Microsoft Security Bulletin MS03-028: Flaw in ISA Server Error Pages Could Allow Cross-Site Scripting Attack (Q816456)

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Title:      Flaw in ISA Server Error Pages Could Allow Cross-Site 
            Scripting Attack (816456)
Date:       16 July 2003
Software:   Microsoft(r) ISA Server        
Max Risk:   Important
Bulletin:   MS03-028

Microsoft encourages customers to review the Security Bulletins         
at: 
http://www.microsoft.com/technet/security/bulletin/MS03-028.asp
http://www.microsoft.com/security/security_bulletins/ms03-028.asp
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Issue:
======

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.

To exploit this flaw, an attacker would have to first be aware of 
a specific ISA server and its access policies or host an ISA 
server of their own and create specific access policies designed 
to exploit this vulnerability. The attacker could then craft a 
request to trigger a page refusal. Once the attack was crafted, 
the attacker would have to host a Web site containing the link, 
or send the link to the user in the form of an HTML e-mail. After 
the user previewed or opened the e-mail, the malicious site could 
be visited automatically without further user interaction. In the 
Web-based attack scenario, an attacker would have no way to force 
a user to visit the Web site. 

Mitigating factors: 
====================

 - The vulnerability could only be exploited if the attacker 
could entice another user into visiting a Web page and clicking a 
link on it, or opening an HTML-based e-mail.
 
 - The request must be one that would cause the ISA server to 
respond with one of several affected error pages. 

 - The vulnerability would not normally enable an attacker to 
gain any privileges on an affected ISA Server computer, breach 
the firewall, or compromise any cached content, unless the user 
is operating on the ISA server itself and is using the Web Proxy 
service to access the Internet. 

Risk Rating:
============
Important

Patch Availability:
===================
 - A patch is available to fix this vulnerability. Please read 
the  Security Bulletins at
   
http://www.microsoft.com/technet/security/bulletin/ms03-028.asp
http://www.microsoft.com/security/security_bulletins/ms03-028.asp
   
   for information on obtaining this patch.


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