Backdoor.Fuwudoor

SUMMARY

Backdoor.Fuwudoor is a back door Trojan that allows unauthorized access to a compromised computer and attempts to hide its presence.

Note: Definitions dated prior to May 23, 2005 detect this threat as Backdoor.Lingosky.

Protection

• Virus Definitions (LiveUpdate™ Weekly) March 23, 2005
• Virus Definitions (Intelligent Updater) March 23, 2005

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
• Payload: Opens a back door.

Distribution

• Distribution Level: Low

TECHNICAL DETAILS

Once executed, Backdoor.Fuwudoor performs the following actions:

1. Drops one or more of the following files:
   
   
   • %System%ipsec.dll
   • %System%appmgmt.dll
   • %System%rowsvr.dll
   • %System% rkw.dll
   • %System% rks.dll
   • %System%kdc.dll
   • %System%dmsrv.dll
   • %System%mesg.dll
   • %System% etlogin.dll
   • %System%protstrg.dll
   • %System%lmhosts.dll
   • %System%w32t.dll
   • %System% tms.dll
     
     Note: %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).
     
     
2. Registers the dropped .dll file as a service that may already exist on the computer, by modifying some service properties.
   
   Note: It may be difficult to notice the modifications to the existing services as the descriptions are not changed and the path to the executable is similar to the legitimate one. In this way the Trojan attempts to hide its presence on the compromised computer.
   
   
3. Registers one or more of the following services:
   
   Display name: ProtectedStorage
   Path to executable: %Windir%system32svchost.exe -k ProtectedStorage
   
   Display name: Messenger
   Path to executable: %Windir%system32svchost.exe -k Messenger
   
   Display name: Policy Agent
   Path to executable: %Windir%system32svchost.exe -k Policy Agent
   
   Display name: AppMgmt
   Path to executable: %Windir%system32svchost.exe -k AppMgmt
   
   Display name: Browser
   Path to executable: %Windir%system32svchost.exe -k Browser
   
   Display name: TrkWks
   Path to executable: %Windir%system32svchost.exe -k TrkWks
   
   Display name: TrkSvr
   Path to executable: %Windir%system32svchost.exe -k TrkSvr
   
   Display name: kdc
   Path to executable: %Windir%system32svchost.exe -k kdc
   
   Display name: dmserver
   Path to executable: %Windir%system32svchost.exe -k dmserver
   
   Display name: NetLogon
   Path to executable: %Windir%system32svchost.exe -k NetLogon
   
   Display name: LmHosts
   Path to executable: %Windir%system32svchost.exe -k LmHosts
   
   Display name: W32Time
   Path to executable: %Windir%system32svchost.exe -k W32Time
   
   Display name: ntmssvc
   Path to executable: %Windir%system32svchost.exe -k ntmssvc
   
   Note: %Windir% is a variable that refers to the Windows installation folder. By default, this is C:Windows or C:Winnt.
   
   
4. Adds the value:
   
   "ServiceDll" = "%Windir%system32 tms.dll"
   
   to the registry subkey:
   
   HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServices tmssvcParameters
   
   
5. Adds the value:
   
   "ServiceDll" = "%Windir%system32w32t.dll"
   
   to the registry subkey:
   
   HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesW32TimeParameters
   
   
6. Adds the value:
   
   "ServiceDll" = "%Windir%system32lmhosts.dll"
   
   to the registry subkey:
   
   HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesLmHostsParameters
   
   
7. Adds the value:
   
   "ServiceDll" = "%Windir%system32 etlogin.dll"
   
   to the registry subkey:
   
   HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesNetLogonParameters
   
   
8. Adds the value:
   
   "ServiceDll" = "%Windir%system32dmsrv.dll"
   
   to the registry subkey:
   
   HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesdmserverParameters
   
   
9. Adds the value:
   
   "ServiceDll" = "%Windir%system32kdc.dll"
   
   to the registry subkey:
   
   HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServiceskdcParameters
   
   
10. Adds the value:
    
    "ServiceDll" = "%Windir%system32 rks.dll"
    
    to the registry subkey:
    
    HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesTrkSvrParameters
    
    
11. Adds the value:
    
    "ServiceDll" = "%Windir%system32 rkw.dll"
    
    to the registry subkey:
    
    HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesTrkWksParameters
    
    
12. Adds the value:
    
    "ServiceDll" = "%Windir%system32rowsvr.dll"
    
    to the registry subkey:
    
    HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesBrowserParameters
    
    
13. Adds the value:
    
    "ServiceDll" = "%Windir%system32appmgmt.dll"
    
    to the registry subkey:
    
    HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesAppMgmtParameters
    
    
14. Adds the value:
    
    "ServiceDll" = "%Windir%system32ipsec.dll"
    
    to the registry subkey:
    
    HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesPolicyAgentParameters
    
    
15. Adds the value:
    
    "ServiceDll" = "%Windir%system32mesg.dll"
    
    to the registry subkey:
    
    HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesMessengerParameters
    
    
16. Adds the value:
    
    "ServiceDll" = "%Windir%system32protstrg.dll"
    
    to the registry subkey:
    
    HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesProtectedStorageParameters
    
    
17. Creates the following driver file in an attempt to hide the activities of the back door on the network:
    
    %System%Driversusb2.sys
    
    
18. Adds the value:
    
    "ImagePath" = "system32Driversusb2.sys"
    
    to the registry subkey:
    
    HKEY_LOCAL_MACHINESystemCurrentControlSetServicesusb2
    
    
19. Contacts a server on the winupdate.myserver.com domain, and notifies it of its existence.
    
    
20. Opens a back door on the compromised computer and may allow a remote attacker to perform the following activities:
    
    
    • Send GET or POST requests to a HTTP server
    • Show or terminate running processes or threads
    • Execute commands

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.

1. Disable System Restore (Windows Me/XP).
2. Update the virus definitions.
3. Restart the computer in Safe mode or VGA mode.
4. Run a full system scan and delete all the files detected as Backdoor.Fuwudoor.
5. Reverse the changes made to the registry.
   

For 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.Fuwudoor, click Delete.
4. If you are still in Safe mode, restart the computer in Normal mode before proceeding to the next section. For instructions, read the section on returning to Normal mode in the document: How to start the computer in Safe Mode.

5. To reverse the changes made to 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 subkeys 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 the subkey:
   
   HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServices tmssvcParameters
   
   
4. In the right pane, delete the value:
   
   "ServiceDll" = "%Windir%system32 tms.dll"
   
   
5. Navigate to the subkey:
   
   HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesW32TimeParameters
   
   
6. In the right pane, delete the value:
   
   "ServiceDll" = "%Windir%system32w32t.dll"
   
   
7. Navigate to the subkey:
   
   HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesLmHostsParameters
   
   
8. In the right pane, delete the value:
   
   "ServiceDll" = "%Windir%system32lmhosts.dll"
   
   
9. Navigate to the subkey:
   
   HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesNetLogonParameters
   
   
10. In the right pane, delete the value:
    
    "ServiceDll" = "%Windir%system32 etlogin.dll"
    
    
11. Navigate to the subkey:
    
    HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesdmserverParameters
    
12. In the right pane, delete the value:
    
    "ServiceDll" = "%Windir%system32dmsrv.dll"
    
    
13. Navigate to the subkey:
    
    HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServiceskdcParameters
    
    
14. In the right pane, delete the value:
    
    "ServiceDll" = "%Windir%system32kdc.dll"
    
    
15. Navigate to the subkey:
    
    HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesTrkSvrParameters
    
    
16. In the right pane, delete the value:
    
    "ServiceDll" = "%Windir%system32 rks.dll"
    
    
17. Navigate to the subkey:
    
    HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesTrkWksParameters
    
    
18. In the right pane, delete the value:
    
    "ServiceDll" = "%Windir%system32 rkw.dll"
    
    
19. Navigate to the subkey:
    
    HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesBrowserParameters
    
    
20. In the right pane, delete the value:
    
    "ServiceDll" = "%Windir%system32rowsvr.dll"
    
    
21. Navigate to the subkey:
    
    HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesAppMgmtParameters
    
    
22. In the right pane, delete the value:
    
    "ServiceDll" = "%Windir%system32appmgmt.dll"
    
    
23. Navigate to the subkey:
    
    HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesPolicyAgentParameters
    
    
24. In the right pane, delete the value:
    
    "ServiceDll" = "%Windir%system32ipsec.dll"
    
    
25. Navigate to the subkey:
    
    HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesMessengerParameters
    
    
26. In the right pane, delete the value:
    
    "ServiceDll" = "%Windir%system32mesg.dll"
    
    
27. Navigate to the subkey:
    
    HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesProtectedStorageParameters
    
    
28. In the right pane, delete the value:
    
    "ServiceDll" = "%Windir%system32protstrg.dll"
    
    
29. Navigate to the subkey:
    
    HKEY_LOCAL_MACHINESystemCurrentControlSetServicesusb2
    
    
30. In the right pane, delete the value:
    
    "ImagePath" = "system32Driversusb2.sys"
    
    
31. Exit the Registry Editor.