[UNIX] IBM AIX chdev Local Format String Vulnerability

From: SecuriTeam (support_at_securiteam.com)
Date: 02/17/05

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Date: 17 Feb 2005 19:29:27 +0200

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      IBM AIX chdev Local Format String Vulnerability
    ------------------------------------------------------------------------

    SUMMARY

    The chdev program is "a setuid root application, installed by default
    under multiple versions of IBM AIX, that facilitates the changing of
    device characteristics". Local exploitation of a format string
    vulnerability in the chdev command included by default in multiple
    versions of IBM Corp.'s AIX operating system could allow for arbitrary
    code execution as the root user.

    DETAILS

    Vulnerable Systems:
     * IBM AIX version 5.2

    The vulnerability specifically exists due to an improperly used formatted
    printing function. When provided with an incorrect argument (argv[1]) that
    contains a format string, the format string will be fed into a formatted
    printing function, and the user supplied format string will be evaluated,
    allowing for a malicious user to examine stack memory and write to
    arbitrary memory locations. With a properly crafted string, this can lead
    to the execution of arbitrary code.

    Analysis:
    This vulnerability can only be exploited by a local user who has been
    granted access to the "system" group. Successful exploitation leads to
    root-level access.

    Due to the nature of the vulnerability, information leakage is trivial and
    aids the attacker in exploitation.

    Workaround:
    Only allow trusted users local access to security critical systems. Only
    allow trusted system administrators access to the "system" group.
    Alternately, remove the setuid bit from chdev using chmod u-s
    /usr/sbin/chdev.

    Vendor response:
    The vendor has not released a patch for this issue, however, the following
    details have been published:
    <http://www-1.ibm.com/support/docview.wss?uid=isg1IY67455>
    http://www-1.ibm.com/support/docview.wss?uid=isg1IY67455

    In addition, a security advisory will be posted at the following site:
    <https://techsupport.services.ibm.com/server/pseries.subscriptionSvcs?mode=1> https://techsupport.services.ibm.com/server/pseries.subscriptionSvcs?mode=1

    Please note that a free signup is required to access the security
    advisory.

    Disclosure Timeline:
    12/21/2004 - Initial vendor notification
    01/07/2005 - Initial vendor response
    02/07/2005 - Coordinated public disclosure

    ADDITIONAL INFORMATION

    The information has been provided by
    <mailto:customerservice@idefense.com> iDEFENSE.
    The original article can be found at:
    <http://www.idefense.com/application/poi/display?type=vulnerabilities>
    http://www.idefense.com/application/poi/display?type=vulnerabilities

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