iDefense Security Advisory 06.04.08
http://labs.idefense.com/intelligence/vulnerabilities/ 
Jun 04, 2008

I. BACKGROUND

VMware is a software virtualization system which allows multiple virtual
computers to run on a single system. VMware Tools provides drivers and
utilities to enhance and optimize the experience within a guest
operating system running under VMware. For more information visit the
vendor's site at the following URL.

http://www.vmware.com/ 

II. DESCRIPTION

Local exploitation of a input validation vulnerability within VMware's
Hgfs.sys driver could allow an unprivileged attacker to execute
arbitrary code within the kernel of a Windows guest operating system.

When a VMware guest operating system has the VMware Tools package
installed, the hgfs.sys driver is loaded on the machine. This driver
allows any user to open the device "\\.\hgfs" and issue IOCTLs with a
buffering mode of METHOD_NEITHER. This allows untrusted user mode code
to pass kernel addresses as arguments to the driver.

With specially constructed input, a malicious user can use functionality
within the driver to patch kernel addresses and execute arbitrary code
in kernel mode.

III. ANALYSIS

Exploitation of this vulnerability allows an unprivileged local user to
patch and execute arbitrary code within the kernel of a Windows guest
operating system. In order to exploit the vulnerability, an attacker
needs to be able to login to the target VMware guest virtual machine
and execute a specially crafted executable.

IV. DETECTION

iDefense confirmed the existence of this vulnerability in hgfs.sys as
included with VMware Workstation 5.5.4. Other versions are suspected
vulnerable as well.

V. WORKAROUND

Removing VMware Tools from affected guest systems will prevent
exploitation of this issue. However, doing so will also reduce
performance and affect the usability of that virtual machine.

VI. VENDOR RESPONSE

VMware has addressed this vulnerability by releasing new versions of
their affected products. In order to address affected guest operating
systems, VMware Tools must be upgraded within the guest. For more
information, consult VMware's advisory at the following URL.

http://www.vmware.com/security/advisories/VMSA-2008-0009.html 

VII. CVE INFORMATION

The Common Vulnerabilities and Exposures (CVE) project has assigned the
name CVE-2008-5671 to this issue. This is a candidate for inclusion in
the CVE list (http://cve.mitre.org/), which standardizes names for 
security problems.

VIII. DISCLOSURE TIMELINE

09/19/2007  Initial vendor notification
09/19/2007  Initial vendor response
06/04/2008  Coordinated public disclosure

IX. CREDIT

This vulnerability was reported to iDefense by Stephen Fewer of Harmony
Security.

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X. LEGAL NOTICES

Copyright =A9 2008 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
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