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Security Bulletin 9214                  DISA Defense Communications System
May 27, 1992                Published by: DDN Security Coordination Center
                                     ([email protected])   1-(800) 365-3642

                       DEFENSE  DATA  NETWORK
                         SECURITY  BULLETIN

 The DDN SECURITY BULLETIN is distributed by the DDN SCC (Security
 Coordination Center) under DISA contract as a means of communicating
 information on network and host security exposures, fixes, and concerns
 to security and management personnel at DDN facilities.  Back issues may
 be obtained via FTP (or Kermit) from NIC.DDN.MIL [192.112.36.5]
 using login="anonymous" and password="guest".  The bulletin pathname is
 scc/ddn-security-yynn (where "yy" is the year the bulletin is issued
 and "nn" is a bulletin number, e.g. scc/ddn-security-9214).
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!                                                                       !
!     The following important  advisory was  issued by the Computer     !
!     Emergency Response Team (CERT)  and is being relayed unedited     !
!     via the Defense Information Systems Agency's Security             !
!     Coordination Center  distribution  system  as a  means  of        !
!     providing  DDN subscribers with useful security information.      !
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===========================================================================
CA-92:10                        CERT Advisory
                               May 26, 1992
                         AIX crontab Vulnerability

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

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 modules older 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.  Outside the U.S., patches
            may be obtainedby 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

            You must use binary mode to retrieve the patch.

    - 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: [email protected]
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).

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