Yahoo! Mail XSS Vulnerability

["Cheng Peng Su" <applesoup@xxxxxxxxx>]

Adivisory Name : Yahoo! Mail XSS Vulnerability
Release Date : 2006.04.21
Application : Yahoo! web-based email service
Test On : Microsoft IE 6.0
Discover : Cheng Peng Su(applesoup_at_gmail.com)

Description:

Yahoo! Mail is one of the Internet's most popular web based email solutions.

Details:

This vulnerability is resulted from the failure of Yahoo! Mail's
filtering engine to

block "expression()" syntax in a CSS attribute using a comment to
break up expression,

and the comment symbol( /* */ ) must be hex encoded so that we can
bypass the filter.

An example:

<SPAN STYLE="width:ex/* good *&#x2F;pression(alert());">Hello</SPAN>

the injected code inside the CSS attribute is responsible for

-Getting cookies.
-Potential web-based e-mail worm.

Vender status:

2006.04.01 Informed the vendor.
2006.04.03 The vendor confirmed the vulnerability.
2006.04.XX The vendor patched the vulnerability. ( They patched it silently )

Original advisory:

http://applesoup.googlepages.com/yahoo_mail_xss.txt