iDefense Security Advisory 11.12.07
http://labs.idefense.com/intelligence/vulnerabilities/ 
Nov 12, 2007

I. BACKGROUND

WinPcap is a software package that facilitates real-time link-level
network access for Windows-based operating systems. A wide range of
open-source projects, including Wireshark, use it. More information is
available at the project's web site at the following URL.

http://www.winpcap.org/ 

II. DESCRIPTION

Local exploitation of an invalid array indexing vulnerability in the
NPF.SYS device driver of WinPcap allows attackers to execute arbitrary
code in kernel context.

The problem specifically exists within the bpf_filter_init function. In
several places throughout this function, values supplied from a
potential attacker are used as array indexes without proper bounds
checking. By making IOCTL requests with specially chosen values,
attackers are able to corrupt the stack, or pool memory, within the
kernel.

III. ANALYSIS

Exploitation allows attackers to execute arbitrary code in kernel
context.

The vulnerable device driver is loaded when WinPcap is initialized. This
driver can be set to load on start-up depending on a choice made at
installation time. However, this is not the default setting.

Normally, the device driver is not loaded until an administrator
utilizes a WinPcap dependent application. Once they do, it will become
accessible to normal users as well. When a program using this driver
exits, it is not unloaded. Attackers will continue to have access until
the driver is manually unloaded.

If the option to allow normal user access was chosen at installation
time, attackers will always have access to this device driver.
Consequently, a local attacker without administrator privileges would
have access to sniff, as well as exploit this vulnerability.

IV. DETECTION

iDefense has confirmed the existence of this vulnerability in version
4.0.1 of WinPcap as included in Wireshark 0.99.6a. The version of
NPF.SYS tested was 4.0.0.901. iDefense suspects older versions to also
be vulnerable.

V. WORKAROUND

iDefense is currently unaware of any effective workaround for this
issue.

VI. VENDOR RESPONSE

The WinPcap Team has addressed this vulnerability by releasing version
4.0.2 of the WinPcap software. For more information, see the following
URL.

http://www.winpcap.org/misc/changelog.htm 

VII. CVE INFORMATION

The Common Vulnerabilities and Exposures (CVE) project has assigned the
name CVE-2007-5756 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

10/30/2007  Initial vendor notification
10/30/2007  Initial vendor response
11/12/2007  Coordinated public disclosure

IX. CREDIT

The discoverer of this vulnerability wishes to remain anonymous.

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X. LEGAL NOTICES

Copyright =A9 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.