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.
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X. LEGAL NOTICES
Copyright © 2007 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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