[UNIX] IBM AIX chcod Local Privilege Escalation Vulnerability

From: SecuriTeam (support_at_securiteam.com)
Date: 12/21/04

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Date: 21 Dec 2004 13:02:47 +0200

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      IBM AIX chcod Local Privilege Escalation Vulnerability
    ------------------------------------------------------------------------

    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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