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Original issue date: September 26, 1991<BR>
Last revised: September 18, 1997<BR>
Attached copyright statement

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

<P>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.

<P>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.

<H2>I. Description</H2>

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.

<H2>II. Impact</H2>

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

<H2>III. Solution</H2>

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.


<P>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.


<!--#include virtual="/include/footer_nocopyright.html" -->
<P>Copyright 1991 Carnegie Mellon University.</P>


Revision History
September 18,1997  Attached Copyright Statement