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.
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
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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.
