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  • CERT Advisory CA-1990-06 NeXT's System Software

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Original issue date: October 3, 1990
Last revised: September 17, 1997
Attached Copyright statement

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

This message is an update of the October 2, 1990 CERT Advisory (CA-90.06). There is one correction and an update that you need to know about.

For Problem #2 SOLUTION, the following line has been added:

# /etc/chmod 440 /usr/lib/NextPrinter/npd.old
This will disable the old printer program. An updated copy of the CERT Advisory has been included with this message.

NeXT is also making the new printer program, npd, available electronically via anonymous ftp for Internet sites. The archives sites are:

In addition, NeXT has asked the CERT to announce that if anyone cannot get it from the archives, NeXT Technical Support can provide it. Requests should go to:


Computer Emergency Response Team

NeXT's System Software

This message is to alert administrators of NeXT Computers of four potentially serious security problems.

The information contained in this message has been provided by David Besemer, NeXT Computer, Inc. The following describes the four security problems, NeXT's recommended solutions and the 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.

Problem #1 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.

Problem #1 Solution

NeXT owners running Release 1.0 or 1.0a should remove /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 system 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.

Problem #2 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.

Problem #2 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. 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.

Problem #3 Impact

This security problem will enable an intruder to gain access to the system.

Problem #3 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.

Problem #4 Impact

Allows a user to gain root access.

Problem #4 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
  6. (where ~newuser is the home directory of the new user account)

  7. Set the protections appropriately using the following command:
  8.  # chmod 555 /usr/template/user/.NeXT/.dock

  9. 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. CONTACT INFORMATION

For further questions, please contact your NeXT support center.

NeXT has also reported that these potential problems have been fixed in NeXT's Release 2.0, which will be available in November, 1990.

Thanks to Corey Satten and Scott Dickson for discovering, documenting, and helping resolve these problems.

Copyright 1990 Carnegie Mellon University.

Revision History
September 17,1997 Attached Copyright statement
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