*********************************************************************** DDN Security Bulletin 9107 DCA DDN Defense Communications System 20 MAY 91 Published by: DDN Security Coordination Center (SCC@NIC.DDN.MIL) (800) 235-3155 DEFENSE DATA NETWORK SECURITY BULLETIN The DDN SECURITY BULLETIN is distributed by the DDN SCC (Security Coordination Center) under DCA contract as a means of communicating information on network and host security exposures, fixes, & concerns to security & management personnel at DDN facilities. Back issues may be obtained via FTP (or Kermit) from NIC.DDN.MIL [192.67.67.20] using login="anonymous" and password="guest". The bulletin pathname is SCC:DDN-SECURITY-yynn (where "yy" is the year the bulletin is issued and "nn" is a bulletin number, e.g. SCC:DDN-SECURITY-9001). ********************************************************************** NeXT rexd, /private/etc, Username me Vulnerabilities + - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - + ! ! ! The following important advisory was issued by the Computer ! ! Emergency Response Team (CERT) and is being relayed unedited ! ! via the Defense Communications Agency's Security Coordination ! ! Center distribution system as a means of providing DDN ! ! subscribers with useful security information. ! ! ! + - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - + CA-91:06 CERT Advisory May 14, 1991 NeXT rexd, /private/etc, Username me Vulnerabilities --------------------------------------------------------------------------- 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. --------------------------------------------------------------------------- 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: cert@cert.sei.cmu.edu Telephone: 412-268-7090 24-hour hotline: CERT/CC personnel answer 7:30a.m.-6:00p.m. EST, on call for emergencies during other hours. Past advisories and other computer security related information are available for anonymous ftp from the cert.sei.cmu.edu (128.237.253.5) system.