Public Vulnerability Reports

IBM AIX bellmail Stack Buffer Overflow Vulnerability

10.30.07

BACKGROUND

bellmail is a mail user-agent (MUA) and is commonly used for accessing locally stored electronic mail messages. Under AIX, the bellmail 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.commadmn/doc/commadmndita/mail_bellmail.htm

DESCRIPTION

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

The problem specifically exists within sendrmt function. This function is called when a user tries to send mail using the "m" command. Within this function, several sprintf calls are made to concatenate user-supplied input with static strings. No bounds checking is performed to ensure that the resulting string will fit in the destination buffer located on the stack. By supplying a long parameter, an attacker is able to overwrite program control data located on the stack and take control of the affected process.

ANALYSIS

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

It should be noted that the bellmail program does initially set its user (both saved and effective) to that of the calling user. Generally, it would be sufficient to drop these privileges. However, in this case, the bellmail program uses the AIX-specific setpriv functionality to retain the ability chown arbitrary files on the system.

DETECTION

iDefense has confirmed the existence of this vulnerability within AIX version 5.3 (5300-06) and 5.2. Previous versions are suspected to be vulnerable.

WORKAROUND

Removing the set-uid bit from the bellmail 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-2007-4623 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

08/28/2007 Initial vendor notification
08/28/2007 Initial vendor response
10/30/2007 Coordinated public disclosure

CREDIT

This vulnerability was discovered by Joshua J. Drake of VeriSign iDefense Labs.

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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.