Archive of CERT general posting, CERT Advisory CA-97.18 - Vulnerability in the at(1) program

12/06/97, CERT Advisory CA-97.18 - Vulnerability in the at(1) program
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To: cert-advisory@cert.org
Subject: CERT Advisory CA-97.18 - Vulnerability in the at(1) program
From: CERT Advisory <cert-advisory@cert.org>
Date: Thu, 12 Jun 1997 10:24:08 -0400
Organization: CERT(sm) Coordination Center - +1 412-268-7090
Reply-To: cert-advisory-request@cert.org

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=============================================================================
CERT* Advisory CA-97.18
Original issue date: June 12, 1997
Last revised: --

Topic: Vulnerability in the at(1) program
- -----------------------------------------------------------------------------
The CERT Coordination Center has received reports of a buffer overflow
condition in some versions of the at(1) program. By carefully specifying the
data that overflows this buffer, any user can execute arbitrary commands as
root.

The CERT/CC team recommends installing a vendor patch if one is available
(see Section III.A). Until you can do so, we recommend disabling at(1) (see
Section III.B).

We will update this advisory as we receive additional information. Please
check advisory files regularly for updates that relate to your site.

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

I.   Description

     The at(1) program can be used by local users to schedule commands to be
     executed at a later time. When those commands are run, they are run as
     the user who originally ran at(1). That user will be referred to as the
     scheduling user.

     As a precaution, the scheduling user's list of commands is stored in a
     file in a directory that is not writable by other users. The file's
     ownership is changed to that of the scheduling user, and that
     information is used to define the identity of the process that runs the
     commands when the appointed time arrives. These measures are intended
     to prevent other users from changing the scheduling user's list of
     commands or creating new lists to be executed as another user. To
     achieve this additional level of security, the at(1) program runs as
     set-user-id root.

     Some versions of at(1) contain a programming defect that can result in a
     buffer local to at(1) being overflowed. Through the careful specification
     of the data that overflows this buffer, arbitrary commands can be executed
     with the identity of at(1) process, root in this case.

II.  Impact

     Any user with an account on a system that contains a defective version
     of at(1) can execute programs as root.

III. Solution

     A.  Install a patch from your vendor

         Below is a list of vendors who have provided information about
         at. Details are in Appendix A of this advisory; we will update
         the appendix as we receive more information. If your vendor's
         name is not on this list, the CERT/CC did not hear from that
         vendor. Please contact your vendor directly.

         Cray Research - A Silicon Graphics Company
         Hewlett-Packard Company
         IBM Corporation
         Santa Cruz Operation, Inc. (SCO)
         Silicon Graphics, Inc.
         Sun Microsystems, Inc.


     B.  Until you are able to install the appropriate patch, we recommend
         the following workaround:

         Turn off at(1) by setting its mode to 0. Do the following as
         root:

                # chmod 0 /usr/bin/at

         Note that the location of at(1) varies from system to system.
         Consult your system's documentation for the correct location.

         After you turn off the at(1) command, users will not be able to use
         it.  As an alternative to at(1), consider using the crontab(1)
         command if your system provides it.


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

Appendix A - Vendor Information

Below is a list of the vendors who have provided information for this
advisory. We will update this appendix as we receive additional information.
If you do not see your vendor's name, the CERT/CC did not hear from that
vendor. Please contact the vendor directly.

Cray Research - A Silicon Graphics Company
==========================================
  Neither Unicos nor Unicos/mk is believed to be vulnerable.

Hewlett-Packard Company
=======================
  Hewlett Packard is currently investigating the problem. We will update this
  advisory through the CERT/CC when the investigation is complete.

IBM Corporation
===============
  See the appropriate release below to determine your action.


  AIX 3.2
  -------
    Apply the following fixes to your system:

       PTF - U443452 U443486 U444191 U444206 U444213 U444243
       APAR - IX60796

    To determine if you have these PTFs on your system, run the following
    commands:

       lslpp -lB U443452 U443486 U444191 U444206 U444213 U444243


  AIX 4.1
  -------
    Apply the following fixes to your system:

        APAR - IX60894
        APAR - IX60890

    To determine if you have this APAR on your system, run the following
    commands:

       instfix -ik IX60894
       instfix -ik IX60890

    Or run the following commands:

       lslpp -h bos.rte.cron
       lslpp -h bos.rte.libc

    Your version of bos.rte.cron should be 4.1.4.8 or later.
    Your version of bos.rte.libc should be 4.1.4.18 or later.


