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CERT(*) Advisory CA-96.18

Original issue date: August 14, 1996

Last Revised: September 24, 1997

              Updated copyright statement



              A complete revision history is at the end of this file.





Topic: Vulnerability in fm_fls

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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.



We will update this advisory as we receive additional information.

Please check advisory files regularly for updates that relate to your site.

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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; this can lead to gaining

     root access.



III. Solution



     A. 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.



     B. Another possible solution is to create a new userid and group, say UID

        frame and GID frame, with no one in group frame except for UID frame,

        and make fm_fls mode 4110.  For example, on Solaris 2.4, 2.5, or 2.5.1:



- - ---s--x---   1 frame    frame     145736 Aug 24  1995 /usr/local/frame5.0/bin/sunxm.s5.sparc/fm_fls



        In this case the log file has to be created manually just once by root

        (if you keep it permanently in /var/log instead of /tmp) and

        chown'd/chgrp'd to frame/frame with mode 644 (though fm_fls resets

        that to 666).



        At boot time root runs the frame5.0/bin/fm_fls wrapper which ends up

        invoking the setuid-frame fm_fls binary.  That could be done instead

        using 'su - frame -c frame_startup_command...' as an extra precaution

        if UID frame has a real shell.  In that case you might as well remove

        the setuid bit too.



        This has been working for about a year.



..............................................................................

Appendix A



The following is vendor-supplied information.

For the most up-to-date information, contact your vendor.



BSDI

        Does not ship Frame with BSD/OS.



Digital Equipment Corporation

        Does not distribute this product with it's operating

        systems.



Open Software Foundation (OSF)

        Does not support the software with this problem.



Sun Microsystems, Inc.

        Does not ship FrameMaker.





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The CERT Coordination Center staff thanks Adobe Systems for their support

in the development of this 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).



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

         http://info.cert.org/pub/CERT_PGP.key



CERT Contact Information

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

Email    cert@cert.org



Phone    +1 412-268-7090 (24-hour hotline)

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Postal address

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        Software Engineering Institute

        Carnegie Mellon University

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        USA



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Copyright 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.





 This file: http://info.cert.org/pub/cert_advisories/CA-96.18.fm_fls

            http://www.cert.org

                click on "CERT Advisories"





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 Revision history



 Sep. 24, 1997  Updated copyright statement

Aug. 30, 1996  Information previously in the README was inserted into the

               advisory.

Aug. 21, 1996  Added Section III.B (provides another possible solution).

Aug. 15, 1996  Added Appendix A - vendor information.







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