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iDefense Security Advisory 10.30.07: IBM AIX 5.2 crontab BSS Buffer Overflow Vulnerability
From: iDefense Labs <labs-no-reply () idefense com>
Date: Tue, 30 Oct 2007 14:14:25 -0400

IBM AIX 5.2 crontab BSS Buffer Overflow Vulnerability

iDefense Security Advisory 10.30.07
http://labs.idefense.com/intelligence/vulnerabilities/
Oct 30, 2007

I. BACKGROUND

The crontab program is a user utility that enables users to create,
remove, and edit cron jobs. The cron jobs will then later be executed,
on behalf of the user, at the specified time. Under AIX, the crontab
program is installed by default and is set-uid root. More information
can be found at the URL shown.

http://publib.boulder.ibm.com/infocenter/pseries/v5r3/topic/com.ibm.aix.cmds/doc/aixcmds1/crontab.htm

II. DESCRIPTION

Local exploitation of a buffer overflow vulnerability in the crontab
program of IBM Corp.'s AIX 5.2 operating system allows attackers to
execute arbitrary code with root privileges.

The problem specifically exists within the main function. While
processing command line arguments, the crontab program will copy a
user-supplied argument to a fixed size BSS (data segment) buffer. Since
no bounds checking is performed, it's possible to overwrite a large
portion of the data stored in the BSS memory area.

III. ANALYSIS

Exploitation allows an attacker to execute arbitrary code with root
privileges. Local access is required to execute the crontab program.

IV. DETECTION

iDefense has confirmed the existence of this vulnerability within AIX
version 5.2. Previous versions are suspected to be vulnerable. AIX 5.3
does not appear to be vulnerable.

V. WORKAROUND

Removing the set-uid bit from the crontab program will protect against
exploitation. However, doing so will render the program unusable.

VI. VENDOR RESPONSE

IBM Corp. has addressed this vulnerability by releasing interim fixes.
More information can be found via the Bulletins tab of IBM's
Subscription Service for UNIX and Linux servers. You can reach this
service by clicking the URL shown below.

http://www14.software.ibm.com/webapp/set2/subscriptions/pqvcmjd?mode=1

VII. CVE INFORMATION

The Common Vulnerabilities and Exposures (CVE) project has assigned the
name CVE-2007-4621 to this issue. This is a candidate for inclusion in
the CVE list (http://cve.mitre.org/), which standardizes names for
security problems.

VIII. DISCLOSURE TIMELINE

08/29/2007  Initial vendor notification
09/12/2007  Initial vendor response
10/30/2007  Coordinated public disclosure

IX. CREDIT

The discoverer of this vulnerability wishes to remain anonymous.

Get paid for vulnerability research
http://labs.idefense.com/methodology/vulnerability/vcp.php

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http://labs.idefense.com/

X. LEGAL NOTICES

Copyright © 2007 iDefense, 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 e-mail 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.


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