SEC Consult SA-20051202-1 :: GMX Webmail XSS



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SEC-CONSULT Security Advisory 20051202-0 GMX / MSIE XSS
==========================================================

Product: GMX Webmail V ?.? in combination with MSIE (maybe other browsers)
Remarks: no other Versions tested but very likely vulnerable

Vulnerablities: Multiple XSS/Relogin-trojan

Vendor: gmx.net
Vendor-Status: first time vendor contacted (2005.12.02)
Vendor-Patchs: ---

Object: MSIE (unknown version - 5.*+)

Exploitable:
Local: ---
Remote: YES
Type: XSS - Cross Site Scripting

============
Introduction
============

GMX-Webmail Vulnerability #1/2005

=====================
Vulnerability Details
=====================


1) XSS / Relogin Trojan
=======================

gmx.net s blacklists fail to detect script-tags in combination with
SPECIAL/META-Characters.
This leavas Webmail users using MSIE vulnerable to typical XSS /
Relogin-trojan attacks.

Vulnerable TAG/ATTRIBUTTE
=========================

P/STYLE (most likely others)

Malicious HTML-Mail:
===================================================================================================================
P-TAG / STYLE ATTRIBUTE:

---cut here---
<html><body>
<p
style="background-image:url(jav[Special/Meta-Chars]ascript:[malicious/script/relogin-trojan...])">Hola
Seniores ...</p>
</body></html>
---cut here---
===================================================================================================================

Remark:

Since the authentication tokens are stored in a second subdomain it is
not possible steal them with a single
XSS. It is very likely that a second XSS vulnerability within this
domain could be used to achieve this goal.
When users want to view HTML messages they have to confirm this by
clicking on a single link. We assume that
everybody would do so.

===============
General remarks
===============

We would like to apologize in advance for potential nonconformities
and/or known issues.

======================================
Recommended hotfixes for webmail-users
======================================

Do not use MS Internet-Explorer.

=================
Recommended fixes
=================

Do not use blacklists on tags and attributes. Whitelist
special/meta-characters.

==============
Vendor-Patches
==============

---

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Contact
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SEC-CONSULT
Austria / EUROPE
research@xxxxxxxxxxxxxxx



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