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Home : Advisories : AIX crontab Vulnerability

Title: AIX crontab Vulnerability
Released by: CERT
Date: 26th May 1992
Printable version: Click here

Hash: SHA1



Last Revised: September 19,1997

                Attached copyright statement  

                              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 older modules than the above output indicates, we

suggest that you install the fix.

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

I.   Description

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



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


           2. If you are on the Internet, use anonymous ftp to obtain

              the fix from software.watson.ibm.com (

              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.

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

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.

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

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 (

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

Copyright 1992 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.


Revision History:

September 19,1997  Attached Copyright Statement


Version: PGP for Personal Privacy 5.0

Charset: noconv





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