************************************************************************** Security Bulletin 9119 DISA Defense Communications System 3 October 1991 Published by: DDN Security Coordination Center (SCC@NIC.DDN.MIL) 1-(800) 365-3642 DEFENSE DATA NETWORK SECURITY BULLETIN The DDN SECURITY BULLETIN is distributed by the DDN SCC (Security Coordination Center) under DISA 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 [192.112.36.5] 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-9119). ************************************************************************** + - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - + ! ! ! The following important advisory was issued by the Computer ! ! Emergency Response Team (CERT) and is being relayed unedited ! ! via the Defense Information Systems Agency's Security ! ! Coordination Center distribution system as a means of ! ! providing DDN subscribers with useful security information. ! ! ! + - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - + DISTRIBUTION RESTRICTIONS: PUBLIC RELEASE Enclosed is the final draft of a CERT Advisory. If reprinted, in part or whole, please credit the: Computer Emergency Response Team/Coordination Center (CERT/CC) =========================================================================== CA-91:18 CERT Advisory September 27, 1991 Active Internet tftp Attacks --------------------------------------------------------------------------- The Computer Emergency Response Team/Coordination Center (CERT/CC) would like to alert you to automated tftp probes that have been occurring over the last few days. These probes have attacked Internet sites throughout the world and in most cases the file retrieved was /etc/passwd. However, other files such as /etc/rc may have been retrieved. The CERT/CC is working with the site(s) that were used by intruders to launch the attacks. We are actively contacting those sites where we believe the retrievals were successful. We are urging all sites to carefully check their system configurations concerning tftp usage. --------------------------------------------------------------------------- I. Description Unrestricted tftp access allows remote sites to retrieve a copy of any world-readable file. II. Impact Anyone on the Internet can use tftp to retrieve copies of a site's sensitive files. For example, the recent incident involved retrieving /etc/passwd. The intruder can later crack the password file and use the information to login to the accounts. This method may provide access to the root account. III. Solution A. Sites that do not need tftp should disable it immediately by editing the system configuration file to comment out, or remove, the line for tftpd. This file may be /etc/inetd.conf, /etc/servers, or another file depending on your operating system. To cause the change to be effective, it will be necessary to restart inetd or force inetd to read the updated configuration file. B. Sites that must use tftp (for example, for booting diskless clients) should configure it such that the home directory is changed. Example lines from /etc/inetd.conf might look like: ULTRIX 4.0 tftp dgram udp nowait /etc/tftpd tftpd -r /tftpboot SunOS 4.1 tftp dgram udp wait root /usr/etc/in.tftpd in.tftpd -s /tftpboot As in item A. above, inetd must be restarted or forced to read the updated configuration file to make the change effective. C. If your system has had tftp configured as unrestricted, the CERT/CC urges you to consider taking one of the steps outlined above and change all the passwords on your system. --------------------------------------------------------------------------- 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/EDT, 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. Posted-Date: Fri, 27 Sep 91 16:20:58 EDT Received-Date: Fri, 27 Sep 91 16:19:38 EDT Full-Name: John P. Wack Organization: National Institute of Standards and Technology (NIST) Sub-Organization: Computer Security Division Return-Path: