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  • CERT Advisory CA-1991-06 NeXT rexd, /private/etc, Username me Vulnerabilities

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Original issue date: May 14, 1991
Last revised: September 18, 1997
Attached copyright statement

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

The Computer Emergency Response Team/Coordination Center (CERT/CC) and NeXT Computer, Inc. have received information concerning three vulnerabilities in NeXT computers running various releases (see below) of NeXTstep software. For more information, please contact your authorized support center. If you are an authorized support provider, please contact NeXT through your normal channels.


PROBLEM 1 Description

By default, rexd(8C) is enabled in NeXTstep versions 2.0 and 2.1.
(Note that no NeXT software uses rexd.)

PROBLEM 1 Impact

Leaving rexd enabled allows remote users to execute processes on a NeXT computer.

PROBLEM 1 Solution

Comment out or remove the rexd line in /etc/inetd.conf (unless you're using the remote execution facility), and either restart the computer or cause inetd to re-read it's configuration file, using:
kill -HUP 

PROBLEM 2 Description

The /private/etc directory is shipped with group write permission enabled in all NeXTstep versions through and including 2.1.

PROBLEM 2 Impact

Group write permission in /private/etc enables any user in the "wheel" group to modify files in the /private/etc directory.

PROBLEM 2 Solution

Turn off group write permission for the /private/etc directory, using the command:
chmod g-w /private/etc
or the equivalent operations from the Workspace Manager's Inspector panel.


PROBLEM 3 Description

Username "me" is a member of the "wheel" group in all NeXTstep versions through and including 2.1.

PROBLEM 3 Impact

Having username "me" in the "wheel" group enables "me" to use the su(8) command to become root (the user must still know the root password, however).

PROBLEM 3 Solution

Unless you have specific reason(s) not to, remove the user "me" from the wheel group.


The CERT/CC would like to thank NeXT Computer, Inc. for their response to this vulnerability. CERT/CC would also like to thank Fuat Baran for his technical assistance.

Copyright 1991 Carnegie Mellon University.


Revision History
September 18,1997  Attached Copyright Statement
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