W32.Nimos.Worm

SUMMARY

W32.Nimos.Worm is a network-aware worm that captures keystrokes and passwords, and then sends them to the attacker.

This worm is written in Microsoft Visual Basic and is packed with PEBundle and ExeStealth.

Protection

• Virus Definitions (LiveUpdate™ Weekly) March 18, 2004
• Virus Definitions (Intelligent Updater) March 18, 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

Distribution

• Distribution Level: Low

TECHNICAL DETAILS

When the worm is executed, it does following:

1. Copies itself as %Windows%SystemLsass.exe.
   
   

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   Note: %Windir% is a variable. The W32.Nimos.Worm locates the Windows installation folder (by default, this is C:Windows or C:Winnt) and copies itself to that location.

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2. Creates the following files:
   • %Windir%Ocxtodll.exe.
   • %System%Msinet.ocx
   • %System%Vbs6stkit.dll
   • %System%Mswinsck.ocx
     
     All of these files are not malicious, and therefore, Symantec antivirus products do not detect them.
     
     
3. Attempts to copy itself to the following folders on remote computers:
   • WindowsStart MenuProgramsStartup
   • WindowsMenu D.marrerProgrammesD.marrage
   • WindowsMen.InicioProgramasInicio
   • WindowsMen.IniciProgramesIniciaci
   • WinntProfilesAll UsersStart MenuProgramsStartup
   • WinntProfilesAll UsersMen.inicioProgramasInicio
   • WinntProfilesAll UsersMenu D.marrerProgrammesD.marrage
   • WinntProfilesAdministratorStart MenuProgramsStartup
   • WinntProfilesAdministratorMen.inicioProgramasInicio
   • WinntProfilesAdministratorMenu D.marrerProgrammesD.marrage
   • Documents and SettingsAdministratorStart MenuProgramsStartup
   • Documents and SettingsAll UsersStart MenuProgramsStartup
   • Documents and SettingsAll UsersMen.inicioProgramasInicio
   • windows
   • winnt
     
     
4. Adds the value:
   
   "System Handler"="%Windir%SystemLSASS.EXE"
   
   to the registry keys:
   
   HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindowsCurrentVersionRun
   
   HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindowsCurrentVersionRunService
   
   so that the W32.Nimos.Worm runs when you start Windows.
   
   
5. Adds the registry key:
   
   System Handler
   
   under the key:
   
   HKEY_LOCAL_MACHINESoftwareMicrosoftWindowsCurrentVersion
   
   
6. Modifies the default value of the following registry key:
   
   HKEY_CLASSES_ROOTexefileshellopencommand
   
   This causes the worm to execute every time a .exe file is executed.
   
   
7. Attempts to log key strokes and send it to a predetermined email address.

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 W32.Nimos.Worm.
5. Delete the value that was added to the registry.
   

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"

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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.

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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. Restarting 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. 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 W32.Nimos.Worm, click Delete.

5. Deleting the value from the registry

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WARNING: 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.

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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_MACHINESoftwareMicrosoftWindowsCurrentVersionSystem Handler
   
   
4. In the left pane, delete the subkey:
   
   System Handler
   
   
5. Navigate to the key:
   
   HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindowsCurrentVersionRun
   
   
6. In the right pane, delete the value:
   
   "System Handler"="%Windir%SystemLSASS.EXE"
   
   
7. Do one of the following:
   • If you are running Windows NT/2000/XP, proceed to step j.
   • If you are using Windows 95/98/me, proceed to step h.
     
     
8. Navigate to the key:
   
   HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindowsCurrentVersionRunService
   
   
9. In the right pane, delete the value:
   
   "System Handler"="%Windir%SystemLSASS.EXE"
   
   
10. Navigate to the registry key:
    
    HKEY_CLASSES_ROOTexefileshellopencommand
    
    
11. In the right pane, change the default value to: "%1" %*
    
    
12. Exit the Registry Editor.