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             AUSCERT External Security Bulletin Redistribution

           ESB-2004.0173 -- iDEFENSE Security Advisory 02.27.04a
             WinZip MIME Parsing Buffer Overflow Vulnerability
                               01 March 2004

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

Product:                WinZip 9.0 beta
                        WinZip 8.1 SR-1
Publisher:              iDEFENSE
Operating System:       Windows
Impact:                 Execute Arbitrary Code/Commands
Access Required:        Remote

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WinZip MIME Parsing Buffer Overflow Vulnerability

iDEFENSE Security Advisory 02.27.04a:
http://www.idefense.com/application/poi/display?id=76&type=vulnerabilities
February 27, 2004

I. BACKGROUND

WinZip is an archiving utility for the Microsoft Windows platform
featuring built-in support for CAB files and for popular Internet file
formats such as TAR, gzip, UUencode, BinHex, and MIME. ARJ, LZH, and ARC
files are supported via external programs. More information is available
at http://www.winzip.com.

II. DESCRIPTION

Exploitation of a buffer overflow vulnerability within a parameter
parsing routine of WinZip Computing Inc.'s WinZip Archive Utility for
Windows allows remote attackers to execute arbitrary code.

The problem specifically exists in the UUDeview package which is used to
support various decoding routines. When providing long strings to
certain parameters of MIME archives (.mim, .uue, .uu, .b64, .bhx, .hqx
and .xxe extensions) WinZip will crash referencing an "internal error in
file misc.c line 132". Analysis of the log file created by WinZip upon
crash reveals that exploitation is plausible:

    Return address = 0041a923
    Return address = 0044c06c
    Return address = 41414141

Further analysis reveals that WinZip is crashing due to an invalid
reference at the following instruction:

    0049c332: mov dword ptr [ecx+08], edi

Both the ecx and edi registers in the above instruction are user
controllable allowing an attacker to craft a MIME archive that upon
opening will execute arbitrary code.

III. ANALYSIS

Successful exploitation requires that an attacker convince a target user
to open a malicious MIME archive. The target user must have a vulnerable
version of WinZip installed which by default includes a handler for the
one of the vulnerable file types. Example methods of propagation include
e-mail, web links and P2P software.

iDEFENSE has proof of concept exploit code demonstrating the impact of
this vulnerability.

IV. DETECTION

iDEFENSE has confirmed the existence of this vulnerability in WinZip
8.1 SR-1 (the latest stable version) and the latest beta release of
WinZip 9.0. It is suspected that earlier versions are vulnerable as
well.

V. WORKAROUND

User awareness is the best method of defense against this class of
attack. Users must be wary when opening attachments or following links
from untrusted sources.

Removal of the extension handler for vulnerable file types can prevent
exploitation from double clicking on what may appear to be a harmless
WinZip archive. This can be accomplished by opening Windows Explorer,
selecting "Tools", then "Folder Options", selecting the "File Types"
tab, scrolling to MIM and deleting the appropriate entry.

VI. VENDOR FIX

This issue has been addressed in WinZip 9.0, available at
http://www.winzip.com/.

VII. CVE INFORMATION

A Mitre Corp. Common Vulnerabilities and Exposures (CVE) number has not
yet been assigned.

VIII. DISCLOSURE TIMELINE

January 13, 2004        Vulnerability acquired by iDEFENSE
February 9, 2004        Initial vendor notification
February 9, 2004        Initial vendor response
February 10, 2004       iDEFENSE clients notified
February 27, 2004       Coordinated public disclosure

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