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===========================================================================
             AUSCERT External Security Bulletin Redistribution

           ESB-2001.154 -- Microsoft Security Bulletin MS01-021
               Invalid Web Request Can Cause Access Violation 
                       in ISA Server Web Proxy Service
                               17 April 2001

===========================================================================

        AusCERT Security Bulletin Summary
        ---------------------------------

Product:                ISA Server Web Proxy service
Vendor:                 Microsoft
Impact:                 Denial of Service
Access Required:        Remote

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- - ----------------------------------------------------------------------
Title:      Invalid Web Request Can Cause Access Violation in ISA 
            Server Web Proxy Service
Date:       16 April 2001
Software:   ISA Server 2000
Impact:     Denial of service
Bulletin:   MS01-021

Microsoft encourages customers to review the Security Bulletin 
at: http://www.microsoft.com/technet/security/bulletin/MS01-021.asp.
- - ----------------------------------------------------------------------

Issue:
======
The ISA Server Web Proxy service does not correctly handle web 
requests that contain a particular type of malformed argument. 
Processing such a request would result in an access violation, 
which would cause the Web Proxy service to fail. This would disrupt 
all ingoing and outgoing web proxy requests until the service was 
restarted. 

Mitigating Factors:
====================
 - The vulnerability could be exploited from the Internet only 
   if the Web Publishing feature were enabled. By default, 
   this feature is disabled. 
 - The vulnerability would not enable an attacker to breach the 
   security of the firewall - that is, it would not enable the 
   attacker to access protected resources or bypass the firewall. 
   It would only enable the attacker to deny legitimate service 
   to other users. 
 - The vulnerability would only allow the Web Proxy service to 
   be disrupted. Other ISA services would continue functioning 
   normally. 

Patch Availability:
===================
 - A patch is available to fix this vulnerability. Please read 
   Security Bulletin
   http://www.microsoft.com/technet/security/bulletin/ms01-021.asp
   for information on obtaining this patch.

Acknowledgment:
===============
 - Dr. Richard Reiner, Graham Wiseman, Matthew Siemens, and 
   Kent Nicolson of FSC Internet Corp. / SecureXpert Labs 
  (http://www.fscinternet.com / http://www.securexpert.com) 

- - ---------------------------------------------------------------------

THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS PROVIDED 
"AS IS" WITHOUT WARRANTY OF ANY KIND. MICROSOFT DISCLAIMS ALL 
WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF 
MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT
SHALL 
MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR ANY DAMAGES 
WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL, CONSEQUENTIAL,
LOSS 
OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF MICROSOFT CORPORATION
OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH
DAMAGES. 
SOME STATES DO NOT ALLOW THE EXCLUSION OR LIMITATION OF LIABILITY FOR
CONSEQUENTIAL OR INCIDENTAL DAMAGES SO THE FOREGOING LIMITATION MAY
NOT 
APPLY.



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