IBM AIX auditselect Local Format String Vulnerability

02.08.05

BACKGROUND

The auditselect program is a setuid root application, installed by
default under multiple versions of IBM AIX, that selects audit records
for analysis according to defined criteria.

DESCRIPTION

Local exploitation of a format string vulnerability in the auditselect
command included by default in multiple versions of IBM Corp.'s AIX
operating system could allow for arbitrary code execution as the root
user.

The vulnerability specifically exists due to an improperly used
formatted printing function. When provided with an incorrect argument
(argv[1]) that contains a format string, the format string will be fed
into a formatted printing function, and the user supplied format string
will be evaluated, allowing for a malicious user to examine stack memory
and write to arbitrary memory locations. With a properly crafted string,
this can lead to the execution of arbitrary code.

ANALYSIS

This vulnerability can only be exploited by a local user who has been
granted access to the "audit" group. Successful exploitation leads to
root-level access.

Due to the nature of the vulnerability, information leakage is trivial
and aids the attacker in exploitation.

DETECTION

iDEFENSE has confirmed the existence of this vulnerability in IBM AIX
version 5.2. It is suspected that previous versions are also vulnerable.
IBM has reported that AIX 5.3 is also vulnerable.

WORKAROUND

Only allow trusted users local access to security critical systems. Only
allow trusted system administrators access to the "audit" group.
Alternately, remove the setuid bit from auditselect using chmod u-s
/usr/sbin/auditselect.

VENDOR RESPONSE

The following details have been published:

http://www-1.ibm.com/support/docview.wss?uid=isg1IY67519

"IBM provides the following fixes:

      APAR number for AIX 5.1.0: IY67802 (available approx. 03/23/05)
      APAR number for AIX 5.2.0: IY67472 (available approx. 04/15/05)
      APAR number for AIX 5.3.0: IY67519 (available approx. 04/15/05)

NOTE: Affected customers are urged to upgrade to 5.1.0, 5.2.0 or 5.3.0
at the latest maintenance level."

CVE INFORMATION

The Common Vulnerabilities and Exposures (CVE) project has assigned the
names CAN-2005-0250 to these issues. This is a candidate for inclusion
in the CVE list (http://cve.mitre.org), which standardizes names for
security problems.

DISCLOSURE TIMELINE

12/21/2004   Initial vendor notification
01/07/2005   Initial vendor response
02/08/2005   Public disclosure

CREDIT

iDEFENSE Labs is credited with this discovery.

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