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IBM AIX libC _LIB_INIT_DBG Arbitrary File Creation Vulnerability

08.04.09

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

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.

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.

DETECTION

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

WORKAROUND

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

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

CVE INFORMATION

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

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

CREDIT

This vulnerability was reported to iDefense by Karol Wiesek.

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