Public Vulnerability Reports

Apple Mac OS X mount_smbfs Stack Based Buffer Overflow Vulnerability

12.17.07

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

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.

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.

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.

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.

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

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.

DISCLOSURE TIMELINE

07/16/2007 Initial vendor notification
07/17/2007 Initial vendor response
12/17/2007 Coordinated 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.