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JavaScript Injection

Summary: JavaScript injection is a nifty little technique that allows you to alter a sites contents without actually leaving the site. This can be very useful when say, you need to spoof the server by editing some form options. Examples will be explained throughout.

Contents:

  • I. Injection Basics
  • II. Cookie Editing
  • III. Form Editing

I. Injection Basics

JavaScript injections are run from the URL bar of the page you are visiting. To use them, you must first completely empty the URL from the URL bar. That means no http:// or whatever.

JavaScript is run from the URL bar by using the JavaScript: protocol. In this tutorial I will only teach you the bare bones of using this, but if you are a JavaScript guru, you can expand on this using plain old JavaScript.

The two commands covered in this tutorial are the alert(); and void(); commands. These are pretty much all you will need in most situations. For your first JavaScript injection, you will make a simple window appear, first go to any website and then type the following into your URL bar:

Code:

javascript:alert('Hello, World');

You should get a dialog box that says "Hello, World". This will be altered later to have more practical uses.

You can also have more than one command run at the same time.

Code:

javascript:alert('Hello'); alert('World');

This would pop up a box that said 'Hello' and than another that says 'World'.

II. Cookie Editing

First off, check to see if the site you are visiting has set any cookies by using this script.

Code:

javascript:alert(document.cookie);

This will pop up any information stored in the sites cookies. To edit any information, we make use of the void(); command.

Code:

javascript:void(document.cookie = "Field = myValue");

This command can either alter existing information or create entirely new values. Replace "Field" with either an existing field found using the alert(document.cookie); command, or insert your very own value. Then replace "myValue" with whatever you want the field to be. For example.

Code:

javascript:void(document.cookie = "Authorized=yes");

Would either make the field "authorized" or edit it to say "yes"... now whether or not this does anything of value depends on the site you are injecting it on.

It is also useful to tack an alert(document.cookie); at the end of the same line to see what effect your altering had.

III. Form Editing

Sometimes, to edit values sent to a given website through a form, you can simply download that html and edit it slightly to allow you to submit what you want. However, sometimes the website checks to see if you actually submitted it from the website you were supposed to. To get around this, we can just edit the form straight from JavaScript. Note: The changes are only temporary, so it's no use trying to deface a site through JavaScript injection like this.

Every form on a given webpage (unless named otherwise) is stored in the forms[x] array... where "x" is the number, in order from top to bottom, of all the forms in a page. Note that the forms start at 0, so the first form on the page would actually be 0, and the second would be 1 and so on. Lets take this example.

Code:

<form action="http://www.website.com/submit.php" method="post">
<input type="hidden" name="to" value="admin@website.com">

Note: Since this is the first form on the page, it is forms[0]

Say this form was used to email vital server information to the admin of the website. You can't just download the script and edit it because the submit.php page looks for a referer. You can check to see what value a certain form element has by using this script.

Code:

javascript:alert(document.forms[0].to.value);

This is similar to the alert(document.cookie); discussed previously. In this case, It would pop up an alert that says "admin@website.com"

So here's how to Inject your email into it. You can use pretty much the same technique as the cookies editing shown earlier.

Code:

javascript:void(document.forms[0].to.value = "email@nhacks.com");

This would change the email of the form to be "email@nhacks.com". Then you could use the alert(); script shown above to check your work. Or you can couple both of these commands on one line. Submitting this form would now email the new injected email address.


Tutorial by Raduce


Comments

Reply

thanks RaducE thats a decent tutorial, I thought you\'d forget to mention that form[0] is the first form on the page, form[1] is the second but you didnt :)

Reply

FireBug is better :P

Reply

fire bug works? i couldn't get it

Reply

im not getting any descriptions of cookies, no alert boxes, just nothing. wats the deal. everything is blank in url except the javascript

Reply

let me guess, you are using firefox?

Reply

Lol i found this out myself...you cant use advanced javascript commands in firefox's address bar BUT, if you type them into a bookmark (as the location) it works :D

Reply

It's nice to use javascript as a inline debugger. Some major browser like firefox and chrome may not allow to use javascript:expression as url. But they have inspect element option. You can get more comfort with it. Additionally you can use firebug in chrome and firefox.

Reply

Thanks ReducE good tutorial easy to understand. especially for someone like me who is just starting out nice1

Reply

Edit ANY site:

javascript:document.body.contentEditable%20=%20'true';%20document.designMode='on';%20void%200

Reply

Edit ANY site:

javascript:document.body.contentEditable%20=%20'true';%20document.designMode='on';%20void%200

Reply

<script>alert("Fuck Me!")<script>;

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