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Security Bulletin 9122                  DISA Defense Communications System
23 October 1991             Published by: DDN Security Coordination Center
                                      (SCC@NIC.DDN.MIL)   1-(800) 365-3642

                        DEFENSE  DATA  NETWORK
                          SECURITY  BULLETIN

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be  obtained  via  FTP  (or  Kermit)  from  NIC.DDN.MIL  [192.112.36.5]
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-9122).
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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 Information Systems Agency's Security             !
!     Coordination Center  distribution  system  as a  means  of        !
!     providing  DDN subscribers with useful security information.      !
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CA-91:20                        CERT Advisory
                              October 22, 1991
                        /usr/ucb/rdist Vulnerability

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The Computer Emergency Response Team/Coordination Center (CERT/CC) has
received information concerning a vulnerability in /usr/ucb/rdist (the 
location of rdist may vary depending on the operating system).  This 
vulnerability is present in possibly all versions of rdist.  Vendors 
responding with patches are listed below.  Additionally, some vendors 
who do not include rdist in their operating systems are identified.  
Operating systems from vendors not listed in either of the two categories 
below will probably be affected and the CERT/CC has proposed a workaround 
for those systems.

VENDORS THAT DO NOT SHIP rdist
(Note: Even though these vendors do not ship rdist, it may have been
       added later (for example, by the system administrator).  It is 
       also possible that vendors porting one of these operating systems 
       may have added rdist.  In both cases corrective action must be taken.)

  Amdahl
  AT&T System V 
  Data General DG/UX for AViiON Systems

	
VENDORS PROVIDING PATCHES 

  Cray Research, Inc.   UNICOS 6.0/6.E/6.1   Field Alert #132   SPR 47600

     For further information contact the Support Center at 1-800-950-CRAY or 
     612-683-5600 or e-mail support@crayamid.cray.com.

  NeXT Computer, Inc.  NeXTstep Release 2.x

     A new version of rdist may be obtained from your
     authorized NeXT Support Center.  If you are an authorized
     support center, please contact NeXT through your normal
     channels.  NeXT also plans to make this new version of
     rdist available on the public NeXT FTP archives.

  Silicon Graphics   IRIX 3.3.x/4.0 (fixed in 4.0.1)

     Patches may be obtained via anonymous ftp from sgi.com in the
     sgi/rdist directory.

  Sun Microsystems, Inc.   SunOS 4.0.3/4.1/4.1.1   Patch ID 100383-02

     Patches may be obtained via anonymous ftp from ftp.uu.net or from local
     Sun Answer Centers worldwide.


The CERT/CC is hopeful that other patches will be forthcoming.  We will
be maintaining a status file, rdist-patch-status, on the cert.sei.cmu.edu
system.  We will add patch availability information to this file as
it becomes known.  The file is available via anonymous ftp to
cert.sei.cmu.edu and is found in pub/cert_advisories/rdist-patch-status.

All trademarks are the property of their respective holders.
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I.   Description

     A security vulnerability exists in /usr/ucb/rdist that
     can be used to gain unauthorized privileges.  Under some
     circumstances /usr/ucb/rdist can be used to create setuid
     root programs.

II.  Impact

     Any user logged into the system can gain root access.

III. Solution
        
     A.  If available, install the appropriate patch provided by
         your operating system vendor.

     B.  If no patch is available, restrict the use of /usr/ucb/rdist
         by changing the permissions on the file.

         # chmod 711 /usr/ucb/rdist

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The CERT/CC wishes to thank Casper Dik of the University of Amsterdam,
The Netherlands, for bringing this vulnerability to our attention.
We would also like to thank the vendors who have responded to this problem.
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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(GMT-5)/EDT(GMT-4),
           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 (192.88.209.5) system.