Public Vulnerability Reports

IBM AIX libc MALLOCDEBUG File Overwrite Vulnerability



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 website at the following URL.


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.


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


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


iDefense is currently unaware of any workaround for this issue.


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


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


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


The discoverer of this vulnerability wishes to remain anonymous.

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