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Home : Advisories : Altered System Binaries Incident

Title: Altered System Binaries Incident
Released by: CERT
Date: 22nd June 1992
Printable version: Click here

Hash: SHA1



Last Revised: September 19,1997

                                  CERT Advisory

                                June 22, 1992

                       Altered System Binaries Incident

- ---------------------------------------------------------------------------

The Computer Emergency Response Team/Coordination Center (CERT/CC) has

received information regarding a series of significant intrusion

incidents 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 gain initial access to a host by discovering a

     password for a user account on the system, exploiting a "+" in 

     the "/etc/hosts.equiv" file, or any ".rhosts" files on the

     system.  The intruder then connects to the system using rsh and

     attempts to become root on the compromised system.  An alias of

     "decode" may used to gain root privileges.

II.  Impact


     Having gained root access on a system, the intruders may make

     unauthorized changes to system binaries that can capture account

     information for both local and remote systems.  In addition, the

     intruder adds "+ +" to any ".rhosts" files to which the intruder

     has access.

III. Solution 

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

        1. Check the login, telnet, and uucpd binaries (for example,

           "/bin/login", "/usr/ucb/telnet", and "/usr/etc/in.uucpd" on

           Sun systems) against copies from distribution media.  Note that

           a check for creation or modification times and sizes is

           not sufficient to assure that the files have not been modified.

           The CERT/CC suggests that you compare the output of the

           "sum(1)" or "cmp(1)" command on both the distribution and

           installed versions of the binaries.

        2. If the check from (A.1) indicates that your binaries have been

           modified, check for the presence of a password

           log file.  Since the name of the logfile is often changed,

           the name of the file should be obtained using the

           "strings(1)" command on the Trojan login, uucpd, or telnet

           binary.  Examples of filenames used on other systems are:

                               "/usr/spool/. " (dot space)











           Verify that the contents of files found using the "strings(1)"

           command do not contain valid username/password combinations.  

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


           NOTE that Sun Microsystems installs the SunOS

           operating system with a default "+" in the /etc/hosts.equiv

           file for easy network access.  This should be removed

           unless required in your operating environment and protected

           by a firewall network configuration.  Leaving the "+"

           intact will allow any non-root user on the Internet to

           login to the system without a password.

        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. Assure that your "/etc/fstab", "/etc/inetd.conf", and

           "/etc/exports" files have not been modified.

     B. Take the following steps to secure your systems.

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

           remove any password log files as found in (A.2) above.

        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. Change ownership of the "/etc" directory to userid "root"

           if it is owned by "bin" (as distributed by Sun).


        5. Change every password on the system and assure that the new 

           passwords are robust using a package such as Crack or Cops

           (available via anonymous ftp from cert.org).

        6. Inspect and restore any changes made to your "/etc/fstab", 

           "/etc/exports", or "/etc/inetd.conf" files.  If any

           modifications are found in these files, you will need to

           unmount file systems and restart daemons once the files

           have been restored.  Alternatively the system could be



        7. Remove the "decode" alias from your global mail aliases

           file ("/etc/aliases" on Sun systems, "/usr/lib/aliases" on

           other UNIX systems).

- ---------------------------------------------------------------------------

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@cert.org

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.org (

- ------------------------------------------------------------------------------

Copyright 1992 Carnegie Mellon University. Conditions for use, disclaimers,

and sponsorship information can be found in

http://www.cert.org/legal_stuff.html and http://ftp.cert.org/pub/legal_stuff .

If you do not have FTP or web access, send mail to cert@cert.org with

"copyright" in the subject line.

CERT is registered in the U.S. Patent and Trademark Office.


Revision History:

September 19,1997  Attached Copyright Statement


Version: PGP for Personal Privacy 5.0

Charset: noconv





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