SunOS NIS Vulnerability

Original issue date: June 4, 1992
Last revised: September 19, 1997
Attached copyright statement

A complete revision history is at the end of this file.

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 ( 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 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.

This document is available from:

CERT/CC Contact Information

Phone: +1 412-268-7090 (24-hour hotline)
Fax: +1 412-268-6989
Postal address:
CERT Coordination Center
Software Engineering Institute
Carnegie Mellon University
Pittsburgh PA 15213-3890

CERT/CC personnel answer the hotline 08:00-17:00 EST(GMT-5) / EDT(GMT-4) Monday through Friday; they are on call for emergencies during other hours, on U.S. holidays, and on weekends.

Using encryption

We strongly urge you to encrypt sensitive information sent by email.  Our public PGP key is available from

If you prefer to use DES, please call the CERT hotline for more information.

Getting security information

CERT publications and other security information are available from our web site

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Copyright 1992 Carnegie Mellon University.

Revision History
September 19,1997  Attached copyright statement