IBM AIX bellmail Stack Buffer Overflow Vulnerability
iDefense Security Advisory 10.30.07
Oct 30, 2007
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.
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.
Exploitation allows an attacker to execute arbitrary code with root
privileges. Local access is required to execute and interact with the
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.
iDefense has confirmed the existence of this vulnerability within AIX
version 5.3 (5300-06) and 5.2. Previous versions are suspected to be
Removing the set-uid bit from the bellmail 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.
VII. 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
VIII. DISCLOSURE TIMELINE
08/28/2007 Initial vendor notification
08/28/2007 Initial vendor response
10/30/2007 Coordinated public disclosure
This vulnerability was discovered by Joshua J. Drake of VeriSign
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Copyright =A9 2007 iDefense, Inc.
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