but is not an internet standard. This header tells your browser how to behave when handling your site's content. The main reason for its inception was to provide clickjacking protection by not allowing rendering of a page in a frame. This can include rendering of a page in a <frame>, <iframe>, or <object>. Iframes are used to embed and isolate third party content into a website. Examples of things that use iframes might include social media sharing buttons, Google Maps, video players, audio players, third party advertising, and even some OAuth implementations.

Clickjacking

So what exactly is clickjacking? Clickjacking is an attack that occurs when an attacker uses a transparent iframe in a window to trick a user into clicking on a CTA, such as a button or link, to another server in which they have an identical looking window. The attacker in a sense hijacks the clicks meant for the original server and sends them to the other server. This is an attack on both the visitor themselves and on the server.

Here are a couple possible known exploits or uses for clickjacking.

• Tricking users into making their social networking profile information public
• Sharing or liking links on Facebook
• Clicking Google Adsense ads to generate pay per click revenue
• Making users follow someone on Twitter or Facebook
• Downloading and running a malware (malicious software) allowing to a remote attacker to take control of others computers
• Getting likes on Facebook fan page or +1 on Google Plus
• Playing YouTube videos to gain views

Clickjacking is easy to implement, and if your site has actions that can be done with a single click, then most likely it can be clickjacked. It might not be as common as cross site scripting or code injection attacks, but it is still another vulnerability that exists.

X-Frame-Options directives

The X-Frame-Options header has three different directives in which you can choose from. These must be sent as an HTTP header, as the browser will ignore if found in a META tag. It is also important to note that certain directives are only supported in certain browsers. See browser support further below in this post. While it is not required to send this response header across your entire site, it is best practice to at least enable it on pages that need it.

1. deny directive

The deny directive completely disables the loading of the page in a frame, regardless of what site is trying. Below is what the header request will look like if this is enabled.

X-Frame-Options: deny

This might be a great way to lock down your site, but it will also break a lot of functionality. The following two directives below are more common use cases for a typical website.

Examples of sites currently using the deny directive:

• Facebook
• GitHub

2. sameorigin directive

The sameorigin directive allows the page to be loaded in a frame on the same origin as the page itself. Below is what the header request will look like if this is enabled.

X-Frame-Options: sameorigin

We have the sameorigin directive enabled on this website. With this directive enabled, only our website is allowed to embed an iframe of one of our pages. This is probably the most commonly used directive out of the three. It is a good balance between functionality and security.

It is also important to note that if a browser or plugin can not reliably determine whether the origin of the content and the frame have the same origin, this must be treated as deny.

Examples of sites currently using the sameorigin directive:

• Twitter
• Amazon
• eBay
• LinkedIn

3. allow-from uri directive

The allow-from uri directive allows the page to only be loaded in a frame on the specified origin and or domain. Below is what the header request will look like if this is enabled.

X-Frame-Options: allow-from https://www.example.com/

This allows you to lock down your site to only trusted origins. But be careful with this directive. If you apply it and the browser does not support it, then you will have NO clickjacking defense in place.

Enabling X-Frame-Options header

The X-Frame-Options header is easy to implement and only requires a slight web server configuration change. You might also want to check to make sure you don't already have the header enabled. Here are a couple easy ways to quickly check.

Enable on Nginx

To enable the X-Frame-Options header on Nginx simply add it to your server block config.

add_header X-Frame-Options "sameorigin" always;

Enable on Apache

To enable on Apache simply add it to your httpd.conf file (Apache config file).

header always set X-Frame-Options "sameorigin"

Enable on IIS

To enable on IIS simply add it to your site's Web.config file.

<system.webServer>
    ...

    <httpProtocol>
        <customHeaders>
            <add name="X-Frame-Options" value="sameorigin" />
        </customHeaders>
    </httpProtocol>

    ...
</system.webServer>

X-Frame-Options browser support

It is important to realize that not all browsers support the allow-from directive. So be careful if you are using that. All modern browsers do support the deny and sameorigin directives. For legacy browsers your best solution currently is to use what they call a frame-breaker or frame-buster.

Another newer option and or alternative you have to using XFO is to use the Content Security Policy and frame-ancestors directive. This will most likely eventually replace XFO altogether. One major benefit to this directive is that it allows you to authorize multiple domains, but there is no support for Internet Explorer:

You could however use both the X-Frame-Options and frame-ancestors together.

Summary

Hopefully now you understand a little more about what the X-Frame-Options HTTP response header does and how it can help prevent clickjacking. As seen above, this is very easy to implement. We use security headers on our websites and we encourage you to do the same. Together we can make the web a more secure place and help boost the security header usage numbers.