============================================================================= CA-95:17 CERT Advisory December 12, 1995 rpc.ypupdated Vulnerability ----------------------------------------------------------------------------- The CERT Coordination Center has received reports of a vulnerability in the rpc.ypupdated program. An exploitation program has also been posted to several newsgroups. This vulnerability allows remote users to execute arbitrary programs on machines that provide Network Information Service (NIS) master and slave services. Client machines of an NIS master or slave server are not affected. See Section III for a test to help you determine if you are vulnerable, along with a workaround. In addition, Appendix A contains a list of vendors who have reported their status regarding this vulnerability. As we receive additional information relating to this advisory, we will place it in: ftp://info.cert.org/pub/cert_advisories/CA-95:17.README We encourage you to check our README files regularly for updates on advisories that relate to your site. ----------------------------------------------------------------------------- I. Description The rpc.ypupdated program is a server used to change NIS information from a network-based client using various methods of authentication. Note: The Network Information Service (NIS) was formerly known as Sun Yellow Pages (YP). The functionality of the two remains the same; only the name has changed. The name Yellow Pages is a registered trademark in the United Kingdom of British Telecommunications plc, and may not be used without permission. Clients connect to rpc.ypupdated and provide authentication information and proposed changes to an NIS database. If authenticated, the information provided is used to update the selected NIS database. The protocol used when clients communicate with a server only checks to see if the connection is authentic using secure RPC. The protocol does not check to see if the client is authorized to modify the NIS data or if the given NIS map exists. Even after an unsuccessful attempt to update the NIS information, the rpc.ypupdated server invokes the make(1) program to propagate possible changes. The invocation of make is implemented in an insecure fashion which allows the requesting client to pass malicious arguments to the call resulting in the execution of arbitrary commands on NIS master and slave servers. II. Impact Remote users can execute commands on vulnerable NIS master and slave machines. III. Solution First determine if you are vulnerable (see Sec. A below). If you are vulnerable, either follow the instructions vendors have provided in Appendix A or apply the workaround in Sec. B below. A. Consult the vendor information in Appendix A. If your vendor is not listed, then check to see if your system has an rpc.ypupdated server. To do this check, consult your system documentation or look in your system initialization files (e.g., /etc/rc*, /etc/init.d/*, and inetd.conf) for rpc.ypupdated or ypupdated. If you find a reference to this program on your system, then it is likely that you are vulnerable. B. Until patches are available for vulnerable systems, we recommend that you disable rpc.ypupdated as soon as possible. Below are some examples given for reference only. Consult your system documentation for the exact details. In these examples, the rpc.ypupdated program is killed if it is running, and the system is reconfigured so that the daemon does not automatically start again when the system is rebooted. Example 1 - SunOS 4.1.X For SunOS 4.1.X master and slave NIS servers, the rpc.ypupdated program is started by the /etc/rc.local script. First, determine if the server is running, and kill it if it is. Then, rename rpc.ypupdated so that the /etc/rc.local script will not find and therefore start it when the system reboots. # /bin/uname -a SunOS test-sun 4.1.4 1 sun4m # /bin/ps axc | /bin/grep rpc.ypupdated 108 ? IW 0:00 rpc.ypupdated # /bin/kill 108 # /bin/ps axc | /bin/grep rpc.ypupdated # /bin/grep ypupdated /etc/rc /etc/rc.local /etc/rc.local: if [ -f /usr/etc/rpc.ypupdated -a -d /var/yp/$dname ]; then /etc/rc.local: rpc.ypupdated; echo -n ' ypupdated' # /bin/mv /usr/etc/rpc.ypupdated /usr/etc/rpc.ypupdated.CA-95:17 # /bin/chmod 0 /usr/etc/rpc.ypupdated.CA-95:17 Example 2 - IRIX On IRIX systems, ypupdated is started by the inetd daemon. For versions 3.X, 4.X, 5.0.X, 5.1.X, and 5.2, the ypupdated is enabled; but for versions 5.3, 6.0.X, and 6.1, it is disabled. Note that the byte counts given for /bin/ed may vary from system to system. Note also that the inetd.conf file is found in different locations for different releases of IRIX. For 3.X and 4.X, it is located in /usr/etc/inetd.conf. For all other releases (5.0.X, 5.1.X, 5.2, 5.3, 6.0.X, and 6.1) it is in /etc/inetd.conf. # /bin/uname -a IRIX test-iris 5.2 02282015 IP20 mips # /bin/grep ypupdated /etc/inetd.conf ypupdated/1 stream rpc/tcp wait root /usr/etc/rpc.ypupdated ypupdated # /bin/ps -eaf | /bin/grep rpc.ypupdated root 184 1 0 Nov 20 ? 0:00 /usr/etc/rpc.ypupdated root 14694 14610 2 11:30:07 pts/3 0:00 grep -i rpc.ypupdated # /bin/kill 184 # /bin/ed /etc/inetd.conf 3344 /^ypupdated/s/^/#DISABLED# /p #DISABLED# ypupdated/1 stream rpc/tcp wait root /usr/etc/rpc.ypupdated ypupdated w 3355 q # /bin/ps -eac | /bin/grep inetd 193 TS 26 ? 