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Home : Advisories : rpc.ypupdated Vulnerability

Title: rpc.ypupdated Vulnerability
Released by: CERT
Date: 12th December 1995
Printable version: Click here

Hash: SHA1


CERT(*) Advisory CA-95:17

Original issue date: December 12, 1995

Last revised: October 30, 1997 - Updated vendor information for Sun.

              A complete revision history is at the end of this file.

Topic: 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.

We will update this advisory as we receive additional information.

Please check advisory files regularly for updates 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.


        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


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


     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


# /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


/^ypupdated/s/^/#DISABLED# /p

#DISABLED# ypupdated/1 stream rpc/tcp wait root /usr/etc/rpc.ypupdated ypupdated




# /bin/ps -eac | /bin/grep inetd

   193   TS  26 ?        0:04 inetd

# /bin/kill -HUP 193


Appendix A: Vendor 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


Digital Equipment Corporation

- -----------------------------

       OSF/1 on all Digital platforms is not vulnerable.

       Digital ULTRIX platforms are not vulnerable to this problem.

Hewlett-Packard Company

- -----------------------

        HP-UX versions 10.01, 10.10, and 10.20 are vulnerable (versions

        prior to HP-UX 10.01 are not 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.

IBM Corporation

- ---------------

  AIX 3.2


    APAR - IX55360

    PTF  - U440666

    To determine if you have this PTF on your system, run the following


       lslpp -lB U440666

  AIX 4.1


    APAR - IX55363

    To determine if you have this fix on your system, run the following


       lslpp -h | grep -p bos.net.nis.server

    Your version of bos.net.nis.server should be or later.

  To Order


    APARs may be ordered using FixDist or from the IBM Support Center.

    For more information on FixDist reference URL:


    or send e-mail to aixserv@austin.ibm.com with a subject of "FixDist".

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


# 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:


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.


- ---------

        Not vulnerable.

Sun Microsystems, Inc.

- ----------------------

BUG 1230027/1232146   fixed in 4.1.3, will not fix 2.4

The ypupdated program is no longer shipped with NS-KIT. If we do

decide in the future to support it again, we will fix the bug.

- -----------------------------------------------------------------------------

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


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, 1996 Carnegie Mellon University. Conditions for use,

disclaimers, and sponsorship information can be found in

http://www.cert.org/legal_stuff.html and http://ftp.cert.org/pub/legal_stuff .

If you do not have FTP or web access, send mail to cert@cert.org with

"copyright" in the subject line.

CERT is registered in the U.S. Patent and Trademark Office.


Revision history

Oct. 30, 1997  Updated vendor information for Sun.

Sep. 23, 1997  Updated copyright information

Aug. 30, 1996  Information previously in the README was inserted

               into the advisory.

Feb. 21, 1996  Appendix, IBM - added an entry for IBM

Dec. 18, 1995  Appendix, Digital & Hewlett-Packard - modified information


Version: PGP for Personal Privacy 5.0

Charset: noconv





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