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IBM AIX libc MALLOCDEBUG File Overwrite Vulnerability

20.05.09

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 a file overwrite vulnerability in IBM Corp.'s Advanced Interactive eXecutive (AIX) could allow an attacker to overwrite arbitrary files and execute arbitrary code.

The AIX libc implementation of malloc includes a debugging mechanism that is initiated by setting the MALLOCTYPE and MALLOCDEBUG environment variables. This debugging feature writes to a user-specified log file under certain conditions. There is a gap in time between the checks to see if the file is a symbolic link and the process of opening the file. If an attacker can change the file to be a symbolic link to another file within this time frame, it is possible to cause a set-uid binary to write to files owned by privileged users.

ANALYSIS

Exploitation of this issue allows an attacker to overwrite arbitrary files and execute arbitrary code as root.

DETECTION

iDefense 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 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

01/05/2008 - PoC Requested
12/16/2008 - Initial Response
12/16/2008 - Initial notification
01/06/2009 - PoC Sent
05/19/2009 - Coordinated public Disclosure

CREDIT

The discoverer of this vulnerability wishes to remain anonymous.

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