CERT Advisory - SunOS NIS Vulnerability

CERT Advisory cert-advisory-request at cert.org
Thu Jun 4 19:13:22 UTC 1992

CA-92:13                       CERT Advisory
                               June 4, 1992
                          SunOS NIS Vulnerability

The Computer Emergency Response Team/Coordination Center (CERT/CC) has
received information concerning several vulnerabilities with NIS under
Sun Microsystems, Inc. SunOS.  These vulnerabilities exist in NIS under
SunOS 4.1, 4.1.1, and 4.1.2, and may or may not exist in earlier versions
of NIS.

Sun has provided fixes for SunOS 4.1, 4.1.1, and 4.1.2 for these
vulnerabilities.  The patch file containing these fixes is available
through your local Sun Answer Center and through anonymous ftp from
ftp.uu.net ( in the /systems/sun/sun-dist directory.  Note
that these fixes will probably not be compatible with SunOS 4.0.3 and
earlier versions of the operating system.

Fix                              PatchID      Filename            Checksum
/usr/etc/{ypserv,ypxfrd,portmap} 100482-2     100482-02.tar.Z     53416   284

Please note that Sun will occasionally update patch files.  If you
find that the checksum is different, please contact Sun or the CERT/CC
for verification.


I.   Description

     A security vulnerability exists under NIS allowing unauthorized access
     to NIS information.

II.  Impact

     A user on a remote host can obtain copies of the NIS maps from a
     system running NIS.  The remote user can attempt to guess passwords
     for the system using the obtained NIS password map information.

III. Solution

     A.  Obtain and install the patch from Sun or from ftp.uu.net following
         the instructions provided in the "README" file.  

         1.  As root, rename the existing versions of
             /usr/etc/{ypserv,ypxfrd,portmap} and modify the
             permissions to prevent misuse.

             # mv /usr/etc/ypserv /usr/etc/ypserv.orig
             # mv /usr/etc/ypxfrd /usr/etc/ypxfrd.orig
             # mv /usr/etc/portmap /usr/etc/portmap.orig
             # chmod 0400 /usr/etc/ypserv.orig 
             # chmod 0400 /usr/etc/ypxfrd.orig
             # chmod 0400 /usr/etc/portmap.orig

         2.  Copy the new binaries into the /usr/etc directory.

             # cp `arch`/{4.1, 4.1.1, 4.1.2}/ypserv /usr/etc/ypserv
             # cp `arch`/{4.1, 4.1.1, 4.1.2}/ypxfrd /usr/etc/ypxfrd
             # cp `arch`/{4.1, 4.1.1, 4.1.2}/portmap /usr/etc/portmap
             # chown root /usr/etc/ypserv /usr/etc/ypxfrd /usr/etc/portmap
             # chmod 755 /usr/etc/ypserv /usr/etc/ypxfrd /usr/etc/portmap

         3.  Copy the securenets file to the /var/yp directory.  Any
             site that has an existing /var/yp/securenets file should 
             rename it prior copying the new version of the file.

             # cp `arch`/{4.1, 4.1.1, 4.1.2}/securenets /var/yp
             # chown root /var/yp/securenets
             # chmod 644 /var/yp/securenets

         4.  Edit the /var/yp/securenets file to reflect the correct
             configuration for your site.  See the "README" file for
             details of the file syntax and special instructions for
             hosts with multiple Ethernet interfaces.  The file should
             not contain any blank lines.
         5.  Reboot the system to invoke the new binaries.

The CERT/CC would like to thank Casper Dik of the University of Amsterdam,
The Netherlands, and Peter Lamb of the Division of Information Technology,
Commonwealth Scientific and Industrial Research Organization, Australia,
for their assistance.  We also wish to thank Sun Microsystems, Inc. for
their response to this vulnerability.

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

Internet E-mail: cert at cert.org
Telephone: 412-268-7090 (24-hour hotline)
           CERT/CC personnel answer 7:30 a.m.-6:00 p.m. EST(GMT-5)/EDT(GMT-4),
           on call for emergencies during other hours.

Computer Emergency Response Team/Coordination Center (CERT/CC)
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 cert.org (

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