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CERT Advisory CA-96.18 - Vulnerability in fm_fls
From: cert-advisory () cert org (CERT Advisory)
Date: Wed, 14 Aug 1996 13:21:20 -0500


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=============================================================================
CERT(sm) Advisory CA-96.18
August 14, 1996

Topic: Vulnerability in fm_fls
- -----------------------------------------------------------------------------

The CERT Coordination Center has received reports of a configuration problem
in the floating license server for Adobe FrameMaker (fm_fls) that enables
non-privileged users to make any file world-readable and world-writable.
Exploitation scripts are publicly available.

Any system that includes a setuid version of fm_fls is vulnerable.
Adobe Systems reports that the following Adobe products use fm_fls:

    Frame Products, version 4
          FrameMaker
          FrameViewer
          FrameBuilder

    Frame Products, version 5
          FrameMaker
          FrameMaker+SGML

The CERT/CC team recommends installing a patch from your vendor. Until you
can obtain a patch, we urge you to remove the setuid bit from all instances
of fm_fls.

As we receive additional information relating to this advisory, we will
place it in
        ftp://info.cert.org/pub/cert_advisories/CA-96.18.README

We encourage you to check our README files regularly for updates on
advisories that relate to your site.

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

I.   Description

     FrameMaker is a commercial text-processing software package
     available from Adobe Systems, Inc. It is also available from other
     vendors as part of their product line offering.

     When FrameMaker versions 4.X or 5.X are installed, the installation
     script provided with FrameMaker installs a file named fm_fls that is
     setuid to installing user, typically the root user. fm_fls is typically
     found in the FrameMaker installation tree. Consult your documentation
     for precise location of fm_fls.

     When fm_fls runs, it opens up a log file, which by default is
     /tmp/fm_fls.log. In normal operation, fm_fls writes logging information
     about license usage to the named log file. However, when given invalid
     arguments, fm_fls writes these arguments to the log file, changes the
     owner of the log file to root or whoever installed fm_fls, changes the
     permissions to world-readable and world-writable, and then exits.
     Therefore, by giving fm_fls invalid arguments and naming another file as
     the log file, a user can make that file world-readable and world-writable.

     Adobe Systems reports that fm_fls is installed as setuid root because
     it registers the license manager program with the the program number
     mapper, also known as portmap or rpcbind. On some platforms, only the
     original user (in this case root) or the root user has permission to
     remove a registration. fm_fls will attempt to remove a previous
     registration when it is restarted. With fm_fls setuid root, restarting
     fm_fls ensures that all changes made in the program number mapper are
     successful because they are done by the same user.

     The floating license servers shipped with and installed by FrameMaker
     4.X and 5.X are vulnerable. Similarly, any other system that includes
     a setuid version of fm_fls is vulnerable. Exploitation scripts are
     publicly available.

II.  Impact

     Anyone with access to an account on an unpatched system can create
     world-writable and world-readable files; it is then easy to gain root
     access.

III. Solution

      Obtain and install a vendor patch when it becomes available.

      In the meantime, remove the setuid bit from all instances of fm_fls.
      To determine if a system is vulnerable and to disable the programs that
      are believed to be vulnerable, use the find command we provide below or
      a variant. Consult your local system documentation to determine how to
      tailor the find program on your system.

      You will need to run the find command on each system you maintain
      because the command examines files on the local disk only. Substitute
      the names of your local file systems for FILE_SYSTEM_NAMES in the
      example. Example local file system names are /, /usr, and /var.

      To find all instances of fm_fls and then to remove the setuid bit from
      them, do the following as root. Note that this is one long command,
      though we have separated it onto two lines using a back-slash.

             find FILE_SYSTEM_NAMES -xdev -type f -name fm_fls -perm -04000 \
                 -print -ok chmod u-s '{}' \;

        This command will find all files on a system that are
            - only in the file system you name (FILE_SYSTEM_NAMES -xdev)
            - regular files (-type f)
            - named fm_fls
            - setuid (-perm -04000)

        Once found, those files will
            - have their names printed (-print)
            - have the setuid mode removed, but only if you type `y'
              in response to the prompt (-ok chmod u-s '{}' \;)

      With the setuid root bit removed, fm_fls must then be started each
      time by the same user. That user should be root so that the previous
      registration can be successfully removed no matter what platform
      fm_fls is running on.

      In addition, the log file, license.log, should be stored in a non-public
      directory; specify this new location with the -log command line argument.
      Consult the documentation that comes with FrameMaker versions 4.X and
      5.X to learn how to do this on your system.

- ---------------------------------------------------------------------------
The CERT Coordination Center staff thanks Adobe Systems for their support
in the development of this 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).

We strongly urge you to encrypt any sensitive information you send by email.
The CERT Coordination Center can support a shared DES key and PGP. Contact
the CERT staff for more information.

Location of CERT PGP key
         ftp://info.cert.org/pub/CERT_PGP.key

CERT Contact Information
- ------------------------
Email    cert () cert org

Phone    +1 412-268-7090 (24-hour hotline)
                CERT personnel answer 8:30-5:00 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 publications, information about FIRST representatives, and other
security-related information are available for anonymous FTP from
        http://www.cert.org/
        ftp://info.cert.org/pub/

CERT advisories and bulletins are also posted on the USENET newsgroup
        comp.security.announce

To be added to our mailing list for CERT advisories and bulletins, send your
email address to
        cert-advisory-request () cert org


Copyright 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.

This file: ftp://info.cert.org/pub/cert_advisories/CA-96.18.fm_fls
           http://www.cert.org
               click on "CERT Advisories"

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