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CERT® Advisory CA-1992-03 Internet Intruder Activity

Original issue date: February 17,1992
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 regarding a significant intrusion incident on the Internet. Systems administrators should be aware that many systems on the Internet have been compromised due to this activity. To identify whether your systems have been affected by the activity we recommend that all system administrators check for the signs of intrusion detailed in this advisory.

This advisory describes the activities that have been identified as part of this particular incident. This does not address the possibility that systems may have been compromised due to other, unrelated intrusion activity.

I. Description

The intruders gained initial access to a host by discovering a password for a user account on the system. They then attempted to become root on the compromised system.

II. Impact

Having gained root access on a system, the intruders installed trojan binaries that captured account information for both local and remote systems. They also installed set-uid root shells to be used for easy root access.

III. Solution

A. Check your systems for signs of intrusion due to this incident.

  1. Check the su, ftpd, and ftp binaries (for example, "/bin/su", "/usr/ucb/ftp" and "/usr/etc/in.ftpd" on Sun systems) against copies from distribution media.

  2. Check for the presence of any of the following files:
    "/usr/etc/..." (dot dot dot), "/var/crash/..." (dot dot dot), "/usr/etc/.getwd", "/var/crash/.getwd", or "/usr/kvm/..." (dot dot dot).

  3. Check for the presence of "+" in the "/etc/hosts.equiv" file.

  4. Check the home directory for each entry in the "/etc/passwd" file for the presence of a ".rhosts" file containing "+ +" (plus space plus).

  5. Search the system for the presence of the following set-uid root files: "wtrunc" and ".a".

  6. Check for the presence of the set-uid root file "/usr/lib/lpx".

B. Take the following steps to secure your systems.

  1. Save copies of the identified files to removable media.

  2. Replace any modified binaries with copies from distribution media.

  3. Remove the "+" entry from the "/etc/hosts.equiv" file and the "+ +" (plus space plus) entry from any ".rhosts" files.

  4. Remove any of the set-uid root files that you find, which are mentioned in A5 or A6 above.

  5. Change every password on the system.

  6. Inspect the files mentioned in A2 above for references to other hosts.

This document is available from: http://www.cert.org/advisories/CA-1992-03.html

CERT/CC Contact Information

Email: cert@cert.org
Phone: +1 412-268-7090 (24-hour hotline)
Fax: +1 412-268-6989
Postal address:
CERT Coordination Center
Software Engineering Institute
Carnegie Mellon University
Pittsburgh PA 15213-3890
U.S.A.

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.

Using encryption

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 information.

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.

NO WARRANTY
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 infringement.

Conditions for use, disclaimers, and sponsorship information

Copyright 1992 Carnegie Mellon University.

Revision History 
September 19,1997  Attached Copyright Statement