W32.Opaserv.AE.Worm

1. Attempts to create a mutex named 4wsDosFDPS! and exits if the mutex already exists. This ensures that only one instance of the worm is running on the computer.
   
   
2. Registers itself as a service process.
   
   
3. Lowers its priority so that it runs only when the system is otherwise idle.
   
   
4. Copies itself as %Windir%\Natal.scr.
   
   

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   Note: %Windir% is a variable. The worm locates the Windows installation folder (by default, this is C:\Windows on Windows 95/98/Me) and copies itself to that location.

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5. Checks for the value:
   
   Natal!Old
   
   in the registry key:
   
   HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Run
   
   
6. If the value exists, the worm deletes the file to which the Natal!Old value points.
   
   
7. If the Natal!Old value does not exist, then the worm will determine whether the value:
   
   Natal
   
   exists in the registry key:
   
   HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Run
   
   
8. If the value does not exist, the worm will add the value:
   
   "Natal"="%Windir%\Natal.scr"
   
   to that registry key.
   
   
9. Creates the file named C:\lammer!, which contains the text:
   
   run=c:\windows\natal.scr
   
   
10. Attempts to contact a predetermined Web site, probably to update itself. The Web site was inactive at the time of this writing.
    
    
11. Uses a security vulnerability in Microsoft Windows 95/98/Me to spread to other computers. The worm sends single-character passwords to network shares, attempting to get access to other Windows 95/98/Me file shares without knowing the entire password. The affected systems include:
    
    • Microsoft Windows 95
    • Microsoft Windows 98
    • Microsoft Windows 98 Second Edition
    • Microsoft Windows Me
      
      

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      Note: A patch for computers that are running these operating systems can be found in the Microsoft Security Bulletin MS00-072.

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12. Attempts to copy itself as Natal.scr to vulnerable network shares.
    
    
13. Modifies the[windows]section of the %Windir%\Win.ini file by adding one of the following lines:
    
    • run= c:\windows\natal.scr
    • run= c:\lammer!
      
      so that Windows 95/98/Me-based computers will run the worm each time you start Windows.

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.