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WinPcap NPF.SYS bpf_filter_init Arbitrary Array Indexing Vulnerability

11.12.07

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/

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.

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.

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.

WORKAROUND

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

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

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.

DISCLOSURE TIMELINE

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

CREDIT

The discoverer of this vulnerability wishes to remain anonymous.

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LEGAL NOTICES

Copyright © 2007 Verisign, Inc.

Permission is granted for the redistribution of this alert electronically. It may not be edited in any way without the express written consent of iDefense. If you wish to reprint the whole or any part of this alert in any other medium other than electronically, please e-mail customer service for permission.

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.