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TUCoPS :: Unix :: General :: ca-9723.txt

CERT Advisory 97-23 Buffer Overflow Problem in rdist

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CERT* Advisory CA-97.23
Original issue date: September 16, 1997

Last Revised: December 9, 1998
              Updated vendor information for Sun Microsystems, Inc.

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

Topic: Buffer Overflow Problem in rdist
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The CERT Coordination Center has received reports of a vulnerability in rdist
that enables anyone with access to a local account to gain root privileges.
This is not the same vulnerability as the one discussed in CA-96.14.

Section III.A contains instructions on how to determine if your site is
vulnerable. If your implementation of rdist is vulnerable, the CERT/CC team
encourages you to follow your vendor's instructions (Sec. III.B and Appendix
A) or install a freely available version of the rdist program that is not
installed as set-user-id root and is, therefore, not susceptible to the
exploitation described in this advisory (Sec. III.C).

For information on the earlier problem with rdist, see

We will update this advisory as we receive additional information.
Please check our advisory files regularly for updates that relate to your

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

I.   Description

     The rdist program is a UNIX Operating System utility used to
     distribute files from one host to another. On some systems, rdist
     opens network connections using a privileged port as the source port.
     This requires root privileges, and to attain these privileges rdist on
     such systems is installed set-user-id root.

     A new vulnerability has been found in some set-user-id root
     implementations of rdist. The vulnerability lies in the function
     expstr(), where macros supplied as arguments are expanded using
     sprintf(). It is possible to overwrite stack frames and call specially
     pre-crafted native machine code. If the appropriate machine code is
     supplied, an attacker can execute arbitrary programs (such as the
     shell) with set-user-id root privileges.

     Note that this vulnerability is distinct from that discussed in CERT
     advisory CA-96.14.

II.  Impact

     On systems with a vulnerable copy of rdist, anyone with access to a
     local account can gain root access.

III. Solution

     We urge you to follow the steps in Section A to determine if your
     system is vulnerable and, if it is, to turn off rdist while you decide
     how to proceed.

     If your system is vulnerable and you need the functionality that rdist
     provides, you should install a vendor patch (Section B). Until you can
     do so, you may want to use a freely available version of rdist that
     does not need to be installed as set-user-id root and is, therefore,
     not susceptible to the exploitation described in this advisory
     (Section C).

     A. How to check for set-user-id root versions of rdist

        To find set-user-id root versions of rdist and to disable the
        programs that are possibly vulnerable, use the following find
        command or a variant. Consult your local system documentation to
        determine how to tailor the find program on your system.

        You will need to run the find command on each system you maintain
        because the command examines files on the local disk only.
        Substitute the names of your local file systems for
        FILE_SYSTEM_NAMES in the example. Example local file system names
        are /, /usr, and /var. You must do this as root.

        Note that this is one long command, though we have separated
        it onto three lines using backslashes.

             find FILE_SYSTEM_NAMES -xdev -type f -user root \
                    -name '*rdist*' -perm -04000 -exec ls -l '{}' \; \
                    -ok chmod 0500 '{}' \;

        This command will find all files on a system that
            - are only in the file system you name (FILE_SYSTEM_NAMES -xdev)
            - are regular files (-type f)
            - are owned by root (-user root)
            - have "rdist" as a component of the name (-name '*rdist*')
            - are setuid (-perm -04000)

        Once found, those files will
            - have their names and details printed (-exec ls -l '{}')
            - have the setuid mode removed (making the file available
              only to root) but only if you type `y' in response to the
              prompt (-ok chmod 0500 '{}' \;)

     B. Obtain and install the appropriate patch

        Below is a list of vendors who have provided information for this
        advisory. Details are in Appendix A, and we will update the appendix
        as we receive more information.

               Berkeley Software Design, Inc. (BSDI)
               Digital Equipment Corp.
               FreeBSD, Inc.
               Hewlett-Packard Company
               IBM Corporation
               NEC Corporation
               NCR Corporation
               The Santa Cruz Operation, Inc. (SCO)
               Silicon Graphics Inc. (SGI)
               Sun Microsystems, Inc.

        If your vendor's name is not on this list, please contact the
        vendor directly.

