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TUCoPS :: Unix :: General :: ciacg033.txt

Rdist Vulnerability



                       The U.S. Department of Energy
                    Computer Incident Advisory Capability
                           ___  __ __    _     ___
                          /       |     /_\   /
                          \___  __|__  /   \  \___

                             INFORMATION BULLETIN

                              rdist vulnerability

July 24, 1996 17:00 GMT                                            Number G-33
PROBLEM:       A new vulnerability has been discovered in the rdist program,
               and an exploit script is being widely distributed for this
PLATFORM:      Any UNIX system with an unpatched rdist that is set-uid to root.
DAMAGE:        This vulnerability can allow an unprivileged local user to gain
               root access.
SOLUTION:      Apply the patches listed in the Vendor section of the bulletin
VULNERABILITY  This vulnerability is widely known, and exploit scripts are
ASSESSMENT:    being distributed over the Internet. It is highly recommended
               that you apply these patches as soon as possible.

[ Begin CERT Bulletin ]

CERT(sm) Advisory CA-96.14
July 24, 1996

Topic: Vulnerability in rdist

This advisory supersedes CA-91:20.rdist.vulnerability and

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

The CERT Coordination Center has received reports that a new vulnerability
in rdist has been found and an exploitation script is widely available.
Current reports indicate that the script works on x86-based versions of the
UNIX Operating System; however, we believe that it would not be difficult to
write variants that work on other instruction sets and configurations.

The CERT/CC Staff recommends following the steps in Section III.A. to
determine if your system is vulnerable and to disable vulnerable programs,
then following your vendor's instructions (Section III.B and Appendix A).
Until you can install a vendor patch, you may want to install a freely
available version of rdist, noted in Section III.C.

As we receive additional information relating to this advisory, we
will place it in

We encourage you to check our README files regularly for updates on
advisories that relate to your site.

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

I.   Description

     The rdist program is a UNIX Operating System utility used to distribute
     files from one host to another. On most systems, rdist is installed as
     set-user-id root, a necessity due to its design. Unfortunately, this
     setting makes it a favorite target for vulnerability investigation.

     A new vulnerability in rdist has been discovered and reported. The
     vulnerability lies in the lookup() subroutine where the value of a
     command line argument is used to overflow the subroutine call stack.
     If that argument is specially crafted with native machine code,
     lookup() returns control to the code added to the call stack instead of
     the subroutine that called lookup(). If, for example, this added code
     uses a member of the exec system call family and names /bin/sh as the
     program to be executed, that shell is then run with set-user-id root
     privileges. No matter what code is added, the code runs with
     set-user-id root privileges.

     An exploitation program, which is circulating on the Internet, takes
     advantage of this vulnerability. While it purports to work only on
     x86-based versions of the UNIX Operating System, variants tuned to other
     instruction sets and configurations are straightforward to write.

II.  Impact

     On unpatched systems, anyone with access to a local account can gain root

III. Solution

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

     If you need the functionality that rdist provides, install a vendor
     patch (Sec. B). Until you can do so, you may want to install 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 (Sec. C).

     A. How to determine if your system is vulnerable

        To determine if a system is vulnerable and to disable the programs
        that are believed to be 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 two lines using a back-slash.

             find FILE_SYSTEM_NAMES -xdev -type f -user root \
                    -name rdist -perm -04000 -print -ok chmod u-s '{}' \;

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

        Once found, those files will
            - have their names printed (-print)
            - have the setuid mode removed, but only if you type `y'
              in response to the prompt (-ok chown u-s '{}' \;)

     B. Obtain and install the appropriate patch

        Below is a list of the vendors who have reported to us as of
        the date of this advisory. Details are in Appendix A.

            Berkeley Software Design, Inc.
            Data General Corporation
            FreeBSD, Inc.
            Hewlett-Packard Company
            IBM Corporation
            NEC Corporation
            The Santa Cruz Operation
            Sequent Computer Systems
            Silicon Graphics, Inc.
            Sun Microsystems, Inc.

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

        Appendix A is reproduced in CA-96.14.README, which will be updated as
        we receive additional information.

     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 strongly 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.

         For versions of rdist V6 prior to 6.1.3: If you compile rdist with
         -DDIRECT_RCMD *and* you run rdist setuid to root, you are vulnerable
         to the problem described in this advisory. You need to update to
         rdist version 6.1.3.

         Note that by default, rdist V6 is distributed to compile without
         -DDIRECT_RCMD and not run setuid to root. If you have previously
         built version 6.X of rdist with the -DDIRECT_RCMD directive added to
         the $(DEFS_LOCAL) and set "RDIST_MODE = 4555" in "Makefile.local", we
         recommend that you first disable this version with the find command
         given in Section III.A above, then either rebuild rdist with its
         default settings or upgrade to 6.1.3.

- - ---------------------------------------------------------------------------
The CERT Coordination Center staff thanks Michael Cooper
(Michael.Cooper@Sun.Com) for his work on resolving this problem. He is the
maintainer of the publicly available version of rdist.
- - ---------------------------------------------------------------------------

Copyright 1996 Carnegie Mellon University
This material may be reproduced and distributed without permission provided
it is used for noncommercial purposes and the copyright statement is

CERT is a service mark of Carnegie Mellon University.

