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SunOS "chkey" security vulnerability

The attached CIAC advisory describes a security problem in the Solaris
"chkey" command.  This problem allows users already having accounts, to
gain root access.

We've patched most of the vulnerable hosts, using a patch supplied by
sun.

[This notice is a part of OAC's efforts to keep the campus informed of
potential computer security liabilities.  Please send any questions or
concerns to us at DCS@UCI.EDU]

             __________________________________________________________

                       The U.S. Department of Energy
                    Computer Incident Advisory Capability
                           ___  __ __    _     ___
                          /       |     /_\   /
                          \___  __|__  /   \  \___
             __________________________________________________________

                             INFORMATION BULLETIN

May 22, 1997 17:00 GMT                                             Number H-59
===========================================================================
AA-97.18                        AUSCERT Advisory
                 Solaris 2.x chkey Buffer Overflow Vulnerability
                                  22 May 1997

Last Revised:

-
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AUSCERT has received information that a vulnerability exists in the
chkey(1) program under Solaris 2.x.

This vulnerability may allow local users to gain root privileges.

Exploit information involving this vulnerability has been made publicly
available.

Currently there are no vendor patches available that address this
vulnerability.  AUSCERT recommends that sites take the steps outlined in
section 3 as soon as possible.

This advisory will be updated as more information becomes available.
-
-----------------------------------------------------------------------------

1.  Description

    AUSCERT has received information that a vulnerability exists in the
    Solaris 2.x chkey(1) program.

    chkey is used to change a user's secure RPC public key and secret key
    pair.

    Due to insufficient bounds checking on arguments passed to the chkey
    program, it is possible to overwrite the internal data space of this
    program while it is executing. As chkey has setuid root permissions,
    this vulnerability may allow local users to gain root privileges.

    Exploit information involving this vulnerability has been made publicly
    available.

    chkey under Solaris 2.x is located by default in /usr/bin/.

    Sun Microsystems is aware of this problem and is currently
    investigating it.

2.  Impact

    Local users may gain root privileges.

3.  Workarounds/Solution

    AUSCERT recommends that sites limit the possible exploitation of this
    vulnerability by immediately applying the workaround given in Section
    3.1.

    To maintain the functionality of chkey, AUSCERT recommends applying
    the workaround given in Section 3.2.

    Currently there are no vendor patches available that address this
    vulnerability.  AUSCERT recommends that official vendor patches be
    installed when they are made available.

3.1 Remove setuid and non-root execute permissions

    To prevent the exploitation of the vulnerability described in this
    advisory, AUSCERT recommends that the setuid permissions be removed
    from the chkey program immediately.  As the chkey program will no
    longer work for non-root users, it is recommended that the execute
    permissions for them also be removed.

        # ls -l /usr/bin/chkey
        -r-sr-xr-x   1 root   sys      19608 Oct 25  1995 /usr/bin/chkey

        # chmod 500 /usr/bin/chkey

        # ls -l /usr/bin/chkey
        -r-x------   1 root   sys      19608 Oct 25  1995 /usr/bin/chkey

    For those sites which require the chkey functionality, AUSCERT
    recommends applying the workaround given in Section 3.2.

3.2 Install wrapper

    AUSCERT has developed a wrapper to help prevent programs from being
    exploited using the vulnerability described in this advisory.  Sites
    which have a C compiler can obtain the source, compile and install
    the wrapper as described in Section 3.2.1. For sites without a C
    compiler, AUSCERT has made pre-compiled binaries available for Solaris
    2.4, 2.5 and 2.5.1 (Section 3.2.2).

3.2.1 Installing the wrapper from source

    The source for the wrapper, including installation instructions, can
    be obtained from:

        ftp://ftp.auscert.org.au/pub/auscert/tools/overflow_wrapper/
                                                overflow_wrapper.c

    This wrapper replaces the chkey program and checks the length of the
    command line arguments which are passed to it.  If an argument exceeds
    a certain predefined value (MAXARGLEN), the wrapper exits without
    executing the chkey command.  The wrapper program can also be
    configured to syslog any failed attempts to execute chkey with
    arguments exceeding MAXARGLEN.  For further instructions on using this
    wrapper, please read the comments at the top of overflow_wrapper.c.

    When compiling overflow_wrapper.c for use with chkey, AUSCERT recommends
    defining MAXARGLEN to be 32.

    The MD5 checksum for the current version of overflow_wrapper.c can be
    retrieved from:

        ftp://ftp.auscert.org.au/pub/auscert/tools/overflow_wrapper/CHECKSUM

    The CHECKSUM file has been digitally signed using the AUSCERT PGP key.

3.2.2 Installing the wrapper binaries

    Pre-compiled wrapper binaries are provided for sites that wish to
    install the wrapper but do not have a C compiler available.  AUSCERT
    has compiled the wrapper on Solaris 2.4, 2.5 and 2.5.1.  The following
    compile time options have been used to the create the binaries:

         REAL_PROG='"/usr/bin/chkey.real"'
         MAXARGLEN=32
         SYSLOG

    More information on these options can be found in Section 3.2.1 and
    in the overflow_wrapper.c source code.

    The pre-compiled binaries for the wrapper program can be retrieved
    from:


ftp://ftp.auscert.org.au/pub/auscert/tools/AA-97.18-chkey_wrapper.tar.Z

    The MD5 checksum for AA-97.18-chkey_wrapper.tar.Z is:

        MD5 (AA-97.18-chkey_wrapper.tar.Z) = bafd43c2357156595d65c7ed38fd6aeb

    AA-97.18-chkey_wrapper.tar.Z contains a README file with installation
    instructions, as well as pre-compiled binaries for /usr/bin/chkey
    under Solaris 2.4, 2.5 and 2.5.1. The binaries have been linked
    statically so they are larger than the default chkey binary.

    Sites are encouraged to carefully read the installation notes in the
    README file before installation.

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