  AIX 4.2
  -------
    Apply the following fixes to your system:

        APAR - IX60892
        APAR - IX61125

    To determine if you have this APAR on your system, run the following
    commands:

       instfix -ik IX60892
       instfix -ik IX61125

    Or run the following commands:

       lslpp -h bos.rte.cron
       lslpp -h bos.rte.libc

    Your version of bos.rte.cron should be 4.2.0.1 or later.
    Your version of bos.rte.libc should be 4.2.0.5 or later.


  To Order
  --------
    APARs may be ordered using Electronic Fix Distribution (via FixDist)
    or from the IBM Support Center. For more information on FixDist,
    reference URL:

       http://service.software.ibm.com/aixsupport/

    or send e-mail to aixserv@austin.ibm.com with a subject of "FixDist".


  IBM and AIX are registered trademarks of International Business Machines
  Corporation.


Santa Cruz Operation, Inc. (SCO)
================================
  All SCO operating systems are vulnerable. SCO has made an interim fix
  available for anonymous ftp:

        ftp://ftp.sco.com/SSE/sse007.ltr.Z - cover letter
        ftp://ftp.sco.com/SSE/sse007.tar.Z - replacement binaries

  The fix includes binaries for the following SCO operating systems:

        - SCO CMW+ 3.0
        - SCO Open Desktop/Open Server 3.0, SCO UNIX 3.2v4
        - SCO OpenServer 5.0
        - SCO UnixWare 2.1


Silicon Graphics, Inc.
======================
  At this time, Silicon Graphics does not have any public information
  for the at(1) issue.  Silicon Graphics has communicated with CERT
  and other external security parties and is actively investigating
  this issue.   When more Silicon Graphics information (including any
  possible patches) is available for release, that information will
  be released via the SGI security mailing list, wiretap.

  For subscribing to the wiretap mailing list and other SGI security
  related information, please refer to the Silicon Graphics Security
  Headquarters website located at:

          http://www.sgi.com/Support/Secur/security.html


Sun Microsystems, Inc.
======================
  Sun will be producing patches.


- -----------------------------------------------------------------------------
Technical information for this advisory was drawn in part from a posting by
Don Farmer to the bugtraq mailing list. Thanks to Wolfgang Ley of DFN-CERT for
his help in developing this advisory.
- -----------------------------------------------------------------------------

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 (see http://www.first.org/team-info).


CERT/CC Contact Information
- ----------------------------
Email    cert@cert.org

Phone    +1 412-268-7090 (24-hour hotline)
                CERT personnel answer 8:30-5:00 p.m. EST(GMT-5) / EDT(GMT-4)
                and are on call for emergencies during other hours.

Fax      +1 412-268-6989

Postal address
         CERT Coordination Center
         Software Engineering Institute
         Carnegie Mellon University
         Pittsburgh PA 15213-3890
         USA

Using encryption
   We strongly urge you to encrypt sensitive information sent by email. We can
   support a shared DES key or PGP. Contact the CERT/CC for more information.
   Location of CERT PGP key
         ftp://info.cert.org/pub/CERT_PGP.key

Getting security information
   CERT publications and other security information are available from
        http://www.cert.org/
        ftp://info.cert.org/pub/

   CERT advisories and bulletins are also posted on the USENET newsgroup
        comp.security.announce

   To be added to our mailing list for advisories and bulletins, send
   email to
        cert-advisory-request@cert.org
   In the subject line, type
        SUBSCRIBE  your-email-address

- ---------------------------------------------------------------------------
Copyright 1997 Carnegie Mellon University
This material may be reproduced and distributed without permission provided
it is used for non-commercial purposes and the copyright statement is
included.

* Registered U.S. Patent and Trademark Office.
- ---------------------------------------------------------------------------

This file: ftp://info.cert.org/pub/cert_advisories/CA-97.18.at
           http://www.cert.org
               click on "CERT Advisories"


~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Revision history

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