============================================================================= CA-94:06 CERT Advisory March 21, 1994 Writable /etc/utmp Vulnerability ============================================================================= The CERT Coordination Center has received information concerning a vulnerability that exists on systems where the file /etc/utmp is writable by any user on the system. This vulnerability is being actively exploited; please review CERT Advisory CA-94:01 "Ongoing Network Monitoring Attacks." The problem is known to affect Sun Microsystems, Inc. SunOS 4.1.X and Solaris 1.1.1 operating systems. Solbourne Computer, Inc. and other Sparc products using SunOS 4.1.X or Solaris 1.1.1 are also affected. Solaris 2.x is not affected by this problem. Patches can be obtained from Sun Answer Centers worldwide. They are also available via anonymous FTP from ftp.uu.net in the /systems/sun/sun-dist directory, and in Europe from ftp.eu.net in the /sun/fixes directory. CERT queried several vendors in addition to Sun. The following vendors reported that their operating systems, as distributed by the vendor, are not affected by this problem: Convex Computer Corporation Digital Equipment Corporation Data General Corporation Hewlett-Packard Company IBM Intergraph Motorola, Inc. NeXT, Inc. Pyramid Technology Corporation Sequent Computer Systems Sony Corporation Currently, we are not aware of /etc/utmp being writable on other systems. If your operating system is not explicitly mentioned above, and if you determine that /etc/utmp is writable by someone other than root, we encourage you to contact your vendor. If /etc/utmp on your system is writable only by the root account, you need not be concerned about the vulnerability. CERT recommends that sites check their /etc/utmp file to be sure it is not writable by users other than root. If it is generally writable, you should obtain patches from the system vendor or protect /etc/utmp as described below. ----------------------------------------------------------------------------- I. Description If the file /etc/utmp is writable by users other than root, programs that trust the information stored in that file can be subverted. II. Impact This vulnerability allows anyone with access to a user account to gain root access. III. Solution The solutions to this vulnerability are to either (a) protect the file, or (b) patch all the programs that trust it. A. To protect the file, make /etc/utmp writable only by root: # chown root /etc/utmp # chmod 644 /etc/utmp B. Patches from Sun Microsystems Program Patch ID Patch File Name ------- --------- --------------- in.comsat 100272-07 100272-07.tar.Z dump 100593-03 100593-03.tar.Z syslogd 100909-02 100909-02.tar.Z in.talkd 101480-01 101480-01.tar.Z shutdown 101481-01 101481-01.tar.Z write 101482-01 101482-01.tar.Z Program BSD SVR4 MD5 Digital Signature Checksum Checksum ------- --------- --------- -------------------------------- in.comsat 26553 39 64651 78 912ff4a0cc8d16a10eecbd7be102d45c dump 52095 242 41650 484 cdba530226e8735fae2bd9bcbfa47dd0 syslogd 61539 108 38239 216 b5f70772384a3e58678c9c1f52d81190 in.talkd 47917 44 32598 88 5c3dfd6f90f739100cfa4aa4c97f01df shutdown 46562 80 56079 159 bfc257ec795d05646ffa733d1c03855b write 61148 41 48636 81 f93276529aa9fc25b35679ebf00b2d6f --------------------------------------------------------------------------- If you believe that your system has been compromised, contact the CERT Coordination Center or your representative in Forum of Incident Response and Security Teams (FIRST). Internet E-mail: cert@cert.org Telephone: 412-268-7090 (24-hour hotline) CERT personnel answer 8:30 a.m.-5:00 p.m. EST(GMT-5)/EDT(GMT-4), and are on call for emergencies during other hours. CERT Coordination Center Software Engineering Institute Carnegie Mellon University Pittsburgh, PA 15213-3890 Past advisories, information about FIRST representatives, and other information related to computer security are available for anonymous FTP from info.cert.org.