iDefense Security Advisory 10.30.07: IBM AIX 5.2 crontab BSS Buffer Overflow Vulnerability

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.

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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.

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. Received on Tue Oct 30 14:46:25 2007