=============================================================================== CA-91:13 CERT Advisory August 23, 1991 DEC ULTRIX /usr/bin/mail Vulnerability ------------------------------------------------------------------------------- The Computer Emergency Response Team/Coordination Center (CERT/CC) has received information concerning a vulnerability in all versions of Digital Equipment Corporation's (DEC) ULTRIX operating system prior to 4.2 and applicable to all Digital Equipment Corporation architectures. The vulnerability has been fixed in ULTRIX version 4.2. This vulnerability allows any user logged into the system to obtain a root shell. Appended is an update to a Digital Equipment Corporation DSNlink/ DSIN FLASH which describes the vulnerability and Digital Equipment Corporation's recommended solution. If you have any inquiries regarding Digital Equipment Corporation's document, please contact your Digital Services Support Organization. =============================================================================== Start of Digital Equipment Corporation's Document. ------------------------------------------------------------------------------- SOURCE: Digital Equipment Corporation. COPYRIGHT (c) 1988, 1989, 1990 by Digital Equipment Corporation. ALL RIGHTS RESERVED. INFORMATION: ULTRIX V4.1 - Security Vulnerability Identified in /usr/bin/mail PROBLEM: A potential security vulnerability has been identified in ULTRIX Version 4.1 where, under certain circumstances, user privileges can be expanded via /usr/bin/mail. This problem applies to both the VAX and DEC RISC (i.e. DECsystem and DECstation ) architectures. As always, Digital urges you to regularly review your system management and security procedures. Digital will continue to review and enhance security features, and work with our customers to further improve the integrity of their systems. SOLUTION: Digital has corrected the identified code as of ULTRIX Version 4.2 (released May 1991). Digital recommends strongly that you upgrade to ULTRIX Version 4.2 immediately to avoid any potential vulnerability to your system via this problem. For those of you who are unable to upgrade at this time, installing the ULTRIX Version 4.2 mail file on your V4.1 system will correct this problem. ULTRIX Version 4.2 of /usr/bin/mail has not been shown to be compatible with versions of ULTRIX previous to ULTRIX version 4.1; upgrading to ULTRIX V4.2 or upgrading to ULTRIX V4.1 and using the ULTRIX 4.2 /usr/bin/mail program is required to correct this problem. Use one of the procedures below to update an ULTRIX Version 4.1 system: - Procedure (1) describes the process to extract the /usr/bin/mail binary from the ULTRIX Version 4.2 MUP subset. - Procedure (2) provides the commands to install the ULTRIX Version 4.2 /usr/bin/mail binary from another of your system(s) where possible. - Both the VAX (DECsystem) and DEC RISC (DECstation) versions of the ULTRIX Version 4.2 /usr/bin/mail binary, may be obtained by contacting your Digital Services Support Organization. ------------------------------------------------------------------------------- (1) This procedure will replace your existing /usr/bin/mail binary using the /usr/bin/mail binary from the ULTRIX Version 4.2 MUP distribution. The procedure below describes the method to extract the binary from the tape media. NOTE: Setting the environment to single user mode will prevent possible disruption of the mail services. ------------------------------------------------------------------------------- To update an ULTRIX Version 4.1 system, you must first obtain the ULTRIX Version 4.2 binary of /usr/bin/mail for your computer's architecture from your ULTRIX Version 4.2 distribution tapes. LOAD THE ULTRIX MANDATORY UPGRADE TAPE ON YOUR ULTRIX Version 4.1 SYSTEM. ( Note: UDTBASE421 will provide the RISC base upgrade, ULTBASE421 will) ( provide the VAX base upgrade mail file. Substitute as necessary for) ( your architecture. ) ( ISSUE THE FOLLOWING COMMANDS FROM YOUR ULTRIX Version 4.1 SYSTEM ) ( BECOME ROOT - YOU MUST HAVE PRIVILEGES TO MAKE THIS UPDATE. ) % su (cd TO SOME DIRECTORY THAT YOU CAN PUT THE FILE IN TEMPORARILY, e.g. cd /tmp) # cd /tmp (NOTE: YOU WILL NEED APPROXIMATELY 2 MB of DISK SPACE ) # mkdir ./usr # mkdir ./usr/etc # mkdir ./usr/etc/subsets # setld -x /dev/nrmt0h {UDTBASE421 or ULTBASE421} ( LIST THE SUBSET, CREATE THE FILE UDTBASE421 or ULTBASE0421, THEN EXTRACT ) ( THE MAIL FILE /usr/bin/mail {NOTE} THIS EXAMPLE USES THE "RISC" SUBSET ) # ls # mv UDTBASE421 UDTBASE421.Z # zcat UDTBASE421.Z | tar xvf - ./usr/bin/mail ( MOVE THE ULTRIX V4.2 BINARY TO /usr/bin/mail CHANGE PROTECTION, OWNER etc.) # cd /usr/bin # mv mail mail.old # chmod 600 mail.old # mv /tmp/usr/bin/mail . # chown root mail # chgrp kmem mail # chmod 6755 mail ------------------------------------------------------------------------------- (2) To update the /usr/bin/mail binary from an existing V4.2 (similar platform (VAX or RISC)) remote node, copy the file to your system and store it in a temporary location (e.g., - /tmp/mail). The procedure below provides an example using DECnet. Use the copy command that fits your environment to copy the /usr/bin/mail binary from a remote node to the /tmp directory on your local system. NOTE: Setting the environment to single user mode will prevent possible disruption of the mail services. ------------------------------------------------------------------------------- % dcp -iv {remote-nodename}/{username}/{password}::'/usr/bin/mail' '/tmp/mail' ( ISSUE THE FOLLOWING COMMANDS FROM YOUR ULTRIX Version 4.1 SYSTEM ) ( BECOME ROOT - YOU MUST HAVE PRIVILEGES TO MAKE THIS UPDATE. ) % su # cd /usr/bin # mv mail mail.old # chmod 600 mail.old ( MOVE THE ULTRIX V4.2 BINARY TO /usr/bin/mail CHANGE PROTECTION, OWNER etc.) # mv /tmp/mail /usr/bin/mail # chown root mail # chgrp kmem mail # chmod 6755 mail ------------------------------------------------------------------------------- End of Digital Equipment Corporation Document. =============================================================================== ------------------------------------------------------------------------------- The CERT/CC would like to thank Tsutomu Shimomura for his assistance and Digital Equipment Corporation for their response to 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. Downloaded From P-80 International Information Systems 304-744-2253