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CA-92:10                        CERT Advisory
                                May 26, 1992
                          AIX crontab Vulnerability

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The Computer Emergency Response Team/Coordination Center (CERT/CC) has
received information concerning a vulnerability in crontab(1) in version 3.2
of IBM's AIX operating system.

IBM is aware of this problem and a fix is available as apar number "ix26997"
for AIX version 3.2.  The version information for the patched /usr/bin/crontab
is shown in the following what(1) output:

% what /usr/bin/crontab
04 1.23 com/cmd/cntl/cron/crontab.c, cmdcntl, bos320, 9218320f 4/8/92 11:50:42
07 1.8  com/cmd/cntl/cron/permit.c, bos, bos320 4/25/91 17:16:59
11 1.15  com/cmd/cntl/cron/cronsub.c, bos, bos320 8/18/91 20:42:32
06 1.9  com/cmd/cntl/cron/funcs.c, bos, bos320 6/8/91 21:22:40

If your crontab contains older modules than the above output indicates, we
suggest that you install the fix.

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I.   Description

     The distributed version of /usr/bin/crontab contains a security
     vulnerability.
     

II.  Impact

     Local users can gain unauthorized root access to the system.


III. Solution

      The CERT/CC suggests that sites install the fix that IBM has made
      available.  As an interim step, we suggests that sites prevent all
      non-root users from running /usr/bin/crontab by removing (or renaming)
      the /var/adm/cron/cron.allow and /var/adm/cron/cron.deny files.

      - Obtain the fix from IBM Support.

           1. To order from IBM call 1-800-237-5511 and ask
              that the fix be shipped.  Patches may be obtained
              outside the U.S. by contacting your local IBM
              representative.

           2. If you are on the Internet, use anonymous ftp to obtain
              the fix from software.watson.ibm.com (129.34.139.5).

              Patch           Filename                Checksum
              AIX 3.2         pub/aix3/cronta.tar.Z   02324   154

              The patch must be retrieved using binary mode.

      - Install the fix following the instructions in the README file.

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The CERT/CC would like to thank Fuat Baran of Advanced Network & Services,
Inc. for bringing this security vulnerability to our attention and IBM for
their quick response to this problem.
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If you believe that your system has been compromised, contact CERT/CC or
your representative in FIRST (Forum of Incident Response and Security Teams).

Internet E-mail: cert@cert.org
Telephone: 412-268-7090 (24-hour hotline)
           CERT/CC personnel answer 7:30 a.m.-6:00 p.m. EST(GMT-5)/EDT(GMT-4),
           on call for emergencies during other hours.

Computer Emergency Response Team/Coordination Center (CERT/CC)
Software Engineering Institute
Carnegie Mellon University
Pittsburgh, PA 15213-3890

Past advisories, information about FIRST representatives, and other
information related to computer security are available for anonymous ftp
from cert.org (192.88.209.5).