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  • CERT Advisory CA-1992-05 AIX REXD Daemon Vulnerability

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Original issue date: March 5, 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 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.

Copyright 1992 Carnegie Mellon University.

Revision History
September 19,1997  Attached copyright statement
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