CERT Advisory - xterm Logging Vulnerability

CERT Advisory cert-advisory-request at cert.org
Thu Nov 11 23:47:30 UTC 1993

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

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: cert at cert.org
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.



                            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,
                   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

                   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 

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