Forwarded From: X-Force <xforceat_private> -----BEGIN PGP SIGNED MESSAGE----- ISS Vulnerability Alert September 10, 1998 Windows Backdoors Update Synopsis: This advisory is an update of our cDc Back Orifice advisory, which was released August 6, 1998. The following information is new to this advisory: * Information about the NetBus backdoor that works on Windows 95/98 and NT. * A backdoor in NetBus and how to remove the program. * Dramatic increase in backdoor compromises since the release of Back Orifice. * New enhancements to Back Orifice that help hackers, and availability of additional tools to detect and remove Back Orifice. * The BoSniffer trojan horse. 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. Internet Security Systems (ISS) RealSecure 2.5 will detect and notifyyou of any Back Orifice activity on your network, regardless of the port it's using. There is also a program available on the Internet called NetBus, with functionality similar to BO, and in some ways more advanced than BO. NetBus has been available, but its widespread use as a hacking tool has not occurred until recently. Unlike BO, NetBus will run on Windows 95/98 and NT. Since the release of Back Orifice, ISS X-Force has noticed an increase of machines that have been compromised. Over the past few weeks, there have been many machines announcing that they are compromised in the #bo_owned channel on the Efnet IRC network. ISS X-Force has received over fifty e-mails asking for help because machines have been compromised with BO or NetBus. Description: A backdoor is a program that is designed to hide itself inside a target host. It allows 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 BO 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. NetBus, available at http://members.spree.com/NetBus/index.html, allows the remote user to do most of the functions BO can do, as well as open/close the CD-ROM drive, send interactive dialogs to chat with the compromised system,listen to the system's microphone (if it has one), and a few other features. The web page listed above has information about all of NetBus's capabilities. The page also contains instructions for removing NetBus from your system. 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. 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 files that may not have been intentionally installed on the machine. If the length of one of these files is close to 124,928 (give or take 30 bytes) then it is probably Back Orifice. You can also use the netstat program that comes with Windows to check if the system is vulnerable. 'netstat -an' will list all connected and listening ports, so you can see if there are any open UDP ports that shouldn't be open, and take corrective action. Here is some sample output from netstat: C:\WINDOWS>netstat -an | find "UDP" UDP 0.0.0.0:31337 *:* In this example, you can see a UDP service listening on port 31337. This service is Back Orifice. It doesn't have to be on port 31337, so if you see anything else that looks suspicious, check your registry. More information about BO can be obtained from the cDc web page at http://www.cultdeadcow.com. More information about detection and removal of BO can be found at http://www.nwi.net/~pchelp/bo.html. Determining if NetBus has been installed on your machine: NetBus uses TCP for communication, and always uses ports 12345 and 12346 for listening for connections. netstat will tell you if NetBus is installed if you issue the command 'netstat -an | find "12345"'. Then, start the windows 'telnet' program and connect to 'localhost' at port 12345. If NetBus is installed, a string similar to 'NetBus 1.53' or 'NetBus 1.60 x' will be displayed when you connect. NetBus's protocol is not encrypted and the commands have a simple format: the name of the command, followed by a semicolon, followed by the arguments separated by semicolons. It is possible to set a password on the NetBus server, and the password is stored in the registry as plaintext at HKEY_CURRENT_USER\Patch\Settings\ServerPwd. X-Force has discovered that there is a backdoor in NetBus that will allow anyone to connect with no password. When the client sends the password to the server, it sends a string similar to 'Password;0;my_password'. If the client uses a 1 instead of a 0, you will be authenticated with any password. By default, the NetBus server is called 'Patch.exe', but it can be renamed. 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 act according to your site security policy. There are two ways to remove NetBus, depending on what version you use: - - For versions 1.5x, the instructions to remove NetBus are located at http://members.spree.com/NetBus/remove_1.html. - - For version 1.6, the removal instructions are at http://members.spree.com/NetBus/remove_2.html. You can remove any installation of NetBus 1.6 by telneting to the machine at port 12345, typing 'Password;1;', pressing enter, typing 'RemoveServer;1', and pressing enter. You will be disconnected, NetBus will be disabled and will longer run at startup. You will have to delete Patch.exe from you Windows directory if you want to completely remove NetBus. This procedure works even if there is a password set, however it doesn't work with the 1.5x versions. Determining the password and configuration of an installed BO: 1. Using a text editor such as notepad, view the server exe file. 2. If the last line of the file is '88$8(8,8084888<8@8D8H8L8P8T8X8\8'8d8h8l8', then the server is using the default configuration. Otherwise, the configuration will be present on the last several lines of this file, in this order: <filename> <service description> <port number> <password> <optional plugin information> Back Orifice plugins: There are several plugin applications for BO, called 'BUTTplugs' by cDc, which are used to enhance the functionality of BO. Currently there are four plugins available on the cDc page (http://www.cultdeadcow.com/tools/bo_plugins.html). These plugins will e-mail the attacker when someone installs their copy of BO, or access Internet Relay Chat (IRC) to join a channel and notify them that BO is installed. There is also a plugin used to embed BO into any program you wish, which makes it easier to fool a user into running it. The currently available plugins are: Speakeasy - An IRC plugin that secretly logs into a predefined server and broadcasts the host's IP address Silk Rope - Binds Back Orifice to almost any existing program. Saran Wrap - Hides Back Orifice in an existing standard "InstallShield" installer program Butt Trumpet - Sends the attacker an email with the host's IP address, after BO is installed Trojaned BO detector program: There is a program called BoSniffer that is distributed on the Internet and claims to detect and remove BO from your system. This is actually Back Orifice, and you should not use this program. Be wary of any fixes for BO from untrusted sources. This fix has been distributed with the filenames bosniffer.exe and bosniffer.zip. 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. NetBus provides an richer feature set than BO, works on Windows NT, but is easier to detect than BO since it will always use TCP port 12345 and provides a banner with the NetBus version when you connect via telnet. - ---------- 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 xforceat_private 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 <xforceat_private> of Internet Security Systems, Inc. -----BEGIN PGP SIGNATURE----- Version: 2.6.3a Charset: noconv iQCVAwUBNfgxejRfJiV99eG9AQGAlwP+PDwP75n3cWHWEVPM6Beg6fHA1ekuvwG+ +27uZjPg6ZKViBONwGcIh6+IKtVVXY3tcorXAu9Pz7c5cTwYgaZQ6Fzztn/xg0wv 4iNAitfaGvXm9F8J7VAMK3tVG9HR0Hn5ZSxH9taZmDP0ReZoxRlar5gqVtG8D3TX DGW3ABrY5hc= =4AmX -----END PGP SIGNATURE----- -o- Subscribe: mail majordomoat_private with "subscribe isn". Today's ISN Sponsor: Repent Security Incorporated [www.repsec.com]
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