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CERT Advisory 102
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CERT(sm) Advisory CA-95:15
Original issue date: November 8, 1995
Last revised: August 30, 1996
Information previously in the README was inserted
into the advisory.
A complete revision history is at the end of this file.
Topic: SGI lp Vulnerability
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The CERT Coordination Center has had several security incidents reported to us
involving the lp account on the Silicon Graphics, Inc. (SGI) IRIX system. As
distributed by SGI, the lp account, as well as other accounts, has no password
on a newly installed system. The lp account, which is used by the lp(1)
program for remote printing, and other accounts are initially configured
without passwords to provide easy "plug-and-play" install and operation.
However, these password-less accounts are well known by intruders and allow
unintended access to your system.
In the documentation that SGI distributes with their systems, these
password-less accounts are specifically addressed in the "IRIX Advanced Site
and Server Administrative Guide" in the chapter on System Security. The
documentation recommends disabling the login for the lp account. It also
recommends that you create passwords for the following accounts immediately:
demos, guest, lp, nuucp, root, tour, tutor, and 4Dgifts. The documentation
includes guidelines for choosing good passwords.
To determine if your system is vulnerable, use the following command as
root to display the status of all password-less accounts:
# /bin/passwd -sa | /bin/awk '$2 == "NP" {print $0}'
If this command displays any accounts, especially the lp account, then
your system is vulnerable. To address this vulnerability, we recommend
using the workarounds in Section III below.
We will update this advisory as we receive additional information.
Please check advisory files regularly for updates that relate to your site.
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I. Description
The SGI IRIX system as distributed has some accounts without
passwords. Among the accounts that are password-less is the lp
account. This account is used in part by the lp(1) program to manage
object and spooled data files in the /var/spool/lp directory (for IRIX
4.X, this directory is /usr/spool/lp). The account is created without a
password because lp(1) uses rsh(1) to transfer files from print clients
to print servers.
II. Impact
Remote users can gain access to systems without authentication. The level
of privilege gained depends on the password-less account used to access a
system.
Although the scope of this advisory is the lp account, keep in mind that
any account without a password (or with an easy-to-guess password) is a
point for access without authentication.
III. Solution
The general solution is to lock all accounts that do not have
passwords. Section A below describes how to do that.
Section B suggests one way to re-enable print client to print server
communication.
A. Lock each password-less account.
Store the following script in /tmp/CheckPasswords for example and
then run it as root on your machine to lock each password-less
account. The password installed will not allow the accounts to be
used as login accounts. See the passwd(1) manual page for more
details. Note that this script only locks accounts on the local
machine. If there are password-less accounts in NIS, those accounts
will not be locked by this script.
------------------------cut here--8<------------------------
#!/bin/sh
for account in `/bin/passwd -sa | /bin/awk '$2 == "NP" {print $1}'`
do
/bin/echo Locked the $account account
/bin/passwd -l $account
done
------------------------cut here--8<------------------------
The first time the script is run, it should display something
similar to the following:
# sh /tmp/CheckPasswords
Locked the tutor account
Locked the tour account
Locked the lp account
...
If the script locked an account, run the script again. This
time it should produce no output because all password-less
accounts have now been locked.
B. Re-enable print client to print server communication.
(We have verified with SGI that you can use the script in this section
to re-enable the print client to print server communication. SGI has
asked us to make it clear, however, that they do not have the
resources to handle issues relating to the use of wrappers.)
Note that, in general, the CERT Coordination Center recommends
that the rlogin and rsh services be blocked at your Internet
routers and turned off on all of your machines. If you have turned
the rsh service off on your print server, you will need to turn it
back on on that machine. If you decide to do this, we strongly
recommend that you install and use a TCP/IP wrapper program to
restrict the set of machines that can connect to your print server's
rsh service. A TCP/IP wrapper program is available from
ftp://info.cert.org/pub/tools/tcp_wrappers/tcp_wrappers_7.2.tar.Z
MD5 (tcp_wrappers_7.2.tar.Z) = 883d00cbd2dedd9bfc783b7065740e74
Once the rsh service is turned on on your print server and a TCP/IP
wrapper program installed and configured, you then need to define
the set of machines that can communicate with your print server.
