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CA-91:17 CERT Advisory
September 26, 1991
DECnet-Internet Gateway Vulnerability
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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.
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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.
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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.
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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:
[email protected]
Telephone: 412-268-7090 24-hour hotline:
CERT/CC personnel answer 7:30a.m.-6:00p.m. EST/EDT,
on call for emergencies during other hours.
Past advisories and other computer security related information are available
for anonymous ftp from the cert.org (192.88.209.5) system.
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