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Security Advisory                                                       CERT-NL
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Author/Source : CERT-NL (Erik-Jan Bos)                      Index  :    S-93-08
Distribution  : SURFnet Constituency                        Page   :          1
Classification: External                                    Version:      Final
Subject       : Commodore Amiga UNIX finger Vulnerability   Date   :  19-Feb-93
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CERT-NL has received information concerning a vulnerability in the
"finger" program of Commodore Business Machine's Amiga UNIX product.
The vulnerability affects Commodore Amiga UNIX versions 1.1, 2.03, 2.1,
2.1p1, 2.1p2, and 2.1p2a. Commodore is aware of the vulnerability, and
both a workaround and a patch are available. Affected sites should
apply either the workaround or the patch, and directions are provided
below.

If you have any further questions, contact Commodore's David Miller
via e-mail. David's e-mail address is davidm@commodore.com.

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I.    Description

      The "finger" command in Amiga UNIX contains a security
      vulnerability.


II.   Impact

      Non-privileged users can gain unauthorized access to files.


III.  Solution

      Commodore has suggested a workaround and a patch, as follows:

      A. Workaround

         As root, modify the permission of the existing /usr/bin/finger
         to prevent misuse.

                # /bin/chmod 0755 /usr/bin/finger

      B. Patch

         As root, install the "pubsrc" package from the distribution tape. 

         In the file, "/usr/src/pub/cmd/finger/src/finger.c", add the line:

                setuid(getuid());

         immediately before the line reading:

                display_finger(finger_list);

         (Optionally) save a copy of the existing /usr/bin/finger and modify
         its permission to prevent misuse.

                # /bin/mv /usr/bin/finger /usr/bin/finger.orig
                # /bin/chmod 0755 /usr/bin/finger.orig

         In the directory, "/usr/src/pub/cmd/finger", issue the command:

                # cd /usr/src/pub/cmd/finger
                # make install


NOTE: Although the file mode "755" ensures that the vulnerability can not
be exploited, CERT-NL advises to use "700" instead, in order to make the
"vulnerable" file unreadable for further use.


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CERT-NL wishes to thank CERT Coordination Center for bringing this
information to our attention. CERT-NL also wishes to thank Commodore
Business Machines for their response to this case.

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CERT-NL is the Computer Emergency Response Team, located in The
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and Security Teams (FIRST). The constituency of CERT-NL are the SURFnet
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In case of computer or network security problems please contact CERT-NL
or the CERT of your own constituency. Please be aware of the fact that
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Email:     cert-nl@surfnet.nl
Phone:     +31 30 310290
Fax:       +31 30 340903
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           Attn. CERT-NL
           P.O. Box 19035
           NL - 3501 DA  UTRECHT
           The Netherlands
A 7*24h phonenumber is available to SURFnet SSC's and FIRST members on request
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