Public Vulnerability Reports

WinPcap NPF.SYS bpf_filter_init Arbitrary Array Indexing Vulnerability



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.


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.


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.


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 iDefense suspects older versions to also be vulnerable.


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


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


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 (, which standardizes names for security problems.


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


The discoverer of this vulnerability wishes to remain anonymous.

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Copyright © 2007 Verisign, Inc.

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