Yet another Hotmail security hole - injecting JavaScript in IE using "@import url(javascript:...)"

[joro () NAT BG (Georgi Guninski)]

Georgi Guninski security advisory #3, 2000

Yet another Hotmail security hole - injecting JavaScript in IE using
"@import url(javascript:...)"

Disclaimer:
The opinions expressed in this advisory and program are my own and not
of any company.
The usual standard disclaimer applies, especially the fact that Georgi
Guninski is not liable for any damages caused by direct or  indirect use
of the information or functionality provided by this program.
Georgi Guninski, bears NO responsibility for content or misuse of this
program or any derivatives thereof.

Description:
Hotmail allows executing JavaScript code in email messages using
"@import url(javascript:...)",
which may compromise user's Hotmail mailbox when viewed with Internet
Explorer.

Details:
There is a security flaw in Hotmail which allows injecting and executing
JavaScript code in an email message using the javascript protocol.
This exploit works on Internet Explorer.
Hotmail filters the "javascript:" protocol for security reasons.
But the following JavaScript is executed: "@import url(javascript:...)".

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 it is also possible to
read user's messages, to send messages from user's name and doing other
mischief.
It is also possible to get the cookie from Hotmail, which is dangerous.
Hotmail deliberately escapes all JavaScript (it can escape) to prevent
such attacks, but obviously there are holes.

Workaround: Disable Active Scripting

The code that must be included in HTML email message is:
--------------------------------------------------------
<style TYPE="text/css">
@import url(javascript:alert('Javascript is executed'));
</style>
--------------------------------------------------------

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