W95.Tenrobot

If a file infected with W95.Tenrobot is executed under Windows NT 4/2000/ XP, the virus will not do anything except directly transfer control to the original host.

When W95.Tenrobot is executed under Windows 95/98/Me, it creates a separate worker thread to execute the remainder of its functionality. Then, it directly transfers control to the original host program.

Worker thread
This thread performs two functions:

• Hooks the file system open request. (Refer to the section, "Hooked file system," for more information.)
• Establishes a backdoor connection to an IRC channel.

The first thing this thread does is copy W95.Tenrobot to shared memory and hook the file system open request. (Refer to the section, "Hooked file system," for more information.)

Then this thread will try to connect to an IRC server, using port 6667.

This server is located on 217.17.33.10 and is currently registered to irc.efnet.pl.

Then, W95.Tenrobot will register itself with the server using a random User name and Nick.

If a successful connection is established, W95.Tenrobot will connect to the IRC channel #NetRobot where it will wait for further commands.

Backdoor functionality
W95.Tenrobot provides the following set of rudimentary remote control commands that a remote hacker could use.

• The supported IRC-specific commands are:
  • JOIN
  • KICK
  • PING
  • PRIVMSG, which the Backdoor uses to carry out specific actions on the local system.
  • The message, !die: If the hacker sends the message !die, the virus will unhook itself from the file system and terminate the backdoor functionality.
• Local system specific commands using PRIVMSG.
• Ability to unhook itself from memory and terminate the backdoor.
• Ability to download and execute a program from a remote Internet site using HTTP (on port 80).

Hooked file system

NOTE: The hooking file system process is performed by hooking an undocumented API in the kernel, not by using the standard IFS hook.

Once in memory, W95.Tenrobot will infect all the opened files with a .exe extension, excluding any file in which the first eight letters match "PSTORES."

Recommendations

Symantec Security Response encourages all users and administrators to adhere to the following basic security "best practices":

• Use a firewall to block all incoming connections from the Internet to services that should not be publicly available. By default, you should deny all incoming connections and only allow services you explicitly want to offer to the outside world.
• Enforce a password policy. Complex passwords make it difficult to crack password files on compromised computers. This helps to prevent or limit damage when a computer is compromised.
• Ensure that programs and users of the computer use the lowest level of privileges necessary to complete a task. When prompted for a root or UAC password, ensure that the program asking for administration-level access is a legitimate application.
• Disable AutoPlay to prevent the automatic launching of executable files on network and removable drives, and disconnect the drives when not required. If write access is not required, enable read-only mode if the option is available.
• Turn off file sharing if not needed. If file sharing is required, use ACLs and password protection to limit access. Disable anonymous access to shared folders. Grant access only to user accounts with strong passwords to folders that must be shared.
• Turn off and remove unnecessary services. By default, many operating systems install auxiliary services that are not critical. These services are avenues of attack. If they are removed, threats have less avenues of attack.
• If a threat exploits one or more network services, disable, or block access to, those services until a patch is applied.
• Always keep your patch levels up-to-date, especially on computers that host public services and are accessible through the firewall, such as HTTP, FTP, mail, and DNS services.
• Configure your email server to block or remove email that contains file attachments that are commonly used to spread threats, such as .vbs, .bat, .exe, .pif and .scr files.
• Isolate compromised computers quickly to prevent threats from spreading further. Perform a forensic analysis and restore the computers using trusted media.
• Train employees not to open attachments unless they are expecting them. Also, do not execute software that is downloaded from the Internet unless it has been scanned for viruses. Simply visiting a compromised Web site can cause infection if certain browser vulnerabilities are not patched.
• If Bluetooth is not required for mobile devices, it should be turned off. If you require its use, ensure that the device's visibility is set to "Hidden" so that it cannot be scanned by other Bluetooth devices. If device pairing must be used, ensure that all devices are set to "Unauthorized", requiring authorization for each connection request. Do not accept applications that are unsigned or sent from unknown sources.
• For further information on the terms used in this document, please refer to the Security Response glossary.

Summary