     C. If you need the functionality that rdist provides but a patched
        version is not yet available from your vendor, consider installing
        rdist-6.1.3, which is freely available from


              MD5 (rdist-6.1.3.tar.gz) = 8a76b880b023c5e648b7cb77b9608b9f

        The README file in the distribution explains how to configure and
        install this version of rdist.

        We recommend that you configure this version of rdist to use rsh
        instead of rcmd. Here is the relevant text from the README:

            By default rdist uses rsh(1c) to make connections to remote
            hosts. This has the advantage that rdist does not need to be
            setuid to "root". This eliminates most potential security
            holes. It has the disadvantage that it takes slightly more time
            for rdist to connect to a remote host due to the added overhead
            of doing a fork() and then running the rsh(1c) command.

        Some sites with sufficient expertise use the ssh program in
        conjunction with rdist, instead of using rcmd or rsh. If you have
        the expertise, you may want to implement this configuration.

        For further details on this option see "Ssh (Secure Shell) FAQ -
        Frequently asked questions," Section 4.4, "Can I use rdist with ssh?"
        It is available from


        For details on how to obtain ssh, see FAQ Section 3.4, "Where can I
        obtain ssh?" This section can be found in



Appendix A - Vendor Information

Below is a list of the vendors who have provided information for this
advisory. We will update this appendix as we receive additional information.
If you do not see your vendor's name, the CERT/CC did not hear from that
vendor. Please contact the vendor directly.

Berkeley Software Design, Inc. (BSDI)
  BSDI shipped a patch for this for our 2.1 release (U210-018) when
  the original Bugtraq advisory was released.  The 3.0 version of
  rdist is not vulnerable and in fact is no longer even setuid.


  This message is to inform CERT that neither Caldera Network Desktop
  nor Caldera OpenLinux ship rdist SUID and are thus not vulnerable.
  See our advisory on this subject at:

Digital Equipment Corp.
  This reported problem is not present for Digital's ULTRIX or Digital UNIX
  Operating Systems Software.

                                DIGITAL EQUIPMENT CORPORATION

FreeBSD, Inc.
  2.1.0 is vulnerable.
  2.1.5, 2.1.6 and 2.1.7 are and 2.1-stable are not. In any case, upgrading
  to 2.1.7 or even better, 2.1-stable should be considered.
  If there is demand, we'll release a patch for 2.1.0

  All 2.2 releases, 2.2-stable and FreeBSD-current are not vulnerable.

Hewlett-Packard Company
  HP is -not- vulnerable; the problem didn't exist in 9.X, and has been fixed
  in 10.X with Security Bulletin #36 (HPSBUX9608-036) last year.  Patch
  numbers change frequently because of cumulative patching, so please check
  current patch ID information either by bulletin or by platform/release at
  our HP Electronic Support Center in the "Security Patch Matrix," which is
  updated every 24 hours.

 1)  From your Web browser, access the URL: (US,Canada,Asia-Pacific,
       and Latin-America)  (Europe)

 2)  On the HP Electronic Support Center main screen, select the
     hyperlink "Support Information Digests".

 3)  On the "Welcome to HP's Support Information Digests" screen,
     under the heading "Register Now", select the appropriate hyperlink
     "Americas and Asia-Pacific", or "Europe".

 4)  On the "New User Registration" screen, fill in the fields
     for the User Information and Password and then select the button
     labeled "Submit New User".

 5)  On the "User ID Assigned" screen, select the hyperlink
     "Support Information Digests".

  **Note what your assigned user ID and password are for future

 6)  You should now be on the "HP Support Information Digests Main"
     screen.  You might want to verify that your email address is
     correct as displayed on the screen.  From this screen, you may
     also view/subscribe to the digests, including the security
     bulletins digest.

     To get a patch matrix of current HP-UX and BLS security
     patches referenced by either Security Bulletin or Platform/OS,
     click on following screens in order:
        Technical Knowledge Database
        Browse the HP Security Bulletins Archive
        HP-UX Security Patch Matrix

IBM Corporation
  All versions of AIX are vulnerable to this buffer overflow.  There is
  no 3.2 fix.  It is recommended that 3.2 customers upgrade to a higher
  level.  The following APARs will be available for AIX version 4

  AIX 3.2:  upgrade to 4.1.5 or higher
  AIX 4.1:  IX70876
  AIX 4.2:  IX70875

   To Order
    APARs may be ordered using Electronic Fix Distribution (via FixDist)
    or from the IBM Support Center.  For more information on FixDist,
    reference URL:

    or send e-mail to with a subject of "FixDist".

