W32.Welchia.K

When W32.Welchia.K runs, it does the following:

1. Creates the mutex, "WksPatch_Mutex." This mutex allows only one instance of the worm to execute in memory.
   
   
2. Copies itself as %System%\Drivers\Svchost.exe.
   
   

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   Notes:
   • %System% is a variable. The worm locates the System folder and copies itself to that location. By default, this is C:\Windows\System (Windows 95/98/Me), C:\Winnt\System32 (Windows NT/2000), or C:\Windows\System32 (Windows XP).
   • There is a legitimate system file, %System%\Svchost.exe, which has the same file size as the worm on Windows XP system.

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3. Creates the following service:
   
   Service name: WksPatch
   Service binary: %System%\Drivers\Svchost.exe
   Service display name: Constructed in the form of %string1% %string2% %string3%, where:
   
   
   1. %string1% is one of the following:
      
      • Internet
      • License
      • Network
      • Performance
      • Remote
      • Routing
      • Security
      • System
        
        
   2. %string2% is one of the following:
      
      • Accounts
      • Event
      • Logging
      • Manager
      • Procedure
        
        
   3. and %string3% is one of the following:
      
      • Client
      • Messaging
      • Provider
      • Sharing
        
        For example, the service display name can be "Security Logging Sharing."
        
        
4. Deletes the service named "RpcPatch," if it exists.
   
   

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   Note: W32.Welchia.Worm created this service.

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5. Checks for the existence of the W32.Mydoom.A@mm, W32.Mydoom.B@mm, W32.HLLW.Doomjuice, and W32.HLLW.Doomjuice.B worms.
   
   
6. If any of the worms exist, it will attempt to remove them from the system by following these steps:
   
   
   1. Ends the respective processes by name:
      
      
      • %System%\intrenat.exe (W32.HLLW.Doomjuice)
      • %System%\Regedit.exe (W32.HLLW.Doomjuice.B)
      • %System%\Taskmon.exe (W32.Mydoom.A@mm)
      • %System%\Explorer.exe (W32.Mydoom.B@mm)
        
        
   2. Attempts to delete the files associated with the above processes, as well as the following files:
      
      
      • %System%\shimgapi.dll (The .dll associated with W32.Mydoom.A@mm)
      • %System%\ctfmon.dll (The .dll associated with W32.Mydoom.B@mm)
        
        

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        Note: The worm attempts to delete the files before ending the worm processes, so this action will fail.

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   3. Removes the following values from the registry:
      
      
      • HKEY_LOCAL_MACHINE/Software/Microsoft/Windows/CurrentVersion/Run/Gremlin (W32.HLLW.Doomjuice)
      • HKEY_LOCAL_MACHINE/Software/Microsoft/Windows/CurrentVersion/Run/NeroCheck (W32.HLLW.Doomjuice.B)
      • HKEY_LOCAL_MACHINE/Software/Microsoft/Windows/CurrentVersion/Run/Taskmon (W32.Mydoom.A@mm)
      • HKEY_CURRENT_USER/Software/Microsoft/Windows/CurrentVersion/Run/Taskmon (W32.Mydoom.A@mm)
      • HKEY_LOCAL_MACHINE/Software/Microsoft/Windows/CurrentVersion/Run/Explorer (W32.Mydoom.B@mm)
      • HKEY_CURRENT_USER/Software/Microsoft/Windows/CurrentVersion/Run/Explorer (W32.Mydoom.B@mm)
        
        
   4. Restores the following value in the registry (that W32.Mydoom.a@mm and W32.Mydoom.B@mm modify to point to their own DLL):
      
      HKEY_CLASSES_ROOT/CLSID/{E6FB5E20-DE35-11CF-9C87-00AA005127ED}/InProcServer32 = %System\webcheck.dll
      
      
   5. Overwrites the HOSTS file (that Mydoom.A and .B modify) with the following text:
      
      #
      #
      
      127.0.0.1       localhost
      
      
7. Generates random IP addresses, and then sends exploit data to the IP addresses, in an attempt to infect the systems:
   
   • Sends data to TCP port 135 to exploit the DCOM RPC vulnerability.
   • Sends data to TCP port 80 to exploit the WebDav vulnerability.
   • Sends data to TCP port 445 to exploit the Workstation Service vulnerability.
   • Sends data to TCP port 445 to exploit the Locator service vulnerability.
   • Sends data to TCP port 3127 to exploit the Mydoom backdoor.
     
     
8. Runs an HTTP server on a random TCP port, so that the vulnerable computers can reconnect to an infected computer, then locally download and execute the worm as WksPatch.exe.
   
   
9. If the operating system is Japanese, it searches for the files in the IIS Virtual Roots and %Windir%\Help\\IISHelp\common folders if the files have the following extensions:
   
   
   • .shtml
   • .shtm
   • .stm
   • .cgi
   • .php
   • .html
   • .htm
   • .asp
     
     

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     Note: The Virtual Roots and IIS Help folders are installed as part of Microsoft's Internet Information Services server.

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10. May overwrite the files it finds with the following .htm file:
    
    
    
    
    
11. Downloads one of the following patches from Microsoft's Windows Update Web site, if the version of the operating system of the infected computer is Chinese, Korean, or English:
    
    
    • download.microsoft.com/download/4/d/3/4d375d48-04c7-411f-959b-3467c5ef1e9a
      /WindowsXP-KB828035-x86-CHS.exe
    • download.microsoft.com/download/a/4/3/a43ea017-9abd-4d28-a736-2c17dd4d7e59
      /WindowsXP-KB828035-x86-KOR.exe
    • download.microsoft.com/download/e/a/e/eaea4109-0870-4dd3-88e0-a34035dc181a
      /WindowsXP-KB828035-x86-ENU.exe
    • download.microsoft.com/download/9/c/5/9c579720-63e9-478a-bdcb-70087ccad56c
      /Windows2000-KB828749-x86-CHS.exe
    • download.microsoft.com/download/0/8/4/084be8b7-e000-4847-979c-c26de0929513
      /Windows2000-KB828749-x86-KOR.exe
    • download.microsoft.com/download/3/c/6/3c6d56ff-ff8e-4322-84cb-3bf9a915e6d9
      /Windows2000-KB828749-x86-ENU.exe
      
      
12. Installs the patch, and then restarts the computer.
    
    

The worm will self-terminate on July 1, 2004, or after running 140 days, whichever comes first.

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.

Summary