For each IRIX system that controls a printer, the lp account
needs to be changed to re-enable print client to print server
communication. To do this, the lp account on each print server
needs a .rhosts file in lp's home directory, typically
/var/spool/lp (for IRIX 4.X, this directory is /usr/spool/lp).
The owner and group of this file must be the same as that of the
lp account. Its contents are lines of the form:
print_client_name lp
Each line identifies the name of the print client and indicates
that the lp account is the account that is allowed to rsh from
the print client to the print server.
The following shows an example of configuring communication from
a print client (named "client") to a print server. This
configuration need only be done on a print server. The ping
command is used to determine the print client's formal name
according to whatever host resolution scheme is in place.
That name is stored in the .rhosts file. The last two lines,
the ping and the echo, need to be repeated for each client of
a print server.
# /bin/awk -F: '$1 == "lp" {print $0}' /etc/passwd
lp:*LK*:9:9:Print Spooler Owner:/var/spool/lp:/bin/sh
# cd `/bin/awk -F: '$1 == "lp" {print $6}' /etc/passwd`
# /bin/touch .rhosts
# /bin/chown lp .rhosts
# /bin/chgrp lp .rhosts
# /bin/chmod 600 .rhosts
# /usr/etc/ping -c 1 client | /bin/awk '$1 == "PING" {print $2}'
client.YourDomain
# /bin/echo client.YourDomain lp >> .rhosts
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The CERT Coordination Center staff thanks Silicon Graphics Inc. and
Christopher Kranz of Princeton University for their support in responding to
this problem.
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If you believe that your system has been compromised, contact the CERT
Coordination Center or your representative in the Forum of Incident
Response and Security Teams (FIRST).
If you wish to send sensitive incident or vulnerability information to
CERT staff by electronic mail, we strongly advise that the email be
encrypted. The CERT Coordination Center can support a shared DES key, PGP
(public key available via anonymous FTP on info.cert.org), or PEM (contact
CERT staff for details).
Internet email: cert@cert.org
Telephone: +1 412-268-7090 (24-hour hotline)
CERT personnel answer 8:30 a.m.-5:00 p.m. EST(GMT-5)/EDT(GMT-4),
and are on call for emergencies during other hours.
Fax: +1 412-268-6989
Postal address: CERT Coordination Center
Software Engineering Institute
Carnegie Mellon University
Pittsburgh, PA 15213-3890
USA
CERT advisories and bulletins are posted on the USENET newsgroup
comp.security.announce. If you would like to have future advisories and
bulletins mailed to you or to a mail exploder at your site, please send mail
to cert-advisory-request@cert.org.
Past CERT publications, information about FIRST representatives, and
other information related to computer security are available for anonymous
FTP from info.cert.org.
Copyright 1995, 1996 Carnegie Mellon University
This material may be reproduced and distributed without permission provided it
is used for non commercial purposes and the copyright statement is included.
CERT is a service mark of Carnegie Mellon University.
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UPDATES
Silicon Graphics, Inc. have issued a Security Advisory
concerning this vulnerability (19951002-01-I). Their advisory
can be obtained from
ftp://sgigate.sgi.com/security
We have received additional information from one member of our
constituency regarding the vulnerability in the SGI printing system
and the accounts without passwords. The supercomputer NEC SX-3 running
"SUPER-UX unix 5.10 1 SX-3" (which is very similar to IRIX) also has
the same vulnerability.
(As far as we are aware there are only about 30 machines [in the world]
running this OS.)
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Revision history
Aug. 30, 1996 Information previously in the README was inserted
into the advisory.
Dec. 20, 1995 Updates section - Added a pointer to SGI advisory and a note
about the supercomputer NEC SX-3.
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