A framekiller is a piece of JavaScript

JavaScript

JavaScript is a prototype-based scripting language that is dynamic, weakly typed and has first-class functions. It is a multi-paradigm language, supporting object-oriented, imperative, and functional programming styles....

 code that doesn't allow a Web page

Web page

A web page or webpage is a document or information resource that is suitable for the World Wide Web and can be accessed through a web browser and displayed on a monitor or mobile device. This information is usually in HTML or XHTML format, and may provide navigation to other web pages via hypertext...

 to be displayed within a frame. A frame is a subdivision of a Web browser window and can act like a smaller window. This kind of script is often used to prevent a frame from an external Web site being loaded from within a frameset without permission.

The typical source code for a framekiller script is:


There are many variations of this script. This example is cross-browser compatible, avoids deprecated objects, and uses replace which preserves the user's back-button.
Comparing object references, top, self and location directly is slightly more efficient, and succinct.

Framekiller Killers

The above framekiller can be prevented from working with the following JavaScript along with a server which responds with a HTTP/1.1 204 No Content, as discovered in this blog. Just place the following code in the top frame. It works because in most browsers a 204 HTTP response will do nothing, meaning it will leave us on the current page. But the request attempt will override the previous frame busting attempt, rendering it useless.

var prevent_bust = 0;

// Event handler to catch execution of the busting script.
window.onbeforeunload = function { prevent_bust++ };

// Continuously monitor whether busting script has fired.
setInterval(function {
if (prevent_bust > 0) { // Yes: it has fired.
prevent_bust -= 2; // Avoid further action.
// Get a 'No Content' status which keeps us on the same page.
window.top.location = 'http://server-which-responds-with-204.example.com';
}
}, 1);

Alternative Solution

An alternative choice is to allow the user to determine whether to let the framekiller work, as discovered by the Framekiller Killer.

var framekiller = true;
window.onbeforeunload = function {
if(framekiller) {
return "..."; // any message that helps user to make decision
}
};

and the code below should be added after the frame tag:

//"my_frame" should be changed according to the real id of the frame in your page
document.getElementById("my_frame").onload = function {
framekiller = false;
};

Limitations

This client-side JavaScript

Client-side JavaScript

Client-side JavaScript is JavaScript that runs on the client-side. While JavaScript was originally created to run this way, the term was coined because the language is no longer limited to just client-side, since server-side JavaScript is now available.-Environment:The most common Internet media...

 solution relies on the end-user's browser enforcing their own security. This makes it a beneficial, but unreliable, means of disallowing your page to be embedded in other pages. The following situations may render the script above useless:

• The user agent does not support JavaScript.
• The user agent supports JavaScript but the user has turned support off.
• The user agent's JavaScript support is flawed or partially implemented.
• The user agent's behavior is modified by a virus or plug-in (possibly without the user's knowledge) in a way that undermines the framekiller script.

In 2010 Gustav Rydstedt, Elie Bursztein

Elie Bursztein

Elie Bursztein is a French security researcher which focus on web, mobile and offensive security . He is most known for his work on CAPTCHA,, his novel attacks and his creative use of applied cryptography...

, Dan Boneh

Dan Boneh

Dan Boneh is a Professor of Computer Science and Electrical Engineering atStanford University. He is a well-known researcher in the areas of applied cryptographyand computer security.-Education:...

and Collin Jackson published a paper that highlighted the limitations of current frame-busting techniques and proposed the following improved version :






DIV frames

A malicious site may also use a <div> element and javascript to "frame" the content. These are not easily amenable to javascript remedies. Such attempts end up incorporating the framed documents headers and tags such as