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CA-94:09                         CERT Advisory
                                 May 23, 1994
                            /bin/login Vulnerability
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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 containing the
CA-94:09.README, which lists the vendors who have responded to our
inquiries, and the status of their investigation into this
vulnerability report.  As we receive additional information relating
to this advisory, we will place it, along with any clarifications, in
the README file, available via anonymous FTP from info.cert.org.  We 
encourage you to check the README files regularly for updates on
advisories that relate to your site.  

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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 patch that addresses the remote access problem has been made
     available via anonymous FTP from sunsite.unc.edu: 

          /pub/Linux/system/Network/sunacm/URGENT/README.security
          /pub/Linux/system/Network/sunacm/URGENT/security.tgz

     The "security.tgz" file includes other security fixes in addition
     to the /bin/login patch. 

     Checksum information for README.security:
          BSD:      09575     1
          SystemV:  20945 1 README.security
          MD5:      MD5 (README.security) = 41d14d7b8725c7a1015adeb49601619b

     Checksum information for security.tgz:
          BSD:      32878   257
          SystemV:  40797 513 security.tgz
          MD5:      MD5 (security.tgz) = dd4585cf4da1b52d25d619bf45f55b75

     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.  As we receive
     additional information, we will update the CA-94:09.README file.
     Again, we encourage you to check this README file regularly for
     updates.

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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.
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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 and their associated README files, information about
FIRST representatives, and other information related to computer
security are available for anonymous  FTP from info.cert.org. 


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Appendix

CA-94:09.README

This file is a supplement to the CERT Advisory
CA-94:09.bin.login.vulnerability of May 23, 1994, and will be updated
as additional information becomes available. 

We have received feedback from these vendors, who indicated that their
products are not vulnerable: 

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

CERT has verified that the following vendor products are not vulnerable:

     Free BSD 

We have received feedback from these vendors, who have made patches
available to address the /bin/login vulnerability:

     IBM
       workaround:       see Section III. Solution for IBM AIX
                         vulnerability A. Workaround of CERT advisory
                         CA-94:09.bin.login.vulnerability
       emergency patch:  software.watson.ibm.com:/pub/rlogin/rlogin.tar.Z
       Official patch:   APAR IX44254

     Linux  
       patch:  sunsite.unc.edu:/pub/Linux/system/Network/sunacm/URGENT/*


