Public Vulnerability Reports

IBM AIX 5.2 crontab BSS Buffer Overflow Vulnerability

10.30.07

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

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.

ANALYSIS

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

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.

WORKAROUND

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

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

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.

DISCLOSURE TIMELINE

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

CREDIT

The discoverer of this vulnerability wishes to remain anonymous.

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LEGAL NOTICES

Copyright © 2007 Verisign, 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.