Public Vulnerability Reports

Apple Mac OS X AppleTalk ASP Message Kernel Heap Overflow Vulnerability

11.14.07

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

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.

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.

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 

WORKAROUND

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

 # appletalk -d 

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

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.

DISCLOSURE TIMELINE

08/08/2007 Initial vendor notification
08/09/2007 Initial vendor response
11/14/2007 Public disclosure

CREDIT

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

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LEGAL NOTICES

Copyright © 2007 Verisign, 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 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.