This file:
               click on "CERT Advisories"
Appendix A: Vendor Information

Current as of July 24, 1996
See CA-96.14.README for updated information.

Below is information we have received from vendors concerning the
vulnerability described in this advisory. If you do not see your vendor's
name, please contact the vendor directly for information.

Berkeley Software Design, Inc.
        BSD/OS is vulnerable to this problem.

        BSDI has released a patch for rdist in BSD/OS V2.1.

        Sites using the non-kerberized rdist should install patch
        U210-018, which is available from the
        mailback server and also from:


        md5 checksum: 86005d8bbb67eb737120741bd254d26a U210-018

        Domestic licensees that are using the Kerberos package
        should install patch D210-018 from the
        mailback server (this patch is available only to domestic
        licensees because of US export restrictions on crypto
        software). Be sure to install only the appropriate patch.

        md5 checksum: b2060ec4eb9b18ace4e76bcb9441353f D210-018

Data General Corporation
        Data General does not provide a version of rdist as part of the
        standard release of DG/UX. Rdist is available as contributed
        software which is not supported by Data General. This problem will
        be fixed in the next release of the contributed software package.

FreeBSD, Inc.
        Versions affected:
                FreeBSD 2.0, 2.0.5, 2.1, 2.1-stable, and 2.2-current
        Versions corrected:
                2.1-stable and 2.2-current as of 1996-07-11
                As root, execute the commands:

                        # chflags noschg /usr/bin/rdist
                        # chmod u-s,go-rx /usr/bin/rdist


        For more information:

Hewlett-Packard Company
        HP/UX 10.X is vulnerable, 9.X is not vulnerable.
        Patches are in process.

IBM Corporation
   AIX is vulnerable to this problem. Fixes are in process but are
   not yet available. The APAR numbers for the fixes are given below.
   In the meantime, we recommend removing the setuid bit from the
   /usr/bin/rdist program.

  To remove the setuid bit, follow these instructions.

     As the root user, type:

        chmod u-s /usr/bin/rdist

  AIX 3.2
    Apply the following fix to your system:

        APAR - IX59741

  AIX 4.1
    Apply the following fix to your system:

        APAR - IX59742

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

       instfix -ik IX59742

  AIX 4.2
    Apply the following fix to your system:

        APAR - IX59743

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

       instfix -ik IX59743

  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 with a subject of "FixDist".

  IBM and AIX are registered trademarks of International Business Machines

        Almost all Linux distributions ship with rdist non setuid.
        If you have changed your rdist to run setuid you are probably

NEC Corporation
        EWS-UX/V(Rel4.2)     not vulnerable

        EWS-UX/V(Rel4.2MP)   not vulnerable

        UP-UX/V(Rel4.2MP)    not vulnerable

        UX/4800              not vulnerable

The Santa Cruz Operation
The following releases of SCO Software are known to contain a version of
rdist that is vulnerable:

SCO OpenServer 5.0.2, 5.0.0
SCO Internet FastStart 1.0

SCO Open Server Enterprise/Network System 2.0, 3.0
SCO Open Desktop 2.0, 3.0
SCO Open Desktop Lite 3.0

SCO UnixWare 2.0, 2.1

SCO TCP/IP 1.2.0, 1.2.1

Patches are being developed for the following releases:

SCO OpenServer 5.0.2, 5.0.0
SCO Internet FastStart 1.0
SCO UnixWare 2.1

Sequent Computer Systems
        Sequent systems do not ship with rdist.

Silicon Graphics, Inc.
        All SGI IRIX versions of rdist are not vulnerable.
        No action is required.

Sun Microsystems, Inc.

The following patches correct the rdist vulnerability (Sun bug id 1258139),
described in this advisory, on systems running Solaris 1.x or 2.x.

Architecture   SunOS    Solaris   Patch     MD5 checksum for rdist binary
- - ---------------------------------------------------------------------------
SPARC          4.1.3     1.1    100383-07  5F2C2B782881FE18D2737B5FA0AEC489
               4.1.3_U1  1.1.1  103823-01  B330358F4E66CD544B9B60AF453C5F2B
               4.1.4     1.1.2  103824-01  11BDEC384048CD42200BC1D0F25B61C9
               5.3       2.3    101494-02  1DD34E9E7C50B2C863E30D67DFD1A905
               5.4       2.4    103813-01  90DD81A4C32F7D583737F171B821386B
               5.5       2.5    103815-01  C3BBE3F6758B0BBA7D45CB05009ED80E
               5.5.1     2.5.1  103817-01  89735351119896FEB7469DCA76788561

X86            5.4       2.4    103814-01  EE4509D9CF87DBD29ABB7A72C8330F89
               5.5       2.5    103816-01  3363670F316A06803ECCDD9FFAE95126
               5.5.1     2.5.1  103818-01  8C2E8CFDE7A2AE6D5EC89139D592E71C

PowerPC        5.5.1     2.5.1  103819-01  C3FC0E54B23E4209496A4735D09DFFEF

These patches will be available through your local SunService and SunSoft
Support Services organizations by 9:00 PDT Wednesday, July 24. They will
also be available at the same time from SunSolve Online, via the URL

CIAC wishes to acknowledge the contributions of CERT for the
information contained in this bulletin.

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