0:04 inetd # /bin/kill -HUP 193 --------------------------------------------------------------------------- If you believe that your system has been compromised, contact the CERT Coordination Center or your representative in the Forum of Incident Response and Security Teams (FIRST). If you wish to send sensitive incident or vulnerability information to CERT staff by electronic mail, we strongly advise that the email be encrypted. The CERT Coordination Center can support a shared DES key, PGP (public key available via anonymous FTP on info.cert.org), or PEM (contact CERT staff for details). Internet email: cert@cert.org Telephone: +1 412-268-7090 (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. Fax: +1 412-268-6989 Postal address: CERT Coordination Center Software Engineering Institute Carnegie Mellon University Pittsburgh, PA 15213-3890 USA CERT advisories and bulletins are posted on the USENET newsgroup comp.security.announce. If you would like to have future advisories and bulletins mailed to you or to a mail exploder at your site, please send mail to cert-advisory-request@cert.org. Past CERT publications, information about FIRST representatives, and other information related to computer security are available for anonymous FTP from info.cert.org. Copyright 1995 Carnegie Mellon University This material may be reproduced and distributed without permission provided it is used for non-commercial purposes and the copyright statement is included. CERT is a service mark of Carnegie Mellon University. .............................................................................. Appendix A: Vendor Information Current as of December 12, 1995 See CA-95.17.README for updated information Below is information we have received from vendors. If you do not see your vendor's name below, please contact the vendor directly for information. Apple Computer, Inc. ------------------- A/UX does not include this functionality and is therefore not vulnerable. Berkeley Software Design, Inc. (BSDI) ------------------------------------- BSD/OS by Berkeley Software Design, Inc. (BSDI) is not vulnerable. Data General Corporation ------------------------ Data General believes the DG/UX operating system to be NOT vulnerable. This includes all supported release, DG/UX 5.4 Release 3.10, DG/UX Release 4.10 and all related Trusted DG/UX releases. Digital Equipment Corporation ----------------------------- OSF/1 on all Digital platforms is not vulnerable. Analysis of ULTRIX is under way, and information will be available soon. Hewlett-Packard Company ----------------------- HP-UX versions 1.01, 10.10, and 10.20 are vulnerable. Solution: Do not run rpc.ypupdated. rpc.ypupdated is used when adding or modifying the public:private key pair in the NIS map public key.byname via the chkey command interface. rpc.ypupdated should ONLY be run while changes are being made, then terminated when the changes are complete. Make sure you re-kill rpc.ypupdated after each reboot. NEC Corporation --------------- OS Version Status ------------------ ------------ -------------------------- EWS-UX/V(Rel4.0) R1.x - R2.x not vulnerable R3.x - R6.x vulnerable EWS-UX/V(Rel4.2) R7.x - R10.x vulnerable EWS-UX/V(Rel4.2MP) R10.x vulnerable UP-UX/V R2.x not vulnerable R3.x - R4.x vulnerable UP-UX/V(Rel4.2MP) R5.x - R7.x vulnerable UX/4800 R11.x vulnerable --------------------------------------------------------------- The following is a workaround for 48 series. ypupdated program is started by the /etc/rc2.d/S75rpc script. First, determine if the server is running, killing it if it is. Then, rename ypupdated so that the /etc/rc2.d/S75rpc script will not find and therefore start it when the system reboots. # uname -a UNIX_System_V testux 4.2 1 R4000 r4000 # /sbin/ps -ef | /usr/bin/grep ypupdated root 359 1 0 08:20:05 ? 0:00 /usr/lib/netsvc/yp/ypupdated root 19938 836 0 23:13:20 pts/1 0:00 /usr/bin/grep ypupdated # /usr/bin/kill 359 # /sbin/mv /usr/lib/netsvc/yp/ypupdated /usr/lib/netsvc/yp/ypupdated.CA-95:17 # /usr/bin/chmod 0 /usr/lib/netsvc/yp/ypupdated.CA-95:17 -------------------------- Contacts for further information: E-mail:UX48-security-support@nec.co.jp Open Software Foundation ------------------------ YP/NIS is not part of the OSF/1 Version 1.3 offering. Hence, OSF/1 Version 1.3 is not vulnerable. Sequent Computer Systems ------------------------ Sequent does not support the product referred to in this advisory, and as such is not vulnerable. Silicon Graphics Inc. (SGI) --------------------------- IRIX 3.x, 4.x, 5.0.x, 5.1.x, 5.2: vulnerable. Turn off rpc.ypudated in inetd.conf; it is shipped with this turned on. IRIX 5.3, 6.0, 6.0.1: rpc.ypupdated was off as distributed. Turn off if you have turned it on. Solbourne --------- Not vulnerable. Sun Microsystems, Inc. ---------------------- SunOS 4.1.X is vulnerable. [Note from CERT Coordination Center: We have examined Solaris and found that Solaris 2.x is not shipped with NIS support and the vulnerability is not present. There is an extra software package named the "Solaris Name Service Transition Kit" which in version 1.2, the current version, does not contain the rpc.ypupdated program and is therefore not vulnerable. However, version 1.0 of the Solaris Name Service Transition Kit does contain rpc.ypupdated and is therefore presumed to be vulnerable.]