  IBM and AIX are registered trademarks of International Business Machines

NEC Corporation
  The following systems are NOT affected by this vulnerability:


  To report a new vulnerability, contact <>.

NCR Corporation

NCR is delivering a set of operating system dependent patches which
contain an update for this problem .  Accompanying each patch is a
README file which discusses the general purpose of the patch and
describes how to apply it to your system.

Recommended solution:

Apply one of the following patches depending on the revision of the
inet package installed on your system. To check its version execute:

        pkginfo -x inet

For inet 5.01.xx.xx: - PINET501 (Version later than
For inet 6.01.xx.xx: - PINET601 (Version later than
For inet 6.01.xx.xx: - PINET601 (Version later than


  OpenBSD does not have this problem.  None of the versions of rdist
  distributed are setuid or setgid.

The Santa Cruz Operation, Inc. (SCO)
  SCO has determined that the following SCO operating systems are
  not vulnerable:

  - SCO CMW+ 3.0
  - SCO Open Desktop/Open Server 3.0
  - SCO OpenServer 5.0
  - SCO UnixWare 2.1

Siemens-Nixdorf Informationssysteme AG

 Rdist has not been shipped with ReliantUNIX versions prior to 5.43C.
 The latest ReliantUNIX-Y/N version 5.43C contains a vulnerable rdist.

 For this version we recommend to remove the set-user-id root bit from
 /usr/ucb/rdist following the instructions given in section III.A.

 ReliantUNIX-Y/N 5.44A will be shipped with rdist 6.1.3.
 Patches for ReliantUNIX-N/Y 5.43C are available on requirement.
 Please ask SNI's customers service for details."

Silicon Graphics Inc. (SGI)

Silicon Graphics Inc. issued Security Advisory, "IRIX ordist
Buffer Overrun Vulnerability," 19970509-02-PX, August 5, 1997.

Patches are available via anonymous FTP and your service/support provider.

The SGI anonymous FTP site is ( or its
mirror,   Security information and patches can be found
in the ~ftp/security and ~ftp/patches directories, respectfully.

For subscribing to the wiretap mailing list and other SGI security related
information, please refer to the Silicon Graphics Security Headquarters
website located at:


Sun Microsystems, Inc.

Please refer to Sun Microsystems, Inc. Security Bulletin, "rdist," Number:
#00179, distributed November 18, 1998 for additional information relating to
this vulnerability.

Patches and Checksums are available to all Sun customers via World Wide Web at:

Sun security bulletins are available via World Wide Web at:

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

The CERT Coordination Center thanks Hiroshi Nakano of Ryukoku University,
Japan for reporting this problem. We also thank Wolfgang Ley of DFN-CERT
for his assistance with the Solutions section of the advisory.

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

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 (see

CERT/CC Contact Information
- ----------------------------

Phone    +1 412-268-7090 (24-hour hotline)
                CERT personnel answer 8:30-5:00 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

Using encryption
   We strongly urge you to encrypt sensitive information sent by email. We can
   support a shared DES key or PGP. Contact the CERT/CC for more information.
   Location of CERT PGP key

Getting security information
   CERT publications and other security information are available from

   CERT advisories and bulletins are also posted on the USENET newsgroup

   To be added to our mailing list for advisories and bulletins, send
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   In the subject line, type
        SUBSCRIBE  your-email-address

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

Copyright 1997, 1998 Carnegie Mellon University. Conditions for use,
disclaimers, and sponsorship information can be found in and .  If you do not have FTP or web
access, send mail to with "copyright" in the subject

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

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

This file:
               click on "CERT Advisories"

Revision history

Dec. 9, 1998  Updated vendor information for Sun Microsystems, Inc.
May 27, 1998   Updated vendor information for Sun Microsystems.
Jan. 15, 1998  Updated vendor information for NCR.
Nov. 14, 1997  Updated vendor information for Siemens-Nixdorf.
Oct. 3, 1997   Appendix A - added information for Caldera.
Sept. 30, 1997 Updated copyright statement
Sept. 15, 1997 Appendix A - added information for OpenBSD and

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