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Title:      Unchecked Buffer in File Decompression Functions Could
            Lead to Code Execution (Q329048)
Date:       02 October 2002
Software:   Microsoft Windows 98 with Plus! Pack, Windows Me,
            or Windows XP 
Impact:     Two vulnerabilities, the most serious of which could
            run code of attacker?s choice 
Max Risk:   Moderate
Bulletin:   MS02-054

Microsoft encourages customers to review the Security Bulletin at: 
http://www.microsoft.com/technet/security/bulletin/MS02-054.asp.
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Issue:
======
Zipped files (files having a .zip extension) provide a means to 
store information in a way that uses less space on a hard disk. This
is accomplished by compressing the files that are put into in the
zipped file. On Windows 98 with Plus! Pack, Windows Me and Windows
XP, the Compressed Folders feature allows zipped files to be treated
as folders. The Compressed Folders feature can be used to create,
add files to, and extract files from zipped files. 

Two vulnerabilities exist in the Compressed Folders function: 

 - An unchecked buffer exists in the programs that handles the
   decompressing of files from a zipped file. A security
   vulnerability results because attempts to open a file with
   a specially malformed filename contained in a zipped file could
   possibly result in Windows Explorer failing, or in code of the
   attacker?s choice being run. 
 - The decompression function could place a file in a directory
   that was not the same as, or a child of, the target directory
   specified by the user as where the decompressed zip files should
   be placed. This could allow an attacker to put a file in a known
   location on the users system, such as placing a program in a
   startup directory 

Mitigating Factors:
====================
 - The vulnerabilities could not be exploited without user
   intervention. The attacker would need to entice the user to
   receive, store, and open the zipped file provided by the
   attacker. 
 - The vulnerabilities could not be exploited remotely. An attacker
   would need to lure a user into receiving the zipped file onto
   the user?s machine. Best practices suggest users not accept
   e-mail attachments from people who are not trusted, and not to
   download files from untrusted Internet sites. 
 - On Windows 98 and Windows Me, the Compressed Folders feature is
   not installed by default. Users who had not installed this
   feature would not be vulnerable. 

Risk Rating:
============
 - Internet systems: Low
 - Intranet systems: Low
 - Client systems: Moderate

Patch Availability:
===================
 - A patch is available to fix this vulnerability. Please read the 
   Security Bulletin at
   http://www.microsoft.com/technet/security/bulletin/ms02-054.asp
   for information on obtaining this patch.

Acknowledgment:
===============
 - Joe Testa of Rapid7, Inc. (http://www.rapid7.com/) for reporting
   the Unchecked Buffer in Zipped File Handling vulnerability. 
 - zen-parse for reporting the Incorrect Target Path for Zipped
   File Decompression vulnerability.

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