I. BACKGROUND

The Novell Client software provides a workstation with access to Novell NetWare networks as well as Novell Open Enterprise Server (OES) services. Novell Clients can access the full range of Novell services such as authentication via Novell eDirectory, network browsing and service resolution, and secure and reliable file system access. More information about the Novel Client can be found on the vendor's site at the following URL.

http://www.novell.com/products/clients/

II. DESCRIPTION

Local exploitation of an input validation error vulnerability within Novell NetWare Client could allow an unprivileged attacker to execute arbitrary code within the kernel.

When the Novell NetWare Client is installed on a Windows based operating system, the driver nwfilter.sys will be loaded at system startup. This driver allows any user to open the device "\.\nwfilter" and issue IOCTLs with a buffering mode of METHOD_NEITHER.

The problem specifically exists because the driver 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 within kernel mode.

III. ANALYSIS

Exploitation of this vulnerability allows an unprivileged local user to patch and execute arbitrary code within the kernel. In order to exploit the vulnerability, an attacker needs to be able to log in to the target machine and execute a specially crafted executable.

IV. DETECTION

iDefense has confirmed the existence of this vulnerability in nwfilter.sys, file version 4.91.1.1, as included with Novell's NetWare Client 4.91 SP4. Other versions are suspected vulnerable as well.

V. WORKAROUND

iDefense is currently unaware of any workaround for this issue.

VI. VENDOR RESPONSE

Novell has addressed this vulnerability by releasing patches that remove the "nwfilter.sys" driver. For more information, consult Novell's advisory at the following URL.

https://secure-support.novell.com/KanisaPlatform/Publishing/98/3260263
_f.SAL_Public.html

VII. CVE INFORMATION

The Common Vulnerabilities and Exposures (CVE) project has assigned the name CVE-2007-5667 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

09/25/2007 Initial vendor notification
09/25/2007 Initial vendor response
11/12/2007 Coordinated public disclosure

IX. CREDIT

This vulnerability was reported to iDefense by Stephen Fewer of Harmony Security (www.harmonysecurity.com).

Get paid for vulnerability research
http://labs.idefense.com/methodology/vulnerability/vcp.php

Free tools, research and upcoming events
http://labs.idefense.com/

X. LEGAL NOTICES

Copyright © 2007 iDefense, 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.