Public Vulnerability Reports

IBM AIX at Information Disclosure Vulnerability

02.10.09

BACKGROUND

'at' is a Unix command used to schedule commands to run at a later time. For more information, see the vendor's site found at the following link.

http://publib16.boulder.ibm.com/doc_link/EN_US/a_doc_lib/cmds/aixcmds1/at.htm

DESCRIPTION

Local exploitation of an information disclosure vulnerability in IBM Corp.'s Advanced Interactive eXecutive (AIX) could allow an attacker to read arbitrary files on the file system.

IBM's AIX is a Unix operating system based on System V, which runs on the PowerPC (PPC) architecture.

The at command suffers from a race condition, which allows attackers to read arbitrary files on the file system. When the at command processes the "-f" command line switch, it fails to access the supplied file name in a proper manner. This allows for symbolic link attacks to occur.

ANALYSIS

Exploitation of this issue allows an attacker to view arbitrary files, which could contain potentially sensitive information. An attacker would need to create a program which runs the at command with the "-f" command switch. The program would also need to conduct the symbolic link attack, which would cause the file name supplied to point to an arbitrary file the attacker wished to read. In a typical scenario, the attacker would read the password file. This would give the attacker access to the password hashes used for authentication. The attacker could then crack these hashes offline and elevate privileges, if successful.

DETECTION

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

WORKAROUND

Removing the setuid bit from the at binary will provide a workaround for this issue. This will make the program unusable.

VENDOR RESPONSE

IBM has released a patch which addresses this issue. Information about vendor updates can be found by clicking on the URLs shown.

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

CVE INFORMATION

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

DISCLOSURE TIMELINE

12/16/2008 - Requested PoC
01/06/2009 - PoC Sent
02/10/2009 - Public Disclosure

CREDIT

The discoverer of this vulnerability wishes to remain anonymous.

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