iDefense Security Advisory 08.06.09: IBM AIX libC _LIB_INIT_DBG Arbitrary File Creation Vulnerability

[iDefense Labs <labs-no-reply@xxxxxxxxxxxx>]

iDefense Security Advisory 08.04.09
http://labs.idefense.com/intelligence/vulnerabilities/
Aug 04, 2009

I. BACKGROUND

IBM's AIX is a Unix operating system based on System V, which runs on
the PowerPC (PPC) architecture. For more information, visit the product
web site at the following URL.

http://www.ibm.com/systems/power/software/aix/index.html

II. DESCRIPTION

Local exploitation of an arbitrary file creation vulnerability in IBM
Corp.'s Advanced Interactive eXecutive (AIX) Operating System allows
attackers to execute arbitrary code with super-user privileges.

This vulnerability exists due to the handling of several environment
variables. The libC.a library will open files as specified by the
"_LIB_INIT_DBG" and "_LIB_INIT_DBG_FILE" variables. The attacker's
"umask" will be honored, allowing them to create world-writable files,
owned by root, in arbitrary locations on the system.

III. ANALYSIS

Exploitation of this vulnerability allows attackers to execute arbitrary
code with super-user privileges. In order to exploit this vulnerability
an attacker must be able to execute a set-uid binary linked with the
"libC.a" library. In default installations, several binaries may be
executed by any user with a local account; no special group membership
is needed.

IV. DETECTION

iDefense has confirmed the existence of this vulnerability in IBM
Corp.'s AIX version 5.3. Other versions may also be affected.

V. WORKAROUND

iDefense is currently unaware of any effective workaround for this
issue.

VI. VENDOR RESPONSE

IBM has released a patch which addresses this issue. For more
information, consult their advisory at the following URL:

http://aix.software.ibm.com/aix/efixes/security/libC_advisory.asc

VII. CVE INFORMATION

A Mitre Corp. Common Vulnerabilities and Exposures (CVE) number has not
been assigned yet.

VIII. DISCLOSURE TIMELINE

02/25/2009  - Initial Contact
03/03/2009  - Initial Response
08/04/2009  - IBM proposed release date of August 4th, 2009
08/04/2009  - Coordinated public disclosure

IX. CREDIT

This vulnerability was reported to iDefense by Karol Wiesek.

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X. LEGAL NOTICES

Copyright © 2009 iDefense, Inc.

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at the time of publishing based on currently available information. Use
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