AUSCERT External Security Bulletin Redistribution
                  ESB-2000.184 -- CERT Advisory CA-2000-14
                    Microsoft Outlook and Outlook Express
                         Cache Bypass Vulnerability
                                27 July 2000


	AusCERT Security Bulletin Summary

Product:		Outlook Express 4.0 to 5.01
			Outlook 97
			Outlook 98
			Outlook 2000
Vendor:			Microsoft
Operating System:	MS Windows
Platform:		N/A

Impact:			Read and Create Arbitrary files
Access Required:	Remote

Ref:			ESB-2000.181

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CERT Advisory CA-2000-14 Microsoft Outlook and Outlook Express Cache Bypass

   Original release date: July 26, 2000
   Source: CERT/CC
   A complete revision history is at the end of this file.
Systems Affected

     * Any system running Microsoft Outlook Express 4.0 or 4.01
     * Any system running Microsoft Outlook Express 5.0 or 5.01
     * Any system running Microsoft Outlook 98
     * Any system running Microsoft Outlook 2000

   Microsoft has recently released Microsoft Security Bulletin MS00-046,
   in which they announced a patch for the "Cache Bypass" vulnerability.
   By exploiting this vulnerability, an attacker can use an
   HTML-formatted message to read certain types of files on the victim's
   In addition, because this vulnerability also allows the attacker to
   store files on the victim's machine, it can be used in conjunction
   with existing vulnerabilities to execute arbitrary code on the target
I. Description

"Cache Bypass" Vulnerability

   Typically, all files downloaded by either Outlook or Internet Explorer
   are stored in an area known as a cache. The cache serves two main
   purposes. First, it provides temporary storage for online content,
   which minimizes the amount of data that must be transferred when
   refreshing a page. Second, it provides an area where Internet content
   can be downloaded to the local machine and accessed with the same
   security policy as remote content.
   This vulnerability allows attackers to use an HTML-formatted message
   to store files outside the cache. Inside the cache, the files are
   governed by the security policy of the "Internet Zone," but outside
   they are governed by the "Local Computer Zone." Once a file is stored
   in the "Local Computer Zone," the security policy of the "Internet
   Zone" no longer applies to it. This could put systems at risk because
   the security policies of the "Local Computer Zone" are typically more
   permissive than those of the "Internet Zone."
II. Impact

   When exploited, this vulnerability allows an attacker to store an HTML
   file in an area that is not protected by the policies of the "Internet
   Zone." This file may then be used to open arbitrary files on the
   victim's machine and send their contents back to the attacker.
   In addition, the "Cache Bypass" vulnerability could be used in
   conjunction with other vulnerabilities to allow an intruder to execute
   arbitrary code on the victim's machine.
III. Solution

   Microsoft has released Microsoft Security Bulletin MS00-046, which
   points to a patch for this vulnerability. We strongly encourage you to
   read this bulletin and apply the patch. MS00-046 is available at
   The CERT Coordination Center would like to thank Microsoft for its
   assistance in developing this advisory.
   Author: Jeffrey P. Lanza
   This document is available from:
CERT/CC Contact Information

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          Phone: +1 412-268-7090 (24-hour hotline)
          Fax: +1 412-268-6989
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   Copyright 2000 Carnegie Mellon University
   Revision History
July 26, 2000:  Initial release

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