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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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