bugtraq - Re: Hotmail Cross Site Scripting Vulnerability

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Message-ID: <004001c46c1b$bfbb0c80$060010b0@dagon>
Date: Sat, 17 Jul 2004 18:33:10 +0200
From: "GreyMagic Security" <security@...ymagic.com>
To: "Paul" <paul@...yhats.cjb.net>, <bugtraq@...urityfocus.com>
Subject: Re: Hotmail Cross Site Scripting Vulnerability

>Hotmail Cross Site Scripting Vulnerability

--snip--

>Well, Hotmail was just nice enough to be a little lenient on what
>goes in-between those 'if' tags. I suppose that's so MS Word can
>send stuff through email to Hotmail customers without it getting
>messed up.

The problem is not "if" tags, the problem is the syntax in which they are
represented in the document (HTML Comments). Hotmail doesn't check anything
between HTML comments because it assumes they won't be processed by the
browser, not because it tries to leave backdoors for MSO docs. Hotmail's
assumption that HTML comments are safe collides with the well-documented
concept of "conditional comments" by the very same company.

See
http://msdn.microsoft.com/workshop/author/dhtml/overview/ccomment_ovw.asp
for more information.

Btw, this will work just fine without any need for MSO trickery:

<!--[if IE gte 5]> <img src="javascript:alert()"> <![endif]-->

Simply checks if IE's major version is equal or greater than 5 and executes
the content if true (older versions don't have the conditional comments
feature, but they're irrelevant market-share wise anyway).

Cheers.