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                   Date:         Thu, 6 Aug 1998 11:04:26 -0400
                   From:         X-Force <xforce@ISS.NET>
                   Subject:      ISS Security Advisory: cDc BackOrifice Backdoor

                   ISS Security Alert Advisory
                   August 6th, 1998


                   Cult of the Dead Cow Back Orifice Backdoor

                   Synopsis:

                   A hacker group known as the Cult of the Dead Cow has released a Windows
                   95/98 backdoor named 'Back Orifice' (BO).  Once installed this backdoor
                   allows unauthorized users to execute privileged operations on the affected
                   machine.

                   Back Orifice leaves evidence of its existence and can be detected and
                   removed.  The communications protocol and encryption used by this backdoor
                   has been broken by ISS X-Force.

                   Description:
                   A backdoor is a program that is designed to hide itself inside a target
                   host in order to allow the installing user access to the system at a later
                   time without using normal authorization or vulnerability exploitation.

                   Functionality:
                   The BO program is a backdoor designed for Windows 95/98. Once installed it
                   allows anyone who knows the listening port number and BO password to
                   remotely control the host.  Intruders access the BO server using either a
                   text or graphics based client.  The server allows intruders to execute
                   commands, list files, start silent services, share directories, upload and
                   download files, manipulate the registry, kill processes, list processes, as
                   well as other options.

                   Encrypted Communications:
                   All communications between backdoor client and the server use the User
                   Datagram Protocol (UDP).  All data sent between the client and server is
                   encrypted, however it is trivial to decrypt the data sent. X-Force has been
                   able to decrypt BO client requests without knowing the password and use the
                   gathered data to generate a password that will work on the BO server.

                   The way that BO encrypts its packets is to generate a 2 byte hash from the
                   password, and use the hash as the encryption key. The first 8 bytes of all
                   client request packets use the same string: "*!*QWTY?", thus it is very
                   easy to brute force the entire 64k key space of the password hash and
                   compare the result to the expected string. Once you know the correct hash
                   value that will decrypt packets, it is possible to start generating and
                   hashing random passwords to find a password that will work on the BO
                   server. In our tests in the X-Force lab, this entire process takes only a
                   few seconds, at most, on a Pentium-133 machine. With our tools we have been
                   able to capture a BO request packet, find a password that will work on the
                   BO server, and get the BO server to send a dialog message to warn the
                   administrator and kill its own process.

                   Determining if BO has been installed on your machine:
                   The BO server will do several things as it installs itself on a target
                   host:

                   * Install a copy of the BO server in the system directory
                   (c:\windows\system) either as " .exe" or a user specified file name.

                   * Create a registry key under
                   HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\RunServices
                   with the file name of the server file name and a description field of
                   either "(Default)" or a user specified description.

                   * The server will begin listening on UDP port 31337, or a UDP port
                   specified by the installer.  You can configure RealSecure to monitor for
                   network traffic on the default UDP 31337 port for possible warning signs.
                   In order to determine if you are vulnerable:
                   1. Start the regedit program (c:\windows\regedit.exe).
                   2. Access the key
                   HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\RunServices.
                   Look for any services that may not have been intentionally installed on the
                   machine.  If the length of one of these file is close to 124,928 (give or
                   take 30 bytes) then it is probably BO.

                   Recommended action:
                   BO can be removed by deleting the server and removing its registry entry.
                    If possible, you should back up all user data, format your hard drive, and
                   reinstall all operating systems and software on the infected machine.
                   However, if someone has installed BO on your machine, then it is most likely
                   part of a larger security breach.  You should react according to your site
                   security policy.


                   Determining the password and configuration of an installed BO:
                   1. Using a text editor like notepad, view the server exe file.
                   2. If the last line of the file is '8 8$8(8,8084888<8@8D8H8L8P8T8X8\8'8d8h8l8',
                   then the server is using the default configuration.  Otherwise, the
                   configuration will be the last several lines of this file, in this order:

                   <filename>
                   <service description>
                   <port number>
                   <password>
                   <optional plugin information>

                   Conclusion:
                   Back Orifice provides an easy method for intruders to install a backdoor on
                   a compromised machine.  Back Orifice's authentication and encryption is
                   weak, therefore an administrator can determine what activities and
                   information is being sent via BO.  Back Orifice can be detected and
                   removed.  This backdoor only works on Windows 95 and Windows 98 for now
                   and not currently on Windows NT.

                   ----------

                   Copyright (c) 1998 by Internet Security Systems, Inc.

                   Permission is hereby granted for the redistribution of this alert
                   electronically.  It is not to be edited in any way without express consent
                   of X-Force.  If you wish to reprint the whole or any part of this alert in
                   any other medium excluding electronic medium, please e-mail xforce@iss.net
                   for permission.

                   Disclaimer
                   The information within this paper may change without notice. Use of this
                   information constitutes acceptance for use in an AS IS condition. There are
                   NO warranties with regard to this information. In no event shall the author
                   be liable for any damages whatsoever arising out of or in connection with
                   the use or spread of this information. Any use of this information is at
                   the user's own risk.

                   X-Force PGP Key available at:   http://www.iss.net/xforce/sensitive.html as
                   well as on MIT's PGP key server and PGP.com's key server.

                   X-Force Vulnerability and Threat Database: http://www.iss.net/xforce

                   Please send suggestions, updates, and comments to:
                   X-Force <xforce@iss.net> of Internet Security Systems, Inc.

