Trojan.Webus.C

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Discovered: October 12, 2004
Updated: February 13, 2007 12:28:20 PM
Type: Trojan Horse
Systems Affected: Windows


Trojan.Webus.C is a Trojan horse that connects to an Internet Relay Chat (IRC) server and opens a backdoor on TCP port 10888 or 1080.

Antivirus Protection Dates

  • Initial Rapid Release version October 12, 2004
  • Latest Rapid Release version September 28, 2010 revision 054
  • Initial Daily Certified version October 12, 2004
  • Latest Daily Certified version September 28, 2010 revision 036
  • Initial Weekly Certified release date October 12, 2004

Click here for a more detailed description of Rapid Release and Daily Certified virus definitions.

Writeup By: Candid Wueest

Discovered: October 12, 2004
Updated: February 13, 2007 12:28:20 PM
Type: Trojan Horse
Systems Affected: Windows


When Trojan.Webus.C is executed, it performs the following actions:

  1. Attempts to create a mutex named 3286E64A-W325-121E-BFC6-083C2BE2S511 to ensure that only one instance is running.

  2. Copies itself as %System%\Lassa.exe.

    Note: %System% is a variable that refers to the System folder. By default this is C:\Windows\System (Windows 95/98/Me), C:\Winnt\System32 (Windows NT/2000), or C:\Windows\System32 (Windows XP).

  3. Adds the value:

    ".mscdr" = "%System%\lassa.exe"


    to the following registry key, which loads the Trojan when Windows starts:

    HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run


    Note: This is not %System% that refers to the directory \WINNT\System32. This threat copies the file System\Lassa.exe into the \WINNT\System (at least on Windows 2000).

  4. Opens a back door on TCP port 10888 or 1080 and waits for incoming connections. This may allow an attacker to use the infected computer as a proxy server to another host.

  5. Connects to a predetermined IRC server on TCP port 8080 and waits for commands from an attacker.


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.

Writeup By: Candid Wueest

Discovered: October 12, 2004
Updated: February 13, 2007 12:28:20 PM
Type: Trojan Horse
Systems Affected: Windows


The following instructions pertain to all current and recent Symantec antivirus products, including the Symantec AntiVirus and Norton AntiVirus product lines.

Important: On computers running Norton AntiVirus 2005 or later, the QuickScan tool will automatically search for and remove malicious threats when new virus definitions are downloaded. While every effort has been made to ensure that the QuickScan tool removes all the traces of a malicious threat from an infected computer, we advise that you confirm that all the files and registry entries have been removed. We recommend following the manual removal steps and deleting any threat-related files or registry entries remaining on the computer.

  1. Disable System Restore (Windows Me/XP).
  2. Update the virus definitions.
  3. Restart the computer in Safe mode or end the malicious process.
  4. Run a full system scan and delete all the files detected as Trojan.Webus.C.
  5. Delete the value that was added to the registry.
For specific details on each of these steps, read the following instructions.

1. To disable System Restore (Windows Me/XP)
If you are running Windows Me or Windows XP, we recommend that you temporarily turn off System Restore. Windows Me/XP uses this feature, which is enabled by default, to restore the files on your computer in case they become damaged. If a virus, worm, or Trojan infects a computer, System Restore may back up the virus, worm, or Trojan on the computer.

Windows prevents outside programs, including antivirus programs, from modifying System Restore. Therefore, antivirus programs or tools cannot remove threats in the System Restore folder. As a result, System Restore has the potential of restoring an infected file on your computer, even after you have cleaned the infected files from all the other locations.

Also, a virus scan may detect a threat in the System Restore folder even though you have removed the threat.

For instructions on how to turn off System Restore, read your Windows documentation, or one of the following articles:

Note:
After you have completed the removal procedure and are satisfied that the threat has been removed, re-enable System Restore by following the instructions in the previously mentioned documents.

For additional information, and an alternative to disabling Windows Me System Restore, see the Microsoft Knowledge Base article, "Antivirus Tools Cannot Clean Infected Files in the _Restore Folder ," Article ID: Q263455.

2. To update the virus definitions
Symantec Security Response fully tests all the virus definitions for quality assurance before they are posted to our servers. There are two ways to obtain the most recent virus definitions:
3. To restart the computer in Safe mode or end the malicious process

To restart the computer in Safe mode in Windows 95/98/Me
Shut down the computer and turn off the power. Wait for at least 30 seconds, and then restart the computer in Safe mode. For instructions, read "How to start the computer in Safe Mode ."

To end the malicious process in Windows NT/2000/XP
  1. Press Ctrl+Alt+Delete once.
  2. Click Task Manager.
  3. On the Processes tab, double-click the Image Name column header to alphabetically sort the processes.
  4. Scroll through the list, and look for Lassa.exe.
  5. If you find the file, click it, and then click End Process.
  6. Exit the Task Manager.

4. To scan for and delete the infected files
  1. Start your Symantec antivirus program and make sure that it is configured to scan all the files.
  2. Run a full system scan.
  3. If any files are detected as infected with Trojan.Webus.C, click Delete.


    Note:
    If your Symantec antivirus product reports that it cannot delete an infected file, Windows may be using the file. To fix this, run the scan in Safe mode. For instructions, read "How to start the computer in Safe Mode." After you have restarted the computer in Safe mode, run the scan again.

    After you delete the files, you may leave the computer in Safe mode and proceed with section 5. After you have finished step 5, restart the computer in Normal mode.

5. To delete the value from the registry

Important:
Symantec strongly recommends that you back up the registry before making any changes to it. Incorrect changes to the registry can result in permanent data loss or corrupted files. Modify the specified keys only. Read the document, "How to make a backup of the Windows registry ," for instructions.
  1. On the Windows taskbar, click Start > Run.
  2. Type the following:

    regedit

  3. Click OK.

  4. Navigate to the following key:

    HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run

  5. In the right pane, delete the following value:

    ".mscdr" = "%System%\lassa.exe"

  6. Exit the Registry Editor.


Writeup By: Candid Wueest