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CERT(sm) Advisory CA-95:07a       
Original issue date:  April 21, 1995
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: SATAN Vulnerability: Password Disclosure
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                   *** This is a revised CERT advisory.***
               It addresses inaccurate information in CA-95:07
                 and contains information about SATAN 1.1.1.
                         *** Supersedes CA-95:07 ***

There was a potential vulnerability introduced into systems running SATAN 1.0
and earlier, as described below. The problem has been addressed in version 1.1
and later. The CERT/CC team recommends that you take the precautions described
in Section III below before you run SATAN and that you upgrade to the latest
version of SATAN--currently 1.1.1.

The following two statements from CA-95:07 are inaccurate.

1. This statement is incorrect: "Note that SATAN 1.1 is expected to check
   systems for this SATAN 1.0 vulnerability as part of scanning other
   systems." 

2. This statement is misleading: "This vulnerability affects all systems 
   that support the use of SATAN with the HTML interface."  For SATAN 1.0 
   and earlier, whether a system is vulnerable depends on the system
   configuration, the net browser supporting SATAN, and how SATAN is used.
   The problem has been solved in later versions of SATAN.

We will update this advisory as we receive additional information.
Please check advisory files regularly for updates that relate to your site.

For an overview of a beta version of SATAN, see CERT advisory CA-95:06.

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I.   Description

     In SATAN version 1.0, access to the SATAN processes is protected by a
     session key (also referred to as a "magic cookie" or "password"). SATAN
     itself never sends this session key over the network. However, depending
     on the configuration at your site, the supporting HTML browser, and how
     you use SATAN, your session key may be disclosed through the network.
     Local or remote users who obtain your session key can run perl scripts
     that are on the system running SATAN.    

     If you use SATAN only through the command line interface, your system is
     not vulnerable to the problem because there is no session key.

     Additional details are in the "SATAN Password Disclosure" tutorial
     provided with SATAN. We have included the tutorial as an Appendix B of
     this advisory.  

II.  Impact

     If the session key is disclosed while SATAN 1.0 is running, unauthorized
     local or remote users can execute perl scripts as the user of the process
     running SATAN (typically root).  

III. Solution

     1. Obtain and install SATAN version 1.1.1, which addresses the problem.
        For details on how the problem is addressed, see the section entitled
        "Additional SATAN Defenses" in the SATAN Password Disclosure tutorial.
        The SATAN authors also provide guidance on protecting access; see the
        tutorial section, "Preventing SATAN Password Disclosure."  
        SATAN 1.1.1 is available from many sites, including

             ftp://ftp.win.tue.nl/pub/security/satan-1.1.1.tar.Z
             ftp://ftp.win.tue.nl/pub/security/satan-1.1.1.README
             ftp://ftp.win.tue.nl/pub/security/satan-1.1.1.tar.Z.asc         
    
             MD5 (satan-1.1.1.tar.Z) = de2d3d38196ba6638b5d7f37ca8c54d7
             MD5 (satan-1.1.1.README) = 3f935e595ab85ee28b327237f1d55287
             MD5 (satan-1.1.1.tar.Z.asc) = a9261070885560ec11e6cc1fe0622243

        To locate other sites, you can send mail to
             majordomo@wzv.win.tue.nl

        and put in the body of the message (not the subject line):
             get satan mirror-sites

        There are reports of modified copies of SATAN, so ensure that the copy
        that you obtain is authentic by checking the MD5 checksum or SATAN
        author Wietse Venema's PGP signature. Appendix A of this advisory
        contains his PGP key.

        We urge you to read the SATAN documentation carefully before
        running SATAN.

     2. We also recommend that you take the following precautions:

        * Install all relevant security patches for the system on which you
          will run SATAN. 

        * Execute SATAN only from the console of the system on which it is
          installed (e.g., do not run SATAN from an X terminal, from a
          diskless workstation, or from a remote host). 

        * Ensure that the SATAN directory tree is not NFS-mounted (or AFS,
          etc.) from a remote system. 

        * Ensure that the SATAN directory tree cannot be read by users other
          than root.

        * Do not open any URLs outside your own system and site while
          running the browser started by SATAN. For example, do not use
          previously stored URLs such as those found in bookmarks and
          pull-down menus. 

        *  Do not link to any URLs outside your own system and site while
           running the browser started by SATAN. If you use external links
           while SATAN is running from the SATAN browser, security can be
           compromised on the system from which you are executing SATAN. So,
           for example, do not use previously stored links such as those found
           in bookmarks and pull-down menus. 

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Appendix A: Wietse Venema's PGP Key

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Appendix B: Tutorial - SATAN Password Disclosure

The following tutorial can be found in
    satan-1.1.1/html/tutorials/vulnerability/SATAN_password_disclosure.html

SATAN Password Disclosure

SUMMARY

    SATAN password disclosure via flawed HTML clients or environmental
    problems

IMPACT

    Unauthorized users may execute commands through SATAN

BACKGROUND

    By default, SATAN runs as a custom HTML (hypertext markup language)
    server, executing requests from a user-provided HTML browser, or
    client program.  Examples of common HTML clients are Netscape, NCSA
    Mosaic and Lynx.

