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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 <flla@stud.uni-sb.de>
     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: cert@cert.org
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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