Web Based E-mail (Hotmail Yahoo Gmail) Hack/Hacking with JavaScript

pleez, pleez, PLEEZ teach me how to hack a Hotmail Account!!!”
-unidentified IRC user

From here on in you walk alone. Neither little_v OR Black Sun Research Facility AND its members will be responsible for what you do with the information presented here. Do not use this information to impress your “l33t0_b0rit0″ friends. Do not operate in shower. Objects in article may be closer than they appear.

Note: If you see (x), where x is a number, it means that this term is defined at (x) at the bottom of this article.

Intro

The purpose of this article is NOT, I repeat, NOT to teach someone how to “hack an email account”. It’s true purpose is actually MUCH more devious. The purpose of this and all other articles in the “An Exploit Explained: ” series is to teach readers about various web technologies, and the basics of security and exploiting. I will try to give you a hands-on, learn as you go type of education in computer security. Sound good??? Then let’s get in to it!!

Preface

On Wednesday, Sept. 22 1999, yet another bleary day in the life of little v, the following message was sent to my inbox:

To: BugTraq
Subject: Yet another major Hotmail security hole -
injecting JavaScript using "javasCript:"
Date: Wed Sep 22 1999 10:48:04
Author: Georgi Guninski
Message-ID: <37e8d004.ef848f34@nat.bg>

Yet another major Hotmail security hole - injecting
JavaScript using "javasCript:"

There is a major security flaw in Hotmail which allows
injecting and executing JavaScript code in an email
message using the javascript protocol. This exploit
works both on Internet Explorer 5.0 (guess IE 4.x)
and Netscape Communicator 4.x. Hotmail filters the
"javascript:" protocol for security reasons. But it
does not filter properly the following case:
"javasCript:" where "C" is the ASCII code of "C".

So the following HTML is executed 
if the user has enabled automatically loading of
images (most users have).

Probably this may be used in other HTML tags.

Executing JavaScript when the user opens Hotmail
email message allows for example displaying a fake
login screen where the user enters his password
which is then stolen. I don't want to make a scary
demonstration, but I am sure it is also possible to
read user's messages, to send messages from user's
name and doing other mischief. Hotmail deliberately
escapes all JavaScript (it can escape) to prevent such
attacks, but obviously there are holes. It is much
easier to exploit this vulnerability if the user uses
Internet Explorer 5.0. AFAIK this is not a browser
problem, it is Hotmail's problem.

Workaround: Disable JavaScript

The code is:


....

....
Regards,
Georgi Guninski
http://www.securityfocus.com/external/http://www.nat.bg/~joro

Ok, don’t puke, I’m going to explain what just happened in a fashion that even your dog can understand.

What is this all about?

This important part of this posting to the Bugtraq(1) (http://www.securityfocus.com) mailing list is the actual exploit(2).
The exploit would be:

What does it do?

As this exploit, when put into an email message sent to a hotmail user, opens a little box using the “alert()”(3) function in javascript(4), and is also supposed to read who the first message in your inbox is from. However, this code does not work on its own. You see, the email also says that you need to use the ASCII(5) code for “C” in the message. If I get out my handy HTML reference book, I can see that the ASCII code is C. If we substitute this into our little exploit, minus the “read who the first message in your inbox” part, we get this:

How does it work?

Finding out how an exploit works is always the part that makes people a bit spindizzy. If we look at that gibberish we call code one more time we can see that it uses an tag, which all you who took my HTML tutorial would know is to display an image onto the page. Because hotmail tries to be the “top dog” webmail provider, they allow you to set autoloading of images, so the image just shows up on the same page as the mail. When you open a new hotmail account, this option is already set (hurray!). The conflict happens because your normal browser allows you to put javascript tags into your IMG tags. Because JavaScript is a strong little language, and allows just about full control over someone’s browser, if the conditions are right. Naturally, people like you and me started exploiting hotmail’s allowing of javascript. Soon, the