iDefense Security Advisory 12.17.07
http://labs.idefense.com/intelligence/vulnerabilities/
Dec 17, 2007

I. BACKGROUND

The mount_smbfs utility is used to mount a remote SMB share locally. It
is installed set-uid root, so as to allow unprivileged users to mount
shares, and is present in a default installation on both the Server and
Desktop versions of Mac OS X. For more information visit the following
URL.

http://developer.apple.com/documentation/Darwin/Reference/ManPages/man8/mount_smbfs.8.html

II. DESCRIPTION

Local exploitation of a stack based buffer overflow vulnerability in
Apple Inc.'s Mac OS X mount_smbfs utility could allow an attacker to
execute arbitrary code with root privileges.

The vulnerability exists in a portion of code responsible for parsing
command line arguments. When processing the -W option, which is used to
specify a workgroup name, the option's argument is copied into a fixed
sized stack buffer without any checks on its length. This leads to a
trivially exploitable stack based buffer overflow.

III. ANALYSIS

Exploitation of this vulnerability results in the execution of arbitrary
code with root privileges. In order to exploit this vulnerability, an
attacker must have execute permission for the set-uid root mount_smbfs
binary.

IV. DETECTION

iDefense has confirmed the existence of this vulnerability in Mac OS X
version 10.4.10, on both the Server and Desktop versions. Previous
versions may also be affected.

V. WORKAROUND

Removing the set-uid bit from the mount_smbfs binary will prevent
exploitation. However, non-root users will be unable to use the
program.

VI. VENDOR RESPONSE

Apple addressed this vulnerability within their Mac OS X 2007-009
security update. More information is available at the following URL.

http://docs.info.apple.com/article.html?artnum=307179

VII. CVE INFORMATION

The Common Vulnerabilities and Exposures (CVE) project has assigned the
name CVE-2007-3876 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

07/16/2007  Initial vendor notification
07/17/2007  Initial vendor response
12/17/2007  Coordinated public disclosure

IX. CREDIT

This vulnerability was discovered by Sean Larsson of VeriSign iDefense
Labs.

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 customerservice@idefense.com 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.