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             __________________________________________________________

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

                             INFORMATION BULLETIN

                   SGI IRIX startmidi/stopmidi Vulnerability

February 13, 1997 00:00 GMT                                        Number H-28
______________________________________________________________________________
PROBLEM:       A vulnerability exists in the startmidi(1)/stopmidi(1) program. 
PLATFORM:      All SGI systems running IRIX 5.2, 5.3, 6.0, 6.0.1, and 6.1
               with an IRIS Digital Media Execution Environment. 
DAMAGE:        This vulnerability may allow local users to gain root 
               privileges or perform a denial of service attack. 
SOLUTION:      Until patches are available, take the steps outlined in section 
               3 as soon as possible. 
______________________________________________________________________________
VULNERABILITY  Exploit details involving this vulnerability have been made 
ASSESSMENT:    publicly available. 
______________________________________________________________________________

[ Start AUSCERT Advisory ]

===========================================================================
AA-97.05                        AUSCERT Advisory
                   SGI IRIX startmidi/stopmidi Vulnerability
                                11 February 1997

Last Revised: --

- ----------------------------------------------------------------------------

AUSCERT has received information that a vulnerability exists in the
startmidi(1)/stopmidi(1) program which is part of the SGI IRIS Digital
Media Execution Environment.

This vulnerability may allow local users to gain root privileges or
perform a denial of service attack.

Exploit information 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

    The SGI IRIS Digital Media Execution Environment contains the basic
    system components necessary to support audio, MIDI (Musical Instrument
    Digital Interface), and video applications on an IRIS workstation.
    One part of this product is the MIDI Execution Environment, which
    among other things, contains the startmidi/stopmidi program.  stopmidi
    is a symbolic link to the startmidi program.

    Before any MIDI applications can be run, it is usually necessary to
    configure the serial ports for use with MIDI.  startmidi initializes
    the serial ports and links them to the MIDI streams driver. stopmidi
    disables MIDI on the specified device.

    During the execution of startmidi, files are created in an insecure
    manner with insecure permissions.  As this program executes with root
    privileges, it is possible for local users to create or truncate
    arbitrary files on the system.  It also possible to alter the contents
    of these temporary files, which may allow users to perform a denial
    of service attack.

    Exploit information has been made publicly available.

    The default location for startmidi/stopmidi is /usr/sbin/.

    At this stage, IRIX 5.2, 5.3, 6.0, 6.0.1, and 6.1 are known to contain
    this vulnerability.  Sites can determine the version of the operating
    system with the command:

  % 
/sbin/uname -a

2.  Impact

    Local users may be able to create or truncate arbitrary files on
    the system, which may be leveraged to gain root access.  They may
    also be able to change the contents of temporary files, allowing a
    denial of service attack.

3.  Workarounds/Solution

    AUSCERT recommends that sites prevent the exploitation of this
    vulnerability in startmidi/stopmidi by immediately applying the
    workaround given in Section 3.1.  If the MIDI Execution Environment
    is not required, it is recommended that sites remove it from their
    systems (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 execute permissions

    Until official vendor patches are made available, sites should remove
    the setuid root and execute permissions from startmidi.  To do this,
    the following command should be run as root:

        # /bin/chmod 400 /usr/sbin/startmidi
        # /bin/ls -l /usr/sbin/startmidi
        -r--------   1 root   sys   18608 Nov 22  1994 /usr/sbin/startmidi

    Note that this will remove the ability for any user to run the
    startmidi or stopmidi program.  If only the setuid permissions are
    removed, it is still possible for users to gain privileges when
    startmidi is executed by the root user.

3.2 Remove the MIDI Execution Environment

    If the  MIDI Execution Environment is no longer needed, sites are
    encouraged to remove it completely from their systems.  This can be
    done by running, as root, the GUI software management tool, swmgr, or
    the command:

        # /usr/sbin/versions remove dmedia_eoe.sw.midi

    Sites can check that the package has been removed with the command:
        
        # /usr/sbin/versions dmedia_eoe.sw.midi

4.  Additional measures

    Most Unix systems ship with numerous programs which have setuid or
    setgid privileges.  Often the functionality supplied by these
    privileged programs is not required by many sites.  The large number
    of privileged programs that are shipped by default are to cater for
    all possible uses of the system.

    AUSCERT encourages sites to examine all the setuid/setgid programs
    and determine the necessity of each program.  If a program does not
    absolutely require the setuid/setgid privileges to operate (for
    example, it is only run by the root user),  the setuid/setgid
    privileges should be removed.  Furthermore, if a program is not
    required at your site, then all execute permissions should be removed.

    A sample command to find all setuid/setgid programs is (run as root):

       # find / \( -perm -4000 -o -perm -2000 \) -exec ls -ld {} \;

    It is AUSCERT's experience that many vulnerability are being
    discovered in setuid/setgid programs which are not necessary for the
    correct operation of most systems.  Sites can increase their security
    by removing unnecessary setuid/setgid programs.

    For example, the functionality provided by the startmidi/stopmidi
    program is not needed by most sites.  If sites had previously disabled
    this program, they would not have been susceptible to this latest
    vulnerability.

===========================================================================
[ End AUSCERT Advisory ]

_______________________________________________________________________________

CIAC wishes to acknowledge the contributions of AUSCERT and Silicon Graphics for 
the information contained in this bulletin.
_______________________________________________________________________________


CIAC, the Computer Incident Advisory Capability, is the computer
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