Backdoor.Rtkit.B

SUMMARY

Backdoor.Rtkit.B is a backdoor server program that allows a remote attacker to perform various actions on an infected computer. This backdoor attempts to mask its presence by hiding files, processes, and registry entries.

Protection

• Virus Definitions (LiveUpdate™ Weekly) October 6, 2004
• Virus Definitions (Intelligent Updater) October 1, 2004

Threat Assessment

Wild

• Wild Level: Low
• Number of Infections: 0 - 49
• Number of Sites: 0 - 2
• Geographical Distribution: Low
• Threat Containment: Easy
• Removal: Easy

Damage

• Damage Level: Low
• Compromises Security Settings: Opens a backdoor.

Distribution

• Distribution Level: Low
• Ports: TCP port 445

TECHNICAL DETAILS

When Backdoor.Rtkit.B is installed, it performs the following actions:

1. Reads configuration data from a file named ntbackdoor.ini, and then deletes this file.
   
   
2. Creates the following files:
   
   • %System%comsserver trootkit.exe
   • %System%comsserverglobalc.dll
   • %System%comsserver pf.sys
   • %System%comsservertkit.log
     
     Note:
   • The directory and filenames can be changed in the configuration file.
   • %System% is a variable that refers to the System folder. By default, this is C:WindowsSystem (Windows 95/98/Me), C:WinntSystem32 (Windows NT/2000), or C:WindowsSystem32 (Windows XP).
     
     
3. Creates the following registry entries:
   
   HKEY_LOCAL_MACHINESYSTEMCurrentControlSetEnumRootLEGACY_RTKIT
   HKEY_LOCAL_MACHINESYSTEMCurrentControlSetEnumRootLEGACY_NPF
   HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesROOTKIT1
   HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesNPF
   HKEY_LOCAL_MACHINESOFTWARERtKit
   
   
4. Opens a backdoor and allows connections from the remote attacker using one of four methods: TCP, UDP, ICMP, or user defined. By default, the backdoor uses TCP port 445 for communications.
   
   The back door allows the remote attacker to perform some of the following actions on the infected computer:
   
   • Hide or unhide files, directories, processes, registry keys and values, users, or services.
   • Upload and download files to and from the compromised system.
   • Log keystrokes.
   • Initiate a Denial of Service (DoS) attack.
   • Change passwords.
   • List and terminate processes.
   • Restart the system.
   • Open a remote command prompt.
   • Get system information.

Recommendations

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

• Turn off and remove unneeded services. By default, many operating systems install auxiliary services that are not critical, such as an FTP server, telnet, and a Web server. These services are avenues of attack. If they are removed, blended threats have less avenues of attack and you have fewer services to maintain through patch updates.
• If a blended 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 (for example, all Windows-based computers should have the current Service Pack installed.). Additionally, please apply any security updates that are mentioned in this writeup, in trusted Security Bulletins, or on vendor Web sites.
• 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.
• Configure your email server to block or remove email that contains file attachments that are commonly used to spread viruses, such as .vbs, .bat, .exe, .pif and .scr files.
• Isolate infected computers quickly to prevent further compromising your organization. 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.

REMOVAL

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. To restart the computer in Safe mode or VGA mode.
4. Run a full system scan and delete all the files detected as Backdoor.Rtkit.B.
5. Delete the value that was added to the registry.
6. Delete the folder, %System%comsserver.
   

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:

• "How to disable or enable Windows Me System Restore"
• "How to turn off or turn on Windows XP System Restore"

Note: When you are completely finished with the removal procedure and are satisfied that the threat has been removed, re-enable System Restore by following the instructions in the aforementioned 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:

• Running LiveUpdate, which is the easiest way to obtain virus definitions: These virus definitions are posted to the LiveUpdate servers once each week (usually on Wednesdays), unless there is a major virus outbreak. To determine whether definitions for this threat are available by LiveUpdate, refer to the Virus Definitions (LiveUpdate).
• Downloading the definitions using the Intelligent Updater: The Intelligent Updater virus definitions are posted daily. You should download the definitions from the Symantec Security Response Web site and manually install them. To determine whether definitions for this threat are available by the Intelligent Updater, refer to the Virus Definitions (Intelligent Updater).
  
  The Intelligent Updater virus definitions are available: Read "How to update virus definition files using the Intelligent Updater" for detailed instructions.

3. To restart the computer in Safe mode or VGA mode

Shut down the computer and turn off the power. Wait for at least 30 seconds, and then restart the computer in Safe mode or VGA mode.

• For Windows 95, 98, Me, 2000, or XP users, restart the computer in Safe mode. For instructions, read the document, "How to start the computer in Safe Mode."
• For Windows NT 4 users, restart the computer in VGA mode.
  

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.
   • For Norton AntiVirus consumer products: Read the document, "How to configure Norton AntiVirus to scan all files."
   • For Symantec AntiVirus Enterprise products: Read the document, "How to verify that a Symantec Corporate antivirus product is set to scan all files."
2. Run a full system scan.
3. If any files are detected as infected with Backdoor.Rtkit.B, 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 the document, "How to start the computer in Safe Mode." Once you have restarted in Safe mode, run the scan again.
   
   (After the files are deleted, you can leave the computer in Safe mode and proceed with section 4. When that is done, 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. Click Start > Run.
2. Type regedit
   
   Then click OK.
   
   
3. Navigate to and delete the keys:
   
   HKEY_LOCAL_MACHINESYSTEMCurrentControlSetEnumRootLEGACY_RTKIT
   HKEY_LOCAL_MACHINESYSTEMCurrentControlSetEnumRootLEGACY_NPF
   HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesROOTKIT1
   HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesNPF
   HKEY_LOCAL_MACHINESOFTWARERtKit
   
   
4. Exit the Registry Editor.

6. To delete the folder, %System%comsserver

a. Open Explorer

b. Navigate to and delete the following folder:

%System%comsserver