AusCERT - AA-97.21 -- SGI IRIX eject Buffer Overrun Vulnerability

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AA-97.21 -- SGI IRIX eject Buffer Overrun Vulnerability
Date: 17 December 1997

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===========================================================================
AA-97.21                        AUSCERT Advisory
                   SGI IRIX eject Buffer Overrun Vulnerability
                                 27 May 1997

Last Revised: 17 December 1997

              Changed Section 3 to include vendor patch and bulletin
              information.

	      A complete revision history is at the end of this file.

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

AUSCERT has received information that a vulnerability exists in eject(1),
distributed under IRIX versions 5.x and 6.x.  Other versions may also be
vulnerable.

This vulnerability may allow local users to gain root privileges.

Exploit information involving this vulnerability has been made publicly
available.

Vendor patches have been released addressing 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

    eject(1) is a program used to eject a removable media device, such as
    floppy, CDROM, or tape. If the floppy or CDROM is mounted, eject will
    first try to unmount it.

    Due to insufficient bounds checking on arguments which are supplied
    by users, it is possible to overwrite the internal stack space of the
    eject program while it is executing.  By supplying a carefully designed
    argument to the eject program, intruders may be able to force eject
    to execute arbitrary commands.  As eject is setuid root, this may
    allow intruders to run arbitrary commands with root privileges.

    Sites can determine if this program is installed by using:

	% ls -l /usr/sbin/eject

    eject is installed by default in /usr/sbin.  Sites are encouraged to
    check for the presence of this program regardless of the version of
    IRIX installed.

    Specific versions of IRIX which are vulnerable to this problem are
    listed in Section 3.3.

    Exploit information involving this vulnerability has been made publicly
    available.

2.  Impact

    Local users may gain root privileges.

3.  Workarounds/Solution

    Official vendor patches have been released by Silicon Graphics which
    address this vulnerability (Section 3.3).

    If the patches recommended by Silicon Graphics cannot be applied,
    AUSCERT recommends that sites prevent the exploitation of this
    vulnerability by immediately applying the workaround given in Section
    3.1.  If the eject functionality is required by non-root users and
    patches can not be installed, AUSCERT recommends applying the
    workaround given in Section 3.2.

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 eject program immediately.  As eject will no longer have its
    full functionality for non-root users, it is recommended that the
    execute permissions be also removed for these users.

	# ls -l /usr/sbin/eject
	-rwsr-xr-x   1 root    sys    45892 Nov 28 15:09 /usr/sbin/eject

	# chmod 500 /usr/sbin/eject
	# ls -l /usr/sbin/eject
	-r-x------   1 root    sys    45892 Nov 28 15:09 /usr/sbin/eject

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.

    The source for the wrapper, including installation instructions, can
    be found at:

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

    This wrapper replaces the eject 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 eject command.  The wrapper program can also be
    configured to syslog any failed attempts to execute eject 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 eject, 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.

3.3 Install vendor patches

    Silicon Graphics has released a security bulletin containing
    information on this vulnerability including patch details. The original
    release of this bulletin can be retrieved from:

        ftp://sgigate.sgi.com/security/19970507-02-PX

    Information on patches which address the vulnerability described in
    this advisory has been extracted from the SGI bulletin and is listed
    below.

       OS Version     Vulnerable?     Patch #      Other Actions
       ----------     -----------     -------      -------------

       IRIX 3.x          unknown      not avail    Note 1
       IRIX 4.x          unknown      not avail    Note 1
       IRIX 5.0.x        yes          not avail    Note 1
       IRIX 5.1.x        yes          not avail    Note 1
       IRIX 5.2          yes          not avail    Note 1
       IRIX 5.3          yes          2228
       IRIX 6.0.x        yes          not avail    Note 1
       IRIX 6.1          yes          not avail    Note 1
       IRIX 6.2          yes          2177
       IRIX 6.3          yes          2232
       IRIX 6.4          yes          2233

       NOTES

         1) upgrade operating system or see "Temporary Solution" section.

    "Temporary Solution" refers to the SGI bulletin but is equivalent to
    the suggestions given in our AUSCERT advisory in section 3.1.

    These patches can be retrieved from:

        http://www.sgi.com/Support/Secur/security.html

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 ) -type f -exec ls -l {} ;

    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, if sites had previously removed the setuid permissions
    for the eject program, they would not have been susceptible to this
    latest vulnerability.

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

The AUSCERT team have made every effort to ensure that the information
contained in this document is accurate.  However, the decision to use the
information described is the responsibility of each user or organisation.
The appropriateness of this document for an organisation or individual
system should be considered before application in conjunction with local
policies and procedures.  AUSCERT takes no responsibility for the
consequences of applying the contents of this document.

If you believe that your system has been compromised, contact AUSCERT or
your representative in FIRST (Forum of Incident Response and Security
Teams).

AUSCERT is located at The University of Queensland within the Prentice
Centre.  AUSCERT is a full member of the Forum of Incident Response and
Security Teams (FIRST).

AUSCERT maintains an anonymous FTP service which is found on:
ftp://ftp.auscert.org.au/pub/.  This archive contains past SERT and AUSCERT
Advisories, and other computer security information.

AUSCERT also maintains a World Wide Web service which is found on:
http://www.auscert.org.au/.

Internet Email: auscert@auscert.org.au
Facsimile:	(07) 3365 4477
Telephone:	(07) 3365 4417 (International: +61 7 3365 4417)
		AUSCERT personnel answer during Queensland business hours
		which are GMT+10:00 (AEST).
		On call after hours for emergencies.

Postal:
Australian Computer Emergency Response Team
Prentice Centre
Brisbane
Qld.  4072.
AUSTRALIA

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Revision History

17 Dec 1997     Silicon Graphics has released a security bulletin
                addressing the vulnerability described in this advisory.
                Section 3 has been modified to include vendor patch
                information.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

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