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CERT(sm) Advisory CA-94:09
Original issue date:  May 23, 1994
Last revised: August 30, 1996
              Information previously in the README was inserted into the
              advisory.

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

Topic: /bin/login Vulnerability
- -----------------------------------------------------------------------------

The CERT Coordination Center has learned of a vulnerability in
/bin/login.  This vulnerability potentially affects all IBM AIX 3
systems and Linux systems.  At this time, we believe that only
IBM AIX 3 and Linux systems are at risk.

Included with this advisory is an appendix that lists the vendors who have
responded to our inquiries, and the status of their investigation into this
vulnerability report.  We will update this advisory as we receive additional
information.

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

I.   Description of IBM AIX vulnerability

    A vulnerability exists in /bin/login on all IBM AIX 3 systems.

II.  Impact of IBM AIX vulnerability

    Remote users can obtain unauthorized root access on the affected
    hosts.

III. Solution for IBM AIX vulnerability

    IBM is working on an official fix, which is still under
    development.  The reference number for this fix is APAR IX44254.
    Until you obtain the official fix from IBM, we encourage you to
    apply the workaround or install the emergency fix below.

       A. Workaround

          The recommended workaround is to disable the rlogin daemon:

          1. As root, edit /etc/inetd.conf
             Comment out the line 'login ... rlogin'
          2. Run 'inetimp'
          3. Run 'refresh -s inetd'

       B. Emergency fix

          The emergency fix for the different levels of AIX 3
          affected by this vulnerability is available via anonymous
          FTP from software.watson.ibm.com:/pub/rlogin/rlogin.tar.Z.
          Installation instructions are included in the README file
          (which is included in rlogin.tar.Z).

          Checksum information for rlogin.tar.Z:
             BSD:      25285   317
             SystemV:  13021 633 rlogin.tar.Z
             MD5:      MD5 (rlogin.tar.Z) = 803ee38c2e3b8c8c575e2ff5e921034c

       C. Official fix

          The official fix for this problem can be ordered as
          APAR IX44254.

          To order an APAR from IBM in the U.S., call 1-800-237-5511
          and ask IBM to ship it as soon as it is available.
          According to IBM, this fix will be available in
          approximately two weeks.  APARs may be obtained outside the
          U.S. by contacting your local IBM representative.


IV.  Description of Linux vulnerability

    A vulnerability exists in /bin/login for Linux systems.

V.   Impact of Linux vulnerability

    Any user, remote or local, can obtain unauthorized root access on
    the affected hosts.

VI.  Solution for Linux vulnerability

    A set of tools has been released by Florian La Roche <[email protected]>
    under the name "NetKit."  It is available via the FTP sites listed below.
    An excerpt from the README provides the following general information:

     This directory contains a collection of net source programs for LINUX.

     NetKit-A  A is the first character in the alphabet -> basic things
               contains a collection of LINUX-specific programs and
               several small utility programs found somewhere in the
               Internet or on News
               (contains also net-032 from Alan Cox)
     NetKit-B  B like BSD, even if we only think about LINUX
               contains source code derived from NetBSD
     NetKit-M  M like mail
               contains context diffs and some source code to make a
               good mail system
     NetKit-N  N like news
               contains context diffs for a good News system
               (news readers and also INN for your own newsfeed)
     NetKit-X  X like eXtra
               will maybe be necessary, if NetKit-A grows too large


    sunacm.swan.ac.uk:/pub/misc/Linux/Networking/PROGRAMS/Packages
    ------------------------------------------------------------------------
    MD5 (NetKit-A-0.05.bin.tar.gz) = afe45e04f359b0ff99e66cc58b4e758c
    MD5 (NetKit-A-0.05.tar.gz) = a17fae1b58e1cf8a79aef30296f65672
    MD5 (NetKit-A-0.06.bin.tar.gz) = e0f813427341b070ab9f8374ad721134
    MD5 (NetKit-A-0.06.tar.gz) = adb00607cb2887c44f5aa8981fb8120b
    MD5 (NetKit-B-0.04.bin.tar.gz) = ffe7099a0271a85eb22c78f7c3373bc6
    MD5 (NetKit-B-0.04.tar.gz) = 156be1d3571b1681485b47255f7e202c
    MD5 (NetKit-B-0.05.bin.tar.gz) = 3b270017ce28328c5596291e6d2687f0
    MD5 (NetKit-B-0.05.tar.gz) = ba2327f741a265edc252e86b442a0a0d
    MD5 (NetKit-M-0.01.tar.gz) = 392cbe6454965ad0d9e12f98af4cdd4a
    MD5 (NetKit-N-0.01.tar.gz) = 55957726205a52621a15938c3bea593b

