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CERT(*) Advisory CA-95:07a

Original issue date:  April 21, 1995

Last revised: September 23, 1997

                Update copyrigth statement



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



             http://ftp.win.tue.nl/pub/security/satan-1.1.1.tar.Z

             http://ftp.win.tue.nl/pub/security/satan-1.1.1.README

             http://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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ZCkBoyvBcmXEi+J7eDBbWLPDxeDimgrORbAIQ4uikRafs8KlpNyA8qbVMny5AAUR

tCV3aWV0c2UgdmVuZW1hIDx3aWV0c2VAd3p2Lndpbi50dWUubmw+

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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.

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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.



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Copyright 1995 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.





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Revision history



Sep. 23, 1997  Update copyright statement

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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