CERT Advisory - AIX REXD Daemon Vulnerability

CERT Advisory cert-advisory-request at cert.sei.cmu.edu
Thu Mar 5 19:07:10 UTC 1992

CA-92:05                        CERT Advisory
                                March 5, 1992
                        AIX REXD Daemon Vulnerability


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.


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
     having 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

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.

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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