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

           ESB-2002.284 -- Microsoft Security Bulletin MS02-027
         Unchecked Buffer in Gopher Protocol Handler Can Run Code 
                   of Attacker's Choice (Q323889) (2.0)
                               17 June 2002

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

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

Product:                Internet Explorer
                        Proxy Server
                        Internet Security and Acceleration Server
Vendor:                 Microsoft
Operating System:       Windows
Impact:                 Execute Arbitrary Code/Commands
Access Required:        Remote

Ref:                    ESB-2002.277

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Title:      Unchecked Buffer in Gopher Protocol Handler Can Run Code
            of Attacker's Choice (Q323889)
Released:   11 June 2002
Revised:    14 June 2002 (version 2.0)
Software:   Internet Explorer, Proxy Server, Internet Security and
            Acceleration Server
Impact:     Run Code of Attacker's Choice
Max Risk:   Critical
Bulletin:   MS02-027

Microsoft encourages customers to review the Security Bulletin at: 
http://www.microsoft.com/technet/security/bulletin/MS02-027.asp.
- - ----------------------------------------------------------------------

Reason for Revision:
====================
On June 11, 2002, Microsoft released the original version of this
bulletin. In it, we detailed a work-around procedure that customers
 could implement to protect themselves against a publicly disclosed 
vulnerability. An updated version of this bulletin was rereleased
on June 14, 2002 to announce the availability of patches for
Proxy Server 2.0 and ISA Server 2000 and to advise customers that
the work-around procedure is no longer needed on those platforms.
Patches for IE are forthcoming and this bulletin will be
re-released to announce their availability. 

Issue:
======
This is a work-around bulletin that details steps customers can
take to protect themselves against a publicly disclosed
vulnerability until patches are available. 

The Gopher protocol is a legacy protocol that provides for the
transfer of text-based information across the Internet.
Information on Gopher servers is hierarchically presented using a
menu system, and multiple Gopher servers can be linked together to
form a collective "Gopherspace". 

There is an unchecked buffer in a piece of code which handles the
response from Gopher servers. This code is used independently in
IE, ISA, and Proxy Server. A security vulnerability results
because it is possible for an attacker to attempt to exploit this
flaw by mounting a buffer overrun attack through a specially
crafted server response. The attacker could seek to exploit the
vulnerability by crafting a web page that contacted a server
under the attacker's control. The attacker could then either post
this page on a web site or send it as an HTML email. When the page
was displayed and the server's response received and processed,
the attack would be carried out. 

A successful attack requires that the attacker be able to send
information to the intended target using the Gopher protocol.
Anything which inhibited Gopher connectivity could protect against
attempts to exploit this vulnerability. In the case of IE, the
code would be run in the user's context. As a result, any
limitations on the user would apply to the attacker's code
as well. 


Mitigating Factors:
====================
 - A successful attack requires that the attacker's server be
   able to deliver information to the target using the Gopher
   protocol. Customers who block Gopher at the perimeter would be
   protected against attempts to exploit this vulnerability across
   the Internet. 

 - In the case of IE, code would run in the security context of
   the user. As a result, any limitations on the user's ability
   would also restrict the actions an attacker's code could take. 

 - A successful attack against ISA and Proxy servers would
   require that the malicious response be received by the web
   proxy service. In practical terms, this means that a proxy
   client would have to submit the initial request through the
   proxy server.

Risk Rating:
============
 - Internet systems: Critical
 - Intranet systems: Critical
 - Client systems: Critical

Patch Availability:
===================
 - A patch is currently under development to fix this
   vulnerability. Please read the Security Bulletin at
   http://www.microsoft.com/technet/security/bulletin/ms02-027.asp
   for workaround information while patches are developed.

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

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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