CERT Advisory - AT&T /usr/etc/rexecd Vulnerability

CERT Advisory cert-advisory-request at cert.sei.cmu.edu
Tue Feb 25 17:42:30 UTC 1992

CA-92:04                        CERT Advisory
                              February 25, 1992
                       AT&T /usr/etc/rexecd Vulnerability 


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.


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.

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.

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 at cert.sei.cmu.edu
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 (

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