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IBM AIX chdev Local Format String Vulnerability

02.07.05

BACKGROUND

The chdev program is a setuid root application, installed by default
under multiple versions of IBM AIX, that facilitates the changing of
device characteristics.

DESCRIPTION

Local exploitation of a format string vulnerability in the chdev command
included by default in multiple versions of IBM Corp.'s AIX operating
system could allow for arbitrary code execution as the root user.

The vulnerability specifically exists due to an improperly used
formatted printing function. When provided with an incorrect argument
(argv[1]) that contains a format string, the format string will be fed
into a formatted printing function, and the user supplied format string
will be evaluated, allowing for a malicious user to examine stack memory
and write to arbitrary memory locations. With a properly crafted string,
this can lead to the execution of arbitrary code.

ANALYSIS

This vulnerability can only be exploited by a local user who has been
granted access to the "system" group. Successful exploitation leads to
root-level access.

Due to the nature of the vulnerability, information leakage is trivial
and aids the attacker in exploitation.

DETECTION

iDEFENSE has confirmed the existence of this vulnerability in IBM AIX
version 5.2. It is suspected that previous versions are also vulnerable.

WORKAROUND

Only allow trusted users local access to security critical systems. Only
allow trusted system administrators access to the "system" group.
Alternately, remove the setuid bit from chdev using chmod u-s
/usr/sbin/chdev.

VENDOR RESPONSE

The vendor has not released a patch for this issue, however, the
following details have been published:

http://www-1.ibm.com/support/docview.wss?uid=isg1IY67455

In addition, a security advisory will be posted at the following site:

https://techsupport.services.ibm.com/server/pseries.subscriptionSvcs?mode=1

Please note that a free signup is required to access the security
advisory.

CVE INFORMATION

The Common Vulnerabilities and Exposures (CVE) project has assigned the
names CAN-2005-0240 to these issues. This is a candidate for inclusion
in the CVE list (http://cve.mitre.org), which standardizes names for
security problems.

DISCLOSURE TIMELINE

12/21/2004   Initial vendor notification
01/07/2005   Initial vendor response
02/07/2005   Coordinated public disclosure

CREDIT

iDEFENSE Labs is credited with this discovery.

Get paid for vulnerability research
http://www.idefense.com/poi/teams/vcp.jsp

LEGAL NOTICES

Copyright © 2005 Verisign, 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
part of this alert in any other medium other than electronically, please
email 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.