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CIAC B-01
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The Computer Incident Advisory Capability
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Informational Bulletin
Security Problem on the NeXT Operating System
October 5, 1990, 0800 PST Number B-1
CIAC has been informed of a series of security problems in the NeXT
operating system that are now becoming well known. If your site
operates NeXT machines, CIAC recommends that you follow the procedures
below to secure these systems against attack. The information
contained in this message has been provided by David Besemer, NeXT
Computer, Inc. and from the Computer Emergency Response Team (CERT).
The following describes four potential security problems and NeXT
Computer's recommended solutions and known system impact.
Problem 1. DESCRIPTION: On Release 1.0 and 1.0a, a script exists in
/usr/etc/restore0.9 that is a setuid shell script. The existence of
this script is a potential security problem.
IMPACT: The script is only needed during the installation process and
isn't needed for normal usage. It is possible for any logged in user
to gain root access.
SOLUTION: NeXT owners running Release 1.0 or 1.0a should remove the
file /usr/etc/restore0.9 from all disks. This file is installed by the
"BuildDisk" application, so it should be removed from all systems built
with the standard release disk, as well as from the standard release
disk itself (which will prevent the file from being installed on
systems built with the standard release disk in the future). You must
be root to remove this script, and the command that will remove the
script is the following:
# /bin/rm /usr/etc/restore0.9
Problem 2.
DESCRIPTION: On NeXT computers running Release 1.0 or 1.0a that also
have publicly accessible printers, users can gain extra permissions
via a combination of bugs.
IMPACT: Computer intruders are able to exploit this security problem to
gain access to the system. Intruders, local users and remote users are
able to gain root access.
SOLUTION: NeXT computer owners running Release 1.0 or 1.0a should do
two things to fix a potential security problem. First, the binary
/usr/lib/NextPrinter/npd must be replaced with a more secure version.
This more secure version of npd is available through your NeXT support
center. You may contact this support center using electronic mail to:
ask_next@NeXT.com. This patched npd is also available by anonymous FTP
on the nodes nova.cc.purdue.edu, umd5.umd.edu, and cs.orst.edu. You
may also contact CIAC for help in obtaining this patch. Upon receiving
a copy of the more secure npd, you must become root and install it in
place of the old one in /usr/lib/NextPrinter/npd. The new npd binary
needs to be installed with the same permission bits (6755) and owner
(root) as the old npd binary. The commands to install the new npd
binary are the following:
# /bin/mv /usr/lib/NextPrinter/npd /usr/lib/NextPrinter/npd.old
# /bin/mv newnpd /usr/lib/NextPrinter/npd
(In the above command, "newnpd" is the npd binary that you obtained
from your NeXT support center.)
# /etc/chown root /usr/lib/NextPrinter/npd
# /etc/chmod 6755 /usr/lib/NextPrinter/npd
# /etc/chmod 440 /usr/lib/NextPrinter/npd.old
The second half of the fix to this potential problem is to change the
permissions of directories on the system that are currently owned and
able to be written by group "wheel". The command that will remove
write permission for directories owned and writable by group "wheel" is
below. This command is all one line, and should be run as root.
# find / -group wheel ! -type l -perm -20 ! -perm -2 -ls -exec chmod
g-w {} \; -o -fstype nfs -prune
Problem 3.
DESCRIPTION: On NeXT computers running any release of the system
software, public access to the window server may be a potential
security problem.The default in Release 1.0 or 1.0a is correctly set so
that public access to the window server is not available. It is
possible, when upgrading from a prior release, that the old
configuration files will be reused. These old configuration files
could possibly enable public access to the window server.
IMPACT: This security problem will enable an intruder to gain access to
the system.
SOLUTION: If public access isn't needed, it should be disabled.
1. Launch the Preferences application, which is located in /NextApps 2.
Select the UNIX panel by pressing the button with the UNIX certificate
on it.
3. If the box next to Public Window Server contains a check, click on
the box to remove the check.
Problem 4.
DESCRIPTION: On NeXT computers running any release of the system
software, the "BuildDisk" application is executable by all users.
IMPACT: Allows a user to gain root access.
SOLUTION: Change the permissions on the "BuildDisk" application
allowing only root to execute it. This can be accomplished with the
command:
# chmod 4700 /NextApps/BuildDisk
To remove "BuildDisk" from the default icon dock for new users, do the
following:
1. Create a new user account using the UserManager application.
2. Log into the machine as that new user.
3. Remove the BuildDisk application from the Application Dock by
dragging it out.
4. Log out of the new account and log back in as root.
5. Copy the file in ~newuser/.NeXT/.dock to
/usr/template/user/.NeXT/.dock
(where ~newuser is the home directory of the new user account)
6. Set the protections appropriately using the following command:
# chmod 555 /usr/template/user/.NeXT/.dock
7. If you wish, with UserManager, remove the user account that you
created in step 1.
In release 2.0, the BuildDisk application will prompt for the root
password if it is run by a normal user.
NeXT has also reported that these potential problems have been fixed in
NeXT's Release 2.0, which will be available in November, 1990. For
additional information or assistance, please contact CIAC or your NeXT
support center.
Tom Longstaff
(415) 423-4416 or (FTS) 543-4416
or
David Brown
(415) 423-9878 or (FTS) 543-9878
FAX: (415) 423-0913 or (FTS) 543-0913
or send e-mail to:
ciac@tiger.llnl.gov
Thanks to Corey Satten and Scott Dickson for discovering, documenting,
and helping resolve these problems.
Neither the United States Government nor the University of California
nor any of their employees, makes any warranty, expressed or implied,
or assumes any legal liability or responsibility for the accuracy,
completeness, or usefulness of any information, product, or process
disclosed, or represents that its use would not infringe privately
owned rights. Reference herein to any specific commercial products,
process, or service by trade name, trademark manufacturer, or
otherwise, does not necessarily constitute or imply its endorsement,
recommendation, or favoring by the United States Government or the
University of California. The views and opinions of authors expressed
herein do not necessarily state or reflect those of the United States
Government nor the University of California, and shall not be used for
advertising or product endorsement purposes.
