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DDN Security Bulletin 9107      DCA DDN Defense Communications System
20 MAY 91               Published by: DDN Security Coordination Center
                                     (SCC@NIC.DDN.MIL)  (800) 235-3155

                        DEFENSE  DATA  NETWORK
                          SECURITY  BULLETIN

The DDN  SECURITY BULLETIN  is distributed  by the  DDN SCC  (Security
Coordination Center) under  DCA contract as  a means of  communicating
information on network and host security exposures, fixes, &  concerns
to security & management personnel at DDN facilities.  Back issues may
be  obtained  via  FTP  (or  Kermit)  from  NIC.DDN.MIL  [192.67.67.20]
using login="anonymous" and password="guest".  The bulletin pathname is
SCC:DDN-SECURITY-yynn (where "yy" is the year the bulletin is issued
and "nn" is a bulletin number, e.g. SCC:DDN-SECURITY-9001).
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            NeXT rexd, /private/etc, Username me Vulnerabilities

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!                                                                       !
!     The following important  advisory was  issued by the Computer     !
!     Emergency Response Team (CERT)  and is being relayed unedited     !
!     via the Defense Communications Agency's Security Coordination     !
!     Center  distribution  system  as a  means  of  providing  DDN     !
!     subscribers with useful security information.                     !
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CA-91:06                        CERT Advisory
                                 May 14, 1991
            NeXT rexd, /private/etc, Username me Vulnerabilities

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The Computer Emergency Response Team/Coordination Center (CERT/CC) and
NeXT Computer, Inc. have received information concerning three
vulnerabilities in NeXT computers running various releases (see below)
of NeXTstep software.  For more information, please contact your
authorized support center.  If you are an authorized support provider,
please contact NeXT through your normal channels.

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Problem 1 DESCRIPTION:  By default, rexd(8C) is enabled in NeXTstep
versions 2.0 and 2.1.  (Note that no NeXT software uses rexd.)

Problem 1 IMPACT:  Leaving rexd enabled allows remote users to execute
processes on a NeXT computer.

Problem 1 SOLUTION:  Comment out or remove the rexd line in
/etc/inetd.conf (unless you're using the remote execution facility),
and either restart the computer or cause inetd to re-read it's
configuration file, using:

        kill -HUP <inetd pid>



Problem 2 DESCRIPTION:  The /private/etc directory is shipped with
group write permission enabled in all NeXTstep versions through and
including 2.1.

Problem 2 IMPACT:  Group write permission in /private/etc enables any
user in the "wheel" group to modify files in the /private/etc
directory.

Problem 2 SOLUTION:  Turn off group write permission for the
/private/etc directory, using the command:

        chmod g-w /private/etc

or the equivalent operations from the Workspace Manager's Inspector
panel.



Problem 3 DESCRIPTION: Username "me" is a member of the "wheel" group
in all NeXTstep versions through and including 2.1.

Problem 3 IMPACT:  Having username "me" in the "wheel" group enables
"me" to use the su(8) command to become root (the user must still know
the root password, however).

Problem 3 SOLUTION:  Unless you have specific reason(s) not to, remove
the user "me" from the wheel group.


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The CERT/CC would like to thank NeXT Computer, Inc. for their response
to this vulnerability.  CERT/CC would also like to thank Fuat Baran
for his technical assistance.

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If you believe that your system has been compromised, contact CERT/CC
via telephone or e-mail.

Computer Emergency Response Team/Coordination Center (CERT/CC)
Software Engineering Institute
Carnegie Mellon University
Pittsburgh, PA 15213-3890

Internet E-mail: cert@cert.sei.cmu.edu
Telephone: 412-268-7090 24-hour hotline:
           CERT/CC personnel answer 7:30a.m.-6:00p.m. EST,
           on call for emergencies during other hours.

Past advisories and other computer security related information are
available for anonymous ftp from the cert.sei.cmu.edu (128.237.253.5)
system.