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Security Bulletin 9208                  DISA Defense Communications System
9 March 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-9208).
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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-92:05                        CERT Advisory
                               March 5, 1992
                       AIX REXD Daemon Vulnerability

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The Computer Emergency Response Team/Coordination Center (CERT/CC) has
received information concerning a vulnerability with the rexd daemon
in versions 3.1 and 3.2 of AIX for IBM RS/6000 machines.

IBM is aware of the problem and it will be fixed in future updates to
AIX 3.1 and 3.2.  Sites may call IBM Support (800-237-5511) and ask for
the patch for apar ix21353.  Patches may be obtained outside the U.S. by
contacting your local IBM representative.

The fix is also provided below.

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I.   Description

    In certain configurations, particularly if NFS is installed,
    the rexd (RPC remote program execution) daemon is enabled.

    Note: Installing NFS with the current versions of "mknfs" will
    re-enable rexd even if it was previously disabled.

II.  Impact

    If a system allows rexd connections, anyone on the Internet can
    gain access to the system as a user other than root.

III. Solution

    CERT/CC and IBM recommend that sites take the following actions
    immediately.  These steps should also be taken whenever "mknfs" is run.

    1.  Be sure the rexd line in /etc/inetd.conf is commented out by
        placing a '#' at the beginning of the line:

        #rexd   sunrpc_tcp tcp  wait  root  /usr/etc/rpc.rexd rexd 100017 1

    2.  Refresh inetd by running the following command as root:

        refresh -s inetd


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The CERT/CC wishes to thank Darren Reed of the Australian National
University for bringing this vulnerability to our attention and
IBM for their response to the 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.sei.cmu.edu (192.88.209.5).

Posted-Date:  Thu, 5 Mar 92 14:05:19 EST
Received-Date:  Thu, 5 Mar 92 14:03:06 EST
Return-Path:  <[email protected]>


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The point of contact for MILNET security-related incidents is the
DDN Security Coordination Center (SCC).

E-mail address: [email protected]

Telephone: 1-(800)-365-3642
     NIC Help Desk personnel are available from 7:00 a.m.-7:00 p.m. EST,
     Monday through Friday except federal holidays.

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