AT&T /usr/etc/rexecd Vulnerability
Original issue date: February 25, 1992
Last revised: September 19, 1997
Attached copyright statement
A complete revision history is at the end of this file.
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.
A vulnerability has been identified where root privileges may be
accessed through the use of /usr/etc/rexecd.
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).
- 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
- 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.
This document is available from:
CERT/CC Contact Information
Phone: +1 412-268-7090 (24-hour hotline)
Fax: +1 412-268-6989
CERT Coordination Center
Software Engineering Institute
Carnegie Mellon University
Pittsburgh PA 15213-3890
CERT/CC personnel answer the hotline 08:00-17:00 EST(GMT-5) / EDT(GMT-4)
Monday through Friday; they are on call for emergencies during other
hours, on U.S. holidays, and on weekends.
We strongly urge you to encrypt sensitive information sent by
email. Our public PGP key is available from
If you prefer to use DES, please call the CERT hotline for more
Getting security information
CERT publications and other security information are available from
our web site
* "CERT" and "CERT Coordination Center" are registered in the U.S. Patent and Trademark Office.
Any material furnished by Carnegie Mellon University and the
Software Engineering Institute is furnished on an "as is"
basis. Carnegie Mellon University makes no warranties of any kind,
either expressed or implied as to any matter including, but not
limited to, warranty of fitness for a particular purpose or
merchantability, exclusivity or results obtained from use of the
material. Carnegie Mellon University does not make any warranty of any
kind with respect to freedom from patent, trademark, or copyright
Conditions for use, disclaimers, and sponsorship information
Copyright 1992 Carnegie Mellon University.
September 19,1997 Attached Copyright Statement