[Full-disclosure] iDefense Security Advisory 10.07.09: IBM AIX rpc.cmsd Stack Buffer Overflow Vulnerability

[iDefense Labs <labs-no-reply@xxxxxxxxxxxx>]

iDefense Security Advisory 10.07.09
http://labs.idefense.com/intelligence/vulnerabilities/
Oct 07, 2009

I. BACKGROUND

IBM's AIX is a Unix operating system based on System V, which runs on
the PowerPC (PPC) architecture. For more information, visit the product
web site at the following URL.

http://www.ibm.com/systems/power/software/aix/index.html

II. DESCRIPTION

Remote exploitation of a stack based buffer overflow vulnerability in
IBM Corp.'s AIX could allow an attacker to execute arbitrary code with
the privileges of the affected service.

rpc.cmsd, more commonly known as the Calendar Manager Service Daemon, is
an RPC application used to manage schedules and calendars. It operates
over SUN RPC.

The vulnerability is triggered when handling a request for remote
procedure 21. This function takes two arguments, both of which are XDR
strings. When copying the first argument into a stack based buffer, the
code does not properly verify its length. This results in a stack based
buffer overflow vulnerability.

III. ANALYSIS

Exploitation of this vulnerability results in the execution of arbitrary
code with the privileges of the affected service, usually root. In order
to exploit this vulnerability, an attacker only needs the ability to
connect to the target host via RPC. No authentication is required.

Since the vulnerability is a stack based buffer overflow, exploitation
is relatively trivial.

IV. DETECTION

iDefense has confirmed the existence of this vulnerability in AIX
versions 5.3 and 5.2. IBM reports that this vulnerability is present in
the following products:

AIX 5.3, 6.1, and earlier releases
VIOS 1.4, 1.5, 2.1, and earlier releases

V. WORKAROUND

Disabling the cmsd RPC service via inetd.conf will prevent the
exploitation of this vulnerability. This can be performed using the
'chsubserver' command, and is documented in the AIX advisory linked to
below. However, this will prevent users from using the
Calendar/Scheduler service.

VI. VENDOR RESPONSE

IBM has addressed this issue with an update. Further details and patches
can be found at the following URLs.

http://aix.software.ibm.com/aix/efixes/security/cmsd_advisory.asc
http://aix.software.ibm.com/aix/efixes/security/cmsd_fix.tar

VII. CVE INFORMATION

A Mitre Corp. Common Vulnerabilities and Exposures (CVE) number has not
been assigned yet.

VIII. DISCLOSURE TIMELINE

08/25/2009  Initial vendor notification
08/25/2009  Initial vendor response
10/07/2009  Public disclosure

IX. CREDIT

This vulnerability was reported to iDefense by Rodrigo Rubira Branco
(BSDaemon).

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X. LEGAL NOTICES

Copyright © 2009 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
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.

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