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Security Bulletin 9207                  DISA Defense Communications System
February 26, 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-9207).
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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-92:04                        CERT Advisory
                             February 25, 1992
                      AT&T /usr/etc/rexecd Vulnerability

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 The Computer Emergency Response Team/Coordination Center (CERT/CC) has
 received information concerning a vulnerability in AT&T TCP/IP Release
 4.0 running on SVR4 systems for both the 386/486 and 3B2 RISC platforms.

 The existing error, in the remote execution server /usr/etc/rexecd, has
 been corrected, and a new executable for rexecd is available from AT&T
 by calling 800-543-9935.  Patches may be obtained outside the U.S. by
 calling your local technical support.  The numbers associated with the
 fix are 5127 (3.5" media) and 5128 (5.25" media).

 The problem does not exist in TCP/IP release 3.2 for SVR3, or any earlier
 versions of the TCP/IP product running on either the 3B2 or 386 platforms.

 The version of TCP/IP distributed with SVR4 by UNIX(r) System Laboratories,
 Inc. (a subsidiary of AT&T) does not contain this vulnerability.

 UNIX(r) is a registered trademark of UNIX System Laboratories, Inc.

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 I.   Description

      A vulnerability has been identified where root privileges may be
      accessed through the use of /usr/etc/rexecd.

 II.  Impact

      A user on a remote machine may be able to run commands as root on
      the target host (the host running the affected /usr/etc/rexecd).

 III. Solution

      1. Administrators of affected systems should execute, as root, the
         following command to immediately turn off access to rexecd until
         the new binary can be obtained.

         # chmod 400 /usr/etc/rexecd

      2. Obtain and install the new patch.  The fix will be supplied as
         one diskette, and it comes with one page of instructions documenting
         the procedure to replace the existing /usr/etc/rexecd binary.

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 The CERT/CC wishes to thank Bradley E. Smith, Network & Technical Services,
 Bradley University, for bringing this vulnerability to our attention and for
 providing a corresponding solution.  We would also like to thank AT&T for
 their very 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.sei.cmu.edu (192.88.209.5).


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 The point of contact for MILNET security-related incidents is the
 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 on federal holidays.

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