Yahoo, Hotmail Open to Attack

Again, or still, security flaws open your online mail accounts to exploits.

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The vulnerability was discovered in an Internet Explorer feature used to process extensions to HTML called HTML + TIME. The security hole could allow attackers to steal log-in and password information, or browse the contents of an e-mail account, according to an advisory released by GreyMagic Software.

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The company tested the vulnerability against Yahoo and Hotmail, but it could affect other e-mail services, GreyMagic said.

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Hotmail and Yahoo filter incoming HTML-format e-mail messages for malicious code. However, the filtering, combined with support for HTML + TIME, makes it possible to inject malicious script into incoming e-mail messages, GreyMagic said

They are using a flaw in IE, but I am wondering if other browsers could be exploited in the same way.
SOURSE

hehe, now whenever somebody asks how to hack Hotmail, to go read the news. That is why I never send anything important via email.

Yep, from my email group

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GreyMagic Security Advisory GM#005-MC
=====================================

By GreyMagic Software, Israel.
23 Mar 2004.

Topic: Remotely Exploitable Cross-Site Scripting in Hotmail and Yahoo.

Discovery date: 06 Mar 2004.

Affected applications:
======================

* Hotmail web-based email service (when used with IE).
* Yahoo web-based email service (when used with IE).

Note that many other web-based services may be vulnerable to this method of
exploitation, as it is a completely new way to embed script.

Introduction:
=============

Both Hotmail and Yahoo make tremendous efforts to sanitize incoming emails
from potentially unsafe HTML content. Flawed filtering of such unsafe
content may result in severe consequences that would occur as soon as a user
opens an email for reading, including:

* Theft of login and password.
* Content disclosure of any email in the mailbox.
* Automatically send emails from the mailbox.
* Exploitation of known vulnerabilities in the browser to access the user's
file system and eventually take over the machine.
* Distribution of a web-based email worm.
* Disclosure of all contacts within the address book.

Discussion:
===========

GreyMagic devised a method to inject such arbitrary (potentially malicious)
content to a Yahoo or Hotmail email message. The method is not limited to
Hotmail and Yahoo alone though, it may apply to other web-based services
that attempt to filter HTML input.

The vulnerability makes use of an Internet Explorer technology called
HTML+TIME (based on SMIL), which is meant to add timing and media
synchronization support to HTML pages.

One of the features included in HTML+TIME is the ability to manipulate any
attribute on an element via special control elements. For example, the
<t:set> element exposes the attributes "attributeName" and "to", which make
it possible to inject ANY HTML content to the document when "attributeName"
is set to "innerHTML" and "to" is set to any HTML the attacker would like to
execute, including script.

Exploit:
========

For the HTML+TIME module to be activated, the document must fulfill two
requirements. It must declare the designated namespace and it must bind the
namespace to the HTML+TIME behavior implementation.

In order to fulfill the first requirement it is usually necessary to be able
to access the <html> element, with the syntax <html
xmlns:t="urn:schemas-microsoft-com:time">. However, Hotmail completely
filters out that element, so another method of namespace declaration is
needed. It so happens that Internet Explorer provides one other mechanism to
declare a namespace, via the non-standard <?xml:namespace> processing
instruction, which may be used anywhere in the document and does not get
filtered.

The second requirement usually involves the use of the CSS "behavior"
property, with the syntax "behavior:url(#default#time)". However, Hotmail
blocks all instances of "url(...)" in the incoming mail, so another way to
bind the behavior must be used. It comes in the form of the <?import>
element, which was added in Internet Explorer 5.5 and enables namespace to
implementation binding.

So after evading all filters, the final code looks like this:

<?xml:namespace prefix="t" ns="urn:schemas-microsoft-com:time" />
<?import namespace="t" implementation="#default#time2">
Optional text here...
<div>
<t:set attributeName="innerHTML" to="<script
defer>alert()</script>A" />
</div>

Demonstration:
==============

We put together a proof of concept demonstration, which can be found at
Removed for security reasons

Solution:
=========

GreyMagic started work on this issue with Microsoft on 11-Mar-2004. They
have quickly confirmed our findings and were able to produce a fix less than
two days later. As a result, Hotmail is no longer vulnerable to this method
of exploitation.

All attempts to contact Yahoo unfortunately failed. Mail was sent to
security and secure at yahoo.com and at yahoo-inc.com, no replies were
received to date.

Tested on:
==========

Hotmail.
Yahoo.

Disclaimer:
===========

The information in this advisory and any of its demonstrations is provided
"as is" without warranty of any kind.

GreyMagic Software is not liable for any direct or indirect damages caused
as a result of using the information or demonstrations provided in any part
of this advisory.

- Copyright © 2004 GreyMagic Software.

Hey Hey,

I think that this is a very important post, not for the information about the exploit, but for the information that comes behind it. Microsoft responded and solved the problem in Hotmail is less than 48 hours.

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Source: xmaddness/VulnWatch
GreyMagic started work on this issue with Microsoft on 11-Mar-2004. They have quickly confirmed our findings and were able to produce a fix less than two days later. As a result, Hotmail is no longer vulnerable to this method of exploitation.

Where as Yahoo has still not fixed the problem, nor have they even commented on the subject

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Source: http://story.news.yahoo.com/news?tmp...pcworld/115323
However, Yahoo users and other users of Web-based e-mail services could be vulnerable to attack via the security hole, GreyMagic said.

Yahoo could not be reached for comment.

I think this proves a point about Microsoft at least taking people seriously and listening to it. They fixed the problem fairly quickly.

Peace,
HT