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CA-93:17                         CERT Advisory
                              November 11, 1993
                         xterm Logging Vulnerability
- -----------------------------------------------------------------------------

The CERT Coordination Center is working on eliminating a vulnerability in
xterm.  This vulnerability potentially affects all systems running xterm
with the setuid or setgid bit set.  This vulnerability has been found in
X Version 11, Release 5 (X11R5) and earlier versions of X11.

CERT is working with the vendor community to address this vulnerability.

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

I.   Description

    A vulnerability in the logging function of xterm exists in many
    versions of xterm that operate as a setuid or setgid process.  The
    vulnerability allows local users to create files or modify any
    existing files.

    If the setuid or setgid privilege bit is not set on the xterm program,
    the vulnerability cannot be exploited.

    It is possible that the xterm on your system does not allow
    logging.  In this case, the vulnerability cannot be exploited.  To
    determine if logging is enabled, run xterm with the "-l" option.  If
    an "XtermLog.axxxx" file is created in the current directory, xterm
    supports logging.  You can also check the output of "xterm -help"
    to see whether the "-l" option is described as "not supported".

    Another way to determine if logging is available is to look for
    the "Log to File" item in the Main Options menu (press Control mouse
    button 1).  If the X Consortium's public patch has been installed
    as distributed,  the option "Log to File" should not appear in the
    menu.


II.  Impact

    This vulnerability allows anyone with access to a user account
    to gain root access.


III. Solutions

    All of the following solutions require that a new version of xterm be
    installed.  When installing the new xterm, it is important either to
    remove the old version of xterm or to clear the setuid and setgid
    bits from the old xterm.

    CERT suggests one of the following solutions.

    A.  Install vendor supplied patch if available.  CERT is hopeful
        that patches will be forthcoming.  We will be maintaining a
        status file, xterm-patch-status, and we will add patch availability
        information to this file as it becomes known.  The file is
        available via anonymous FTP from info.cert.org.  The name of
        the file is pub/cert_advisories/xterm-patch-status.  A current
        version of this file is appended to this Advisory.

        For more up-to-date information, contact the vendor.

    B.  If your site is using the X Consortium's X11R5, install the
        public patch #26.  This patch is available via anonymous FTP
        from ftp.x.org as the file /pub/R5/fixes/fix-26.  Install all
        patch files up to and including fix-26.

        By default, the patch disables logging. If you choose to enable
        logging, a variation of the vulnerability still exists.

        Checksum information:

               BSD Unix Sum:  19609 47

               System V Sum:  51212 94

               MD5 Checksum:  e270560b6e497a0a71881d4ff4db8c05

    C.  If your site is using an earlier version of the X Consortium's X11,
        upgrade to X11R5.  Install all patches up to and including fix-26.

    D.  If you are unable to upgrade to the X Consortium's X11R5, modify
        the xterm source code to remove the logging feature.  Familiarity
        with X11 and its installation and configuration is recommended
        before implementing these modifications.

- ---------------------------------------------------------------------------
The CERT Coordination Center wishes to thank Stephen Gildea of the
X Consortium for his assistance in responding to this problem.
- ---------------------------------------------------------------------------

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

Internet E-mail: [email protected]
Telephone: 412-268-7090 (24-hour hotline)
          CERT personnel answer 8:30 a.m.-5:00 p.m. EST(GMT-5)/EDT(GMT-4),
          and are on call for emergencies during other hours.

CERT Coordination Center
Software Engineering Institute
Carnegie Mellon University
Pittsburgh, PA 15213-3890

Past advisories, information about FIRST representatives, and other
information related to computer security are available for anonymous
FTP from info.cert.org.

^L


                           CERT Coordination Center
                             xterm Vendor Status
                              November 11, 1993


This file is a supplement to the CERT Advisory CA-93:17 of November 11, 1993,
and will be updated as additional information becomes available.

The following is vendor-supplied information.  The CERT Coordination Center
will not formally review, evaluate, or endorse this information. For more
up-to-date information, contact your vendor.

It is important to note that the vendor of your xterm may not be the same
as the vendor of your platform.  You should take care to correctly identify
the vendor whose xterm you are using, so you can take the appropriate action.



       Convex     Fixed in CXwindows V3.1.  Fixed in CXwindows V3.0
                  with TAC patch V3.0.131 applied.  The Convex Technical
                  Assistance Center is available for additional information
                  at 800-952-0379.

       Cray       Fixed. Contact Cray for version/patch numbers.

       DEC/OSF    Attached is the information on the remedial images to
                  address the xterm issue for ULTRIX V4.3 (VAX & RISC)
                  and OSF/1 V1.2.   The solutions have been included in
                  ULTRIX V4.4 (VAX & RISC) and OSF/1 V1.3.

                  Customers may call their normal Digital Multivendor
                  Customer Services Support Channel to obtain this kit.

                  ----------------------------------------------------------
                  *ULTRIX,OSF/1] CSCPAT_4034 xterm Security Fix ECO Summary


                  COPYRIGHT (c) 1988, 1993 by Digital Equipment Corporation.
                  ALL RIGHTS RESERVED.

                  COMPONENT:  xterm

                  OP/SYS:     ULTRIX VAX and RISC, OSF/1

                  SOURCE:     Digital Customer Support Center

                  ECO INFORMATION:

                  CSCPAT Kit:                  CSCPAT_4034 V1.1
                  CSCPAT Kit Size:             2152 blocks
                  Engineering Cross Reference: SSRT93-E-0230, SSRT93-E-0231,
                                               SSRT93-E-232
                  Kit Applies To:              ULTRIX V4.3, OSF/1 V1.2
                  System Reboot Required:      NO
                  ----------------------------------------------------------

       SCO        The current releases listed below are not vulnerable to
                  this problem.  No xterm logging or scoterm logging is
                  provided:

                  SCO Open Desktop Lite, Release 3.0
                  SCO Open Desktop, Release 3.0
                  SCO Open Server Network System, Release 3.0
                  SCO Open Server Enterprise System, Release 3.0

                  Contact SCO for any further information.

       Sequent    Fixed. Contact Sequent for version/patch numbers.

       Sun        Sun's version of xterm has not been setuid root since at
                  least as far back as SunOS 4.1.1, and probably further.
                  An xterm that does not run setuid or setgid is not
                  vulnerable to the xterm logging problem.

                  CAUTION: A Sun patch was issued on December 6, 1992 to give
                  system administrators the option of running xterm setuid
                  root.  Installing this patch will introduce the xterm
                  logging vulnerability.  So check your xterm.  If either
                  the setuid or setgid privilege bit is set on the xterm
                  program, the vulnerability can be exploited.  Contact
                  Sun for further information.

       X.org      (Publicly distributed version of X.)  You can patch X11R5
                  by applying all patches up to and including fix-26.  See
                  the associated CERT Advisory (CA-93:17) for further
                  information.


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