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.

ASP, as its name implies, is a Session Layer protocol that is used by
the AppleTalk File Sharing protocol to establish connections with a
peer. More information can be found at the following URL.

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

II. DESCRIPTION

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

The vulnerability exists within a function responsible for sending an
ASP (AppleTalk Session Protocol) message on an AppleTalk socket. When
allocating a buffer, the kernel uses a user provided integer to perform
an arithmetic operation that calculates the number of bytes to allocate.
This calculation can overflow, leading to the allocation of a buffer of
insufficient size. This results in an exploitable heap based buffer
overflow within the kernel.

III. ANALYSIS

Successful exploitation of this vulnerability will result in the
execution of arbitrary code in kernel context. Exploitation has proven
to be non-trivial.

In order to reach the vulnerable code, a system would have to have
AppleTalk turned on. It would likely be used on a network consisting of
older Mac hosts since previous versions of Mac relied on it to implement
Apple File Sharing.

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-2007-4269 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  Public disclosure

IX. CREDIT

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

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http://labs.idefense.com/methodology/vulnerability/vcp.php 

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X. LEGAL NOTICES

Copyright =A9 2007 iDefense, Inc.

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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
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