iDefense Security Advisory 11.14.07
http://labs.idefense.com/intelligence/vulnerabilities/
Nov 14, 2007

I. BACKGROUND

AppleTalk, a set of networking protocols developed by Apple, was
originally implemented on early Mac operating systems. Although it is a
legacy protocol, it is still supported on the latest version of Mac OS
X. AppleTalk is compiled into the default kernel, but must be turned on
in order to be used. More information can be found at the following URL.

http://docs.info.apple.com/article.html?artnum=50039

II. DESCRIPTION

Local exploitation of a stack based buffer overflow in Apple Inc.'s OS X
may allow an attacker to execute arbitrary code in kernel context.

The vulnerability exists within the function responsible for adding an
AppleTalk zone to an interface's routing table. A zone can be thought
of as something similar to a Windows Domain.

When copying the user provided zone information into a fixed size stack
buffer, the kernel uses a user provided length as the number of bytes
to copy into the destination buffer. This results in an exploitable
stack buffer overflow in the kernel.

III. ANALYSIS

Successful exploitation of this vulnerability will result in the
execution of arbitrary code in kernel context. Unsuccessful attempts
will likely crash the system.

In order to exploit this vulnerability, the system needs to have
AppleTalk configured in routing mode. This is not enabled by default.
It would likely be enabled on a Mac system running on a network with
legacy Mac hosts.

IV. DETECTION

iDefense has confirmed the existence of this vulnerability in Mac OS X
10.4.10, Workstation and Server editions. Previous versions may also be
affected.

To determine if AppleTalk is running, the following command can be
executed on the command line.

  $ appletalk -s

V. WORKAROUND

Disabling AppleTalk will prevent exploitation of this vulnerability.
Executing the following command will disable AppleTalk if it is
enabled.

  # appletalk -d

VI. VENDOR RESPONSE

Apple addressed this vulnerability within their Mac OS X 2007-008
security update. More information is available at the following URL.

http://docs.info.apple.com/article.html?artnum=307041

VII. CVE INFORMATION

The Common Vulnerabilities and Exposures (CVE) project has assigned the
name CVE-2007-4267 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

08/08/2007  Initial vendor notification
08/09/2007  Initial vendor response
11/14/2007  Coordinated public disclosure

IX. CREDIT

The discoverer of this vulnerability wishes to remain anonymous.

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X. LEGAL NOTICES

Copyright © 2007 iDefense, Inc.

Permission is granted for the redistribution of this alert
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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.

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