    sunsite.unc.edu:/pub/Linux/system/Network/sunacm
    ------------------------------------------------------------------------
    MD5 (NetKit-A-0.05.bin.tar.gz) = afe45e04f359b0ff99e66cc58b4e758c
    MD5 (NetKit-A-0.05.tar.gz) = a17fae1b58e1cf8a79aef30296f65672
    MD5 (NetKit-A-0.06.bin.tar.gz) = e0f813427341b070ab9f8374ad721134
    MD5 (NetKit-A-0.06.tar.gz) = adb00607cb2887c44f5aa8981fb8120b
    MD5 (NetKit-B-0.04.bin.tar.gz) = ffe7099a0271a85eb22c78f7c3373bc6
    MD5 (NetKit-B-0.04.tar.gz) = 156be1d3571b1681485b47255f7e202c
    MD5 (NetKit-B-0.05.bin.tar.gz) = 3b270017ce28328c5596291e6d2687f0
    MD5 (NetKit-B-0.05.tar.gz) = ba2327f741a265edc252e86b442a0a0d
    MD5 (NetKit-M-0.01.tar.gz) = 392cbe6454965ad0d9e12f98af4cdd4a
    MD5 (NetKit-N-0.01.tar.gz) = 55957726205a52621a15938c3bea593b

    To address the local access problem, we encourage you to install
    a version of /bin/login that does not allow the -f option in the
    form "-f<user>", but only allows this option in the form
    "-f <user>", as two arguments.  At this time, we do not know
    which versions of login.c are vulnerable.


............................................................................

Appendix

We have received feedback from the following, who indicated that their
products are not vulnerable:

    Amdahl
    Apple
    BSD
    BSDI
    FreeBSD
    Harris
    HP
    Linux
    Motorola
    NeXT
    Pyramid
    SCO
    Sequent
    SGI
    Solbourne
    Sony
    Sun


CERT has received feedback from the following vendors, who have made
patches available to address the /bin/login vulnerability.  Please
note that vendors sometimes update patch files.  If you find that the
checksum is different, please contact the vendor.


 IBM - Please see Sec. III, "Solution for IBM AIX vulnerability" for details.
       Briefly--
     Official patch: APAR IX44254.
     Emergency fix:  Available via anonymous FTP from:
                     software.watson.ibm.com:/pub/rlogin

                     This directory contains the latest available emergency
                     fix for APAR IX44254.  As updates become available,
                     any new versions will be placed in this directory with
                     the name rlogin<#>.tar.Z with <#> being incremented
                     for each update.  See the README.FIRST file in that
                     directory for details.

LINUX: - Please see Sec. VI, "Solution for Linux vulnerability" for details.
        Briefly--
        "Netkit" is available from
        sunacm.swan.ac.uk:/pub/misc/Linux/Networking/PROGRAMS/Packages
        sunsite.unc.edu:/pub/Linux/system/Network/sunacm


- ---------------------------------------------------------------------------
The CERT Coordination Center wishes to thank Axel Clauberg of
University of Cologne for reporting the IBM AIX problem, and
IBM for their assistance in responding to this problem.
- ---------------------------------------------------------------------------

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).

If you wish to send sensitive incident or vulnerability information to
CERT via electronic mail, CERT strongly advises that the e-mail be
encrypted.  CERT can support a shared DES key, PGP (public key
available via anonymous FTP on info.cert.org), or PEM (contact CERT
for details).

Internet E-mail: [email protected]
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
USA

Past advisories, information about FIRST representatives, and other
information related to computer security are available for anonymous FTP from
info.cert.org.

Copyright 1994, 1995, 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
included.

CERT is a service mark of Carnegie Mellon University.

===========================================================================
UPDATES

We are aware that there have been several /bin/login wrapper
programs posted as proposed workarounds for this vulnerability.  None
of the wrappers that CERT has reviewed have fully addressed all
aspects of this vulnerability.  CERT will not undertake any further
review of such wrappers.  Instead, we encourage sites to apply the
appropriate workaround or patches available, as described in
CA-94:09.bin.login.vulnerability.

Frequently Asked Question about this CERT advisory:

   Question:  Why is rshd not mentioned in this advisory?
   Answer:    From the man page for RSH(1C):

                   rsh hostname [ -l username ] [ -n ] [ command ]

                   rsh connects to the specified hostname and
                   executes the specified command.
                   If you omit [ command ], instead of executing a
                   single command, rsh logs you in on the remote host
                   using rlogin(1C).

                      rsh hostname [ -l username ] [ -n ]

              Exploitation of the vulnerability via rsh requires the
              use of rlogind, which then invokes /bin/login.
              Exploitation of this vulnerability by this method is
              addressed by this advisory.

              CERT/CC are not aware of any exploitation method for this
              vulnerability via the following usage:

                      rsh hostname [ -l username ] [ -n ] command


~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Revision history

Aug. 30, 1996  Information previously in the README was inserted into the
              advisory. The result is a major update to patch information in
              Sections III and VI.
Mar. 29, 1996  Updates section - Removed duplicate information from the
              "Frequently Asked Question" section
Feb. 02, 1995  Section III - Updated Linux patch information
May  27, 1994  Updates section - Included caveat concerning other /bin/login
              wrapper programs and comments about rshd


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