Microsoft Security Bulletin MS03-009: Flaw In ISA Server DNS Intrusion Detection Filter Can Cause Denial Of Service (331065)

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Title:      Flaw In ISA Server DNS Intrusion Detection Filter Can   
            Cause Denial Of Service (331065)
Date:       19 March 2003
Software:   Microsoft ISA Server 
Impact:     Denial of Service
Max Risk:   Moderate
Bulletin:   MS03-009

Microsoft encourages customers to review the Security Bulletins at: 
http://www.microsoft.com/technet/security/bulletin/MS03-009.asp
http://www.microsoft.com/security/security_bulletins/ms03-009.asp
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Issue:
======
Microsoft Internet Security and Acceleration (ISA) Server 2000 
contains the ability to apply application filters to incoming 
traffic. Application filters allow ISA Server to analyze a data 
stream for a particular application and provide application-
specific processing including inspecting, screening or blocking, 
redirecting, or modifying the data as it passes through the 
firewall. This mechanism is used to protect against invalid URLs 
which may indicate attempted attacks as well as attacks against 
internal Domain Name Service (DNS) Servers.

A flaw exists in the ISA Server DNS intrusion detection application 
filter, and results because the filter does not properly handle a 
specific type of request when scanning incoming DNS requests.

An attacker could exploit the vulnerability by sending a specially 
formed request to an ISA Server computer that is publishing a DNS 
server, which could then result in a denial of service to the 
published DNS server. DNS requests arriving at the ISA Server would 
be stopped at the firewall, and not passed through to the internal 
DNS server. All other ISA Server functionality would be unaffected.

Mitigating Factors:
====================
 - By default, no DNS servers are published. DNS server publishing   
 
   must be manually enabled. 
 - The vulnerability would not enable an attacker to gain any 
   privileges on an affected ISA Server or the published DNS server  
   or to compromise any cached content on the server. It is 
   strictly a denial of service vulnerability. 


Risk Rating:
============
 - Moderate

Patch Availability:
===================
 - A patch is available to fix this vulnerability. Please read the 
   Security Bulletins at

 http://www.microsoft.com/technet/security/bulletin/ms03-009.asp
 http://www.microsoft.com/security/security_bulletins/ms03-009.asp

   for information on obtaining this patch.


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