W32.BlueCode.Worm

The worm infects computers running Windows NT and 2000 by using the Unicode Web Traversal IIS exploit. Information about this exploit is available at http://www.microsoft.com/technet/security/bulletin/ms00-078.asp.

Using the exploit, the worm does the following:

1. It executes FTP on the victim server to retrieve the file Httpext.dll from the attacking server. Httpext.dll is placed in an executable directory (such as C:\Inetpub\wwwroot\scripts) on the victim server.
2. Next, the worm executes Httpext.dll on the victim server by making an HTTP GET call to the malicious .dll.
   
   NOTE: Httpext.dll is an ISAPI .dll. To execute it, the worm accessed it as a URL (for example, http:/ /domain.tld/scripts/httpext.dll).
   
3. The .dll creates a mutex named "CodeBlue" so that it will execute only once. Then, the .dll creates the C:\Svchost.exe file and executes it.
4. Svchost.exe performs the infection and denial-of-service routines:
   1. First, the value
      
      Domain Manager C:\svchost.exe
      
      is added to the registry key
      
      HKEY_LOCAL_MACHINE\Software\Microsoft\
      Windows\CurrentVersion\Run
      
      which allows the worm to execute after a restart.
   2. Next, the worm drops a temporary file, C:\d.vbs. This file is a Visual Basic Scripting file and is executed by the virus by calling C:\WINNT\system32\Wscript.exe.
   3. The VBS file removes the .ida, .idq, and .printer IIS service mappings preventing other exploits such as Code Red. The worm later deletes this file.
   4. Next, the worm generates random IP addresses, and the infection routine begins again.
   5. If the time is between 10 A.M. and 11 A.M., the worm attempts a denial-of service-attack by sending a large amount of data to an Internet security company's Web site, which is located in China.
   6. Finally, multiple threads are created which can cause system instability and force the system to be inoperable.

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