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IBM AIX rpc.cmsd Stack Buffer Overflow Vulnerability

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

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.

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.

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

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.

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

CVE INFORMATION

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

DISCLOSURE TIMELINE

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

CREDIT

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

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LEGAL NOTICES

Copyright © 2009 Verisign, Inc.

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