DECnet-Internet Gateway Vulnerability

Original issue date: September 26, 1991
Last revised: September 18, 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 a vulnerability in the configuration of the DECnet-Internet gateway software for Digital Equipment Corporation's (DEC) ULTRIX versions 4.0, 4.1, and 4.2 on all Digital architectures.

Digital Equipment Corporation is aware of this problem and a resolution for this vulnerability will be included in a future release.  Digital and the CERT/CC strongly recommend that sites exposed to this vulnerability immediately institute the workaround detailed in this advisory.

I. Description

When installing the DECnet-Internet gateway software it is necessary to create a guest account on the ULTRIX gateway host.  By default, this account has /bin/csh as its shell.  By virtue of the guest account having a valid shell, the DECnet-Internet gateway software can be exploited to allow unauthorized root access.

II. Impact

Anyone using the DECnet-Internet gateway can gain unauthorized root privileges on the ULTRIX gateway host.

III. Solution

This section describes a workaround for this vulnerability. Disable the guest account by editing the /etc/passwd file and setting the shell field for the guest account to /bin/false.  Also, ensure the guest account has the string "NoLogin" in the password field as detailed in the DECnet-Internet installation manual.  Even if you have not installed or are not running the DECnet- Internet gateway software, Digital recommends that you implement the workaround solution stated above.

The CERT/CC wishes to thank R. Scott Butler of the Du Pont Company for bringing this vulnerability to our attention and for his further assistance with the temporary workaround.

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

* "CERT" and "CERT Coordination Center" are registered in the U.S. Patent and Trademark Office.

Any material furnished by Carnegie Mellon University and the Software Engineering Institute is furnished on an "as is" basis. Carnegie Mellon University makes no warranties of any kind, either expressed or implied as to any matter including, but not limited to, warranty of fitness for a particular purpose or merchantability, exclusivity or results obtained from use of the material. Carnegie Mellon University does not make any warranty of any kind with respect to freedom from patent, trademark, or copyright infringement.

Conditions for use, disclaimers, and sponsorship information

Copyright 1991 Carnegie Mellon University.

Revision History
September 18,1997  Attached Copyright Statement