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IBM AIX chcod Local Privilege Escalation Vulnerability
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SUMMARY
The chcod program is "a setuid root application, installed by default
under newer versions of IBM AIX, that manages capacity upgrade on demand
(CUoD)".
Local exploitation of an untrusted path vulnerability in the chcod command
included by default in multiple versions of IBM Corp. AIX could allow for
arbitrary code execution as the root user.
DETAILS
Vulnerable Systems:
* IBM AIX version 5.2
During execution, chcod invokes an external application ("grep") while
trusting the user specified PATH environment variable. Root privileges are
not dropped before this execution occurs, thus allowing an attacker to
gain root access by specifying a controlled path and creating a malicious
binary within that path. All an attacker needs to do to exploit the
vulnerability is create a file called grep which contains malicious code,
set their PATH variable to the current directory, and execute
/usr/sbin/chcod.
Analysis:
The impact of this vulnerability is lessened by the fact that an attacker
must first gain access to the system group in order to use this binary.
Once group id system has been acquired, all that is required to exploit
this vulnerability is a writable directory. This
directory can be the user's home directory, or even the /tmp directory,
provided setuid execution is allowed. Exploitation does not require any
knowledge of application internals, making privilege escalation trivial,
even for unskilled attackers.
Workaround:
Only allow trusted users local access to security critical systems. Only
allow trusted users access to the system group. Alternately, remove the
setuid bit from chcod using chmod u-s /usr/sbin/chcod.
Vendor Response:
"IBM provides the following fixes:
* APAR number for AIX 5.1.0: IY64356 (available)
* APAR number for AIX 5.2.0: IY64355 (available)
* APAR number for AIX 5.3.0: IY64354 (available)
NOTE: Affected customers are urged to upgrade to 5.1.0, 5.2.0 or 5.3.0 at
the latest maintenance level."
CVE Information:
<http://www.cve.mitre.org/cgi-bin/cvename.cgi?name=CAN-2004-1028>
CAN-2004-1028
Disclosure Timeline:
11/02/2004 - Initial vendor notification
11/04/2004 - Initial vendor response
12/20/2004 - Coordinated public disclosure
ADDITIONAL INFORMATION
The information has been provided by
<mailto:idlabs-advisories@idefense.com> iDEFENSE.
The original article can be found at:
<http://www.idefense.com/application/poi/display?id=170&type=vulnerabilities>
http://www.idefense.com/application/poi/display?id=170&type=vulnerabilities
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