*********************************************************************** DDN Security Bulletin 9112 DCA DDN Defense Communications System 23 August 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). ********************************************************************** Trusted Hosts Configuration Vulnerability + - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - + ! ! ! 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-91:12 CERT Advisory August 22, 1991 Trusted Hosts Configuration Vulnerability --------------------------------------------------------------------------- The Computer Emergency Response Team/Coordination Center (CERT/CC) has received information concerning a vulnerability in the configuration of several system files. This advisory discusses a workaround since there are no permanent patches available at this time. This vulnerability is present in a very large number of UNIX-based operating systems. Therefore, we recommend that ALL sites take the corrective actions listed below. --------------------------------------------------------------------------- I. DESCRIPTION: The presence of a '-' as the first character in /etc/hosts.equiv, /etc/hosts.lpd and .rhosts files may allow unauthorized access to the system. II. IMPACT: Remote users can gain unauthorized root access to the system. III. SOLUTION: Rearrange the order of entries in the hosts.equiv, hosts.lpd, and .rhosts files so that the first line does not contain a leading '-' character. Remove hosts.equiv, hosts.lpd, and .rhosts files containing only entries beginning with a '-' character. .rhosts files in ALL accounts, including root, bin, sys, news, etc., should be examined and modified as required. .rhosts files that are not needed should be removed. Please note that the CERT/CC strongly cautions sites about the use of hosts.equiv and .rhosts files. We suggest that they NOT be used unless absolutely necessary. --------------------------------------------------------------------------- The CERT/CC wishes to thank Alan Marcum, NeXT Computer, for bringing this security vulnerability to our attention. We would also like to thank CIAC for their assistance in testing this vulnerability. --------------------------------------------------------------------------- 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 (192.88.209.5) system.