bugtraq - ISA Server - Error Page Cross Site Scripting

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Date: Wed, 16 Jul 2003 11:07:42 -0700
From: "Brett Moore" <brett.moore@...urity-assessment.com>
To: "Bugtraq@...urityfocus. Com" <bugtraq@...urityfocus.com>
Subject: ISA Server - Error Page Cross Site Scripting

========================================================================
= ISA Server - Error Page Cross Site Scripting
=
= brett.moore@...urity-assessment.com
= http://www.security-assessment.com
=
= MS Bulletin posted: July 16, 2003
= http ://www.microsoft.com/technet/security/bulletin/MS03-028.asp
=
= Affected Software:
=         Microsoft Internet Security and Acceleration (ISA) Server 2000 
= 	
= Public disclosure on July 16, 2003
========================================================================

This is very similar to the problem resolved by the MS02-18 advisory.
A default error page can be used to conduct cross site scripting attacks
against a legitimate user. While XSS attacks usually involve cookie theft
they can also be used to inject 'fake' login screens that appear to be
hosted on a legitimate site. These login screens can then capture
credentials returning them to a collector script.

== MS03-028 states ==

ISA Server contains a number of HTML-based error pages that allow the
server to respond to a client requesting a Web resource with a customized
error. A cross-site scripting vulnerability exists in many of these error
pages that are returned by ISA Server under specific error conditions.

== MS03-028 ==

== Description ==

The particular request required and the results may depend on the 
configuration of the server. Since many of the error pages are 
vulnerable to this attack, different malformed requests are likely to 
return exploitable results.

When attempting to access a non-existent web page protected by ISA server
without the proper credentials, the browser is returned a 403 error page
with the following abbreviated information.

------------------------------------------------------------------------
  Please try the following
    - Click the refresh button
    - Open the <site> home page, and then look for links

    403 Forbidden - The server denies the specified URL
------------------------------------------------------------------------

The URL of <site> is outputted to the browser without filtering of the
username:password information allowing an attacker to inject scripting
to be executed in the domain of the ISA server.					

== Exploitation ==

This test returned a page that included an iframe, when sent against our
test server.
  *http://[iframe]:test@[site]/test

where [ and ] are replace with angle brackets and [site] is the server.

The exploit example from Thor Larholm for the MS02-18 advisory can also
be applied against a vulnerable ISA installation. This leads to the use 
of a scripting file hosted off-site, allowing for large portions of 
scripting to be included in the attack.

== Solutions ==

- Install the vendor supplied patch.

== Credit ==

Based on work by Thor Larholm at Pivx.com.
  http://www.pivx.com/larholm/adv/TL001/default.htm

Discovered and advised to Microsoft May 21, 2003 by Brett Moore of
Security-Assessment.com

%-) 

== About Security-Assessment.com ==

Security-Assessment.com is a leader in intrusion testing and security
code review, and leads the world with SA-ISO, online ISO17799 compliance
management solution. Security-Assessment.com is committed to security
research and development, and its team have previously identified a
number of vulnerabilities in public and private software vendors products.