    An HTML client request is nothing but a network message, and
    network messages may be sent by any user on the network.  To defend
    itself against requests from unauthorized users, SATAN takes the
    following precautions:

    * SATAN generates a session key, to be used as a secret password,
      each time it starts up an HTML client.  The session key is in the
      form of a 32-byte quasi-random number.  The number is called
      quasi-random because it is impossible to generate real random
      numbers using only software.

    * SATAN creates HTML files with the secret password embedded in URL
      (uniform resource locator) links. The HTML file access
      permissions are restricted to the owner of the SATAN process (and
      the superuser).

    * SATAN rejects HTML requests whose URL does not contain the
      current SATAN password. This requirement prevents access by
      unauthorized clients, provided that the current SATAN password is
      kept secret.

    The protection scheme used by SATAN is in essence the same as the
    scheme used by many implementations of the X Window system: MIT
    magic cookies. These secrets are normally kept in the user's home
    directory, in a file called .Xauthority. Before it is granted
    access to the screen, keyboard and mouse, an X client program needs
    to prove that it is authorized, by handing over the correct magic
    cookie.  This requirement prevents unauthorized access, provided
    that the magic cookie information is kept secret.

THE PROBLEM

    It is important that the current SATAN password is kept secret.
    When the password leaks out, unauthorized users can send commands
    to the SATAN HTML server where the commands will be executed with
    the privileges of the SATAN process.

    Note that SATAN generates a new password every time you start it up
    under an HTML client, so if you are suspicious, simply restart the
    program.

    SATAN never sends its current password over the network. However,
    the password, or parts of it, may be disclosed due to flaws in
    HTML clients or due to weak protection of the environment that
    SATAN is running in.  One possible scenario for disclosure is:

    * When the user selects other HTML servers from within a SATAN
      session, some HTML client programs (Netscape and Lynx) disclose
      the current SATAN URL, including SATAN password information.  The
      intention of this feature is to help service providers find out
      the structure of the world-wide web.  However, the feature can
      also reveal confidential information. With version 1.1 and later,
      SATAN displays a warning when the HTML client program exhibits
      this questionable (i.e. stupid) feature.

    Other scenarios for SATAN password disclosure are discussed in the
    next section, as part of a list of counter measures.

PREVENTING SATAN PASSWORD DISCLOSURE

    The security of SATAN is highly dependent on the security of
    environment that it runs in. In the case of an X Window
    environment:

    * Avoid using the xhost mechanism, but use xauth and MIT magic
      cookies or better. Otherwise, unauthorized users can see and
      manipulate everything that happens with the screen, keyboard and
      mouse.  Of course, this can also be a problem when you are not
      running the SATAN program at all.

    Steps that can help to keep the X magic cookie information secret:

    * Avoid sharing your home directory, including .Xauthority file,
      with other hosts. Otherwise, X magic cookie information may be
      captured from the network while the X software accesses that
      file, so that unauthorized users can take over the screen,
      keyboard and mouse.

    * Avoid running X applications with output to a remote display.
      Otherwise, X magic cookie information can be captured from the
      network while X clients connect to the remote display, so that
      unauthorized users can take over the screen, keyboard and mouse.

    Finally, steps that can help to keep the current SATAN password
    secret:

    * Avoid sharing the SATAN directories with other hosts. Otherwise,
      SATAN password information may be captured from the network while
      the HTML software accesses passworded files, so that unauthorized
      users can take over the SATAN HTML server.

    * Avoid running SATAN with output to a remote display. Otherwise,
      SATAN password information can be captured from the network while
      URL information is shown on the remote display, so that
      unauthorized users can take over the SATAN HTML server.

ADDITIONAL SATAN DEFENSES
   
    The SATAN software spends a lot of effort to protect your computer
    and data against password disclosure. With version 1.1 and later,
    SATAN even attempts to protect you after the password has fallen
    into the hands of unauthorized users:

    * SATAN displays a warning and advises the user to not contact
      other HTML servers from within a SATAN session, when it finds
      that the HTML client program reveals SATAN password information
      as part of parent URL information.

    * SATAN rejects requests that appear to come from hosts other than
      the one it is running on, that refer to resources outside its own
      HTML tree, or that contain unexpected data.

    * SATAN terminates with a warning when it finds a valid SATAN
      password in an illegal request: SATAN assumes the password has
      fallen into the hands of unauthorized users and assumes the
      worst.

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The CERT Coordination Center staff thanks Wietse Venema for his cooperation
and assistance with this revised advisory.
- ------------------------------------------------------------------------------

If you believe that your system has been compromised, contact the CERT
Coordination Center or your representative in the Forum of Incident
Response and Security Teams (FIRST).

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

Internet E-mail: cert@cert.org
Telephone: +1 412-268-7090 (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.
Fax: +1 412-268-6989

Postal address:  CERT Coordination Center
                 Software Engineering Institute
                 Carnegie Mellon University
                 Pittsburgh, PA 15213-3890
                 USA

CERT advisories and bulletins are posted on the USENET newsgroup
comp.security.announce. If you would like to have future advisories and
bulletins mailed to you or to a mail exploder at your site, please send mail
to cert-advisory-request@cert.org.

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


Copyright 1995 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.

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

Aug. 30, 1996 - Information previously in the CA-95:07 and CA-95:07a README
                files was inserted into the advisory.



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