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Home : Advisories : /bin/login Vulnerability

Title: /bin/login Vulnerability
Released by: CERT
Date: 23rd May 1994
Printable version: Click here

Hash: SHA1


CERT(*) Advisory CA-94:09

Original issue date:  May 23, 1994

Last revised:  March 10, 1998. Updated vendor information for DEC.

               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


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

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


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 

     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



     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



     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", but only allows this option in the form

     "-f ", as two arguments.  At this time, we do not know

     which versions of login.c are vulnerable.



We have received feedback from the following, who indicated that their

products are not vulnerable:





     Digital Equipment Corporation














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.


      Official patch: APAR IX44254.

      Emergency fix:  Available via anonymous FTP from:


                      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.


         "Netkit" is available from



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

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


Past advisories, information about FIRST representatives, and other

information related to computer security are available for anonymous FTP from


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

Copyright 1994, 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.



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


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

Mar. 10, 1998  Updated vendor information for DEC.

Sep. 23, 1997  Updated copyright statement

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


Version: PGP for Personal Privacy 5.0

Charset: noconv





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