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Title:      Flaw In Winsock Proxy Service And ISA Firewall Service
	    Can Cause Denial Of Service (331066)
Date:       09 April 2003
Software:   Microsoft Proxy Server 2.0, Microsoft ISA Server
Impact:     denial of service
Max Risk:   Important
Bulletin:   MS03-012

Microsoft encourages customers to review the Security Bulletins
at:

http://www.microsoft.com/technet/security/bulletin/MS03-012.asp
http://www.microsoft.com/security/security_bulletins/ms03-012.asp
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Issue:
======
There is a flaw in the Winsock Proxy service in Microsoft Proxy
Server 2.0, and the Microsoft Firewall service in ISA Server 2000,
that would allow an attacker on the internal network to send a
specially crafted packet that would cause the server to stop
responding to internal and external requests. Receipt of such a
packet would cause CPU utilization on the server to reach 100%, and
thus make the server unresponsive. The Winsock Proxy service and
Microsoft Firewall service work with FTP, telnet, mail, news,
Internet Relay Chat (IRC), or other client applications that are
compatible with Windows Sockets (Winsock). These services allow
these applications to perform as if they were directly connected to
the Internet. These services redirect the necessary communications
functions to a Proxy Server 2.0 or ISA Server computer, thus
establishing a communication path from the internal application to
the Internet through it.

Mitigating Factors:
====================

- - The vulnerability would not enable an attacker to gain any
privileges on an affected Proxy Server 2.0 or ISA Server computer
or compromise any cached content. It is strictly a denial of
service.

- - ISA Server computers running in cache mode are not affected
because the Microsoft Firewall service is disabled by default.


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/ms03-012.asp
http://www.microsoft.com/security/security_bulletins/ms03-12.asp

for information on obtaining this patch.

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