Trend Micro Antivirus UPX Parsing Kernel Divide by Zero Vulnerability

iDefense Security Advisory 03.14.07
http://labs.idefense.com/intelligence/vulnerabilities/
Mar 14, 2007

I. BACKGROUND

Trend Micro AntiVirus is an virus scanning engine included in a wide array
of products by Trend Micro. Several examples of vulnerable products
include PC-cillin and Internet Security Suite.

http://www.trendmicro.com/en/home/us/home.htm

II. DESCRIPTION

Remote exploitation of a divide by zero error in Trend Micro AntiVirus may
allow attackers to cause a denial of service.

The vulnerability exists in the kernel driver, VsapiNT.sys. This driver is
responsible for scanning various file formats for malicious content. The
code that parses UPX files takes an integer value from an attacker
supplied file and uses it as a divisor. This results in a divide by zero
error in kernel mode. This causes a kernel fault resulting in a blue
screen of death (BSOD).

III. ANALYSIS

Exploitation of this vulnerability results not only in a DOS of the Trend
Micro process, but in an operating system crash.

There are several different attack vectors depending on which product is
being targeted. Someone targeting a home user would need to convince a
user to download a file from a website or an attachment from an email
message. The user would then need to manually scan this file or save it
and have the Trend Micro auto scan process scan it at some later time. If
instead a mail gateway is being targeted this vulnerability can be
exploited automatically by sending a malicious attachment through a
gateway that uses Trend Micro to scan content.

IV. DETECTION

iDefense has confirmed the existence of this vulnerability in Trend Micro
AntiVirus version 14.10.1041, engine version 8.320.1003. Previous versions
may also be affected.

V. WORKAROUND

iDefense is currently unaware of any workarounds for this issue.

VI. VENDOR RESPONSE

"To address this vulnerability, Trend Micro recommends customers to update
to Virus Pattern File 4.335.00 or higher."

For more information, consult the Trend Micro Knowledge Base article at
the link shown below.

http://esupport.trendmicro.com/support/viewxml.do?ContentID=EN-1034587

VII. CVE INFORMATION

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

VIII. DISCLOSURE TIMELINE

02/27/2007  Initial vendor notification
02/27/2007  Initial vendor response
03/14/2007  Coordinated public disclosure

IX. CREDIT

The discoverer of this vulnerability wishes to remain anonymous.

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X. LEGAL NOTICES

Copyright © 2007 iDefense, Inc.

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Disclaimer: The information in the advisory is believed to be accurate at
the time of publishing based on currently available information. Use of
the information constitutes acceptance for use in an AS IS condition.
There are no warranties with regard to this information. Neither the
author nor the publisher accepts any liability for any direct, indirect,
or consequential loss or damage arising from use of, or reliance on, this
information.