Backdoor.Nibu

SUMMARY

The Backdoor.Nibu is a Trojan Horse that allows unauthorized access to an infected computer. The Trojan opens TCP port 1000, 1001, and 2283 to allow for remote access. It also attempts to steal confidential information by logging keystrokes and copying Windows password files.

Protection

• Virus Definitions (LiveUpdate™ Weekly) July 30, 2003
• Virus Definitions (Intelligent Updater) July 30, 2003

Threat Assessment

Wild

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

Damage

• Damage Level: Medium
• Releases Confidential Info: Logs keystrokes. Steals Windows password files.
• Compromises Security Settings: Allows unauthorized remote access to an infected computer.

Distribution

• Distribution Level: Low
• Ports: 1000, 1001, and 2283

TECHNICAL DETAILS

When Backdoor.Nibu is executed, it performs the following actions:

1. Copies itself to the following folders:
   
   • %Windows%Dllreg.exe
   • %System%Vxdmgr32.exe
   • %System%Load32.exe
   • %Startup%Rundllw.exe
     
     NOTES:
     • %Windows% is a variable. The Trojan locates the Windows installation folder (by default, this is C:Windows or C:Winnt) and copies itself to that location.
     • %System% is a variable. The worm locates the System folder and copies itself to that location. By default, this is C:WindowsSystem (Windows 95/98/Me), C:WinntSystem32 (Windows NT/2000), or C:WindowsSystem32 (Windows XP).
     • %Startup% is a variable. The worm locates the Windows Startup folder, which the current user uses, and copies the files to that location.
       
       
2. Drops the following files:
   
   • %Windows%Windrive.exe
   • %Windows%Guid32.dll, detected as Keylogger.Trojan
     
     and executes Windrive.exe.
     
     
3. Adds the value:
   
   "load32" = "%System%load32.exe"
   
   to the registry key:
   
   HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindowsCurrentVersionRun
   
   
4. Modifies the Win.ini file to include:
   
   run=%Windows%dllreg.exe
   
   
5. Rewrites the shell line of System.ini:
   
   shell=explorer.exe %System%vxdmgr32.exe
   
   
6. Connects to an IRC channel on a specific IRC server.
   
   
7. Opens ports 1000, 1001, and 2283 for connections from the creator of the Trojan.
   
   
8. Also does following:
   
   • Logs key strokes
   • Steals WebMoney information
   • Steals clipboard data
   • Steals ICQ information
   • Creates a process log, Vxdload.log, in the %Windir% folder
   • Steals PWL files
   • Sends stolen information to specific email addresses
   • Opens/closes the CD-ROM drive
   • Plays a .Wav file

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. Run a full system scan and delete all the files detected as Backdoor.Nibu or Keylogger.Trojan.
4. Delete the value that was added to the registry.
5. Edit the Win.ini and System.ini files
   

For specific details on each of these steps, read the following instructions.

1. Disabling 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"

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. Updating 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 on U.S. business days (Monday through Friday). 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. Scanning for and deleting 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.Nibu or Keylogger.Trojan, click Delete.
4. Using Windows Explorer, navigate to the %Windir% directory and delete the dxdload.log file.

4. Deleting the value from the registry

CAUTION: 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, and then click Run. (The Run dialog box appears.)
2. Type regedit
   
   Then click OK. (The Registry Editor opens.)
   
   
3. Navigate to the key:
   
   HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindowsCurrentVersionRun
   
   
4. In the right pane, delete the value:
   
   "load32" = "%System%load32.exe"
   
   
5. Exit the Registry Editor.

5. Editing the Win.ini and System.ini files
If you are running Windows 95/98/Me, follow these steps:

1. The function you perform depends on your operating system:
   • Windows 95/98: Go to step b.
   • Windows Me: If you are running Windows Me, the Windows Me file-protection process may have made a backup copy of the Win.ini and System files that you need to edit. If this backup copy exists, it will be in the C:WindowsRecent folder. Symantec recommends that you delete this file before continuing with the steps in this section. To do this:
     1. Start Windows Explorer.
     2. Browse to and select the C:WindowsRecent folder.
     3. In the right pane, select the Win.ini file and delete it. The Win.ini file will be regenerated when you save your changes to it in step f.
        
        
2. Click Start, and then click Run.
3. Type the following, and then click OK.
   
   edit c:windowswin.ini
   
   (The MS-DOS Editor opens.)
   
   NOTE: If Windows is installed in a different location, make the appropriate path substitution.
   
   
4. In the [windows] section of the file, look for a line similar to:
   
   run=%Windir%dllreg.exe
   
   
5. If this line exists, delete
   
   %Windir%dllreg.exe
   
   
6. Click File, and then click Save.
7. Click File, and then click Exit.
8. Click Start, and then click Run.
9. Type the following, and then click OK.
   
   edit c:windowssystem.ini
   
   (The MS-DOS Editor opens.)
   
   NOTE: If Windows is installed in a different location, make the appropriate path substitution.
   
   
10. In the [boot] section of the file, look for a line similar to:
    
    shell=explorer.exe %System%vxdmgr32.exe
    
    
11. If this line exists, delete everything to the right of Explorer.exe.
    
    When you are done, it should look like:
    
    shell = Explorer.exe
    
    
12. Click File, and then click Save.
13. Click File, and then click Exit.