W32.Dalbug.Worm

When breaking into a remote computer, W32.Dalbug.Worm attempts to open the computer's Service Control Manager. If successful, it will install itself on the remote computer as a service. The service will have the following attributes:

• Service name: NtLmHosts
• Display name: TCP/IP NetBIOS Provider
• Description: Provides NetBIOS over TCP/IP (NetBT) service support for NetBIOS name resolution.
• Path: %windir%\System32\lmhsvc.exe

W32.Dalbug.Worm then copies itself as %windir%\System32\lmhsvc.exe, so that the worm is run each time that you restart the computer.

Once it is running, W32.Dalbug.Worm inserts and executes these files:

• %windir%\Smss.exe
• %windir%\Csrss.exe

NOTE: %windir% is a variable. It is the folder where Windows is installed. By default, this is C:\Winnt on Windows NT/2000 systems or C:\Windows on Windows XP systems.

It also inserts the file %windir%\System32\Lady.exe. This is a non-malicious joke program that is executed by Smss.exe and Csrss.exe once they are running.

NOTE: The files Smss.exe and Csrss.exe have the same file names as two system files that reside in the %windir%\System32 folder. If you delete these files manually, make sure that you delete the copies that are in the home folder and not the ones in the System32 folder.

During execution, the Smss.exe and Csrss.exe files keep the service running, and checking every three seconds to make sure that it is still running. If you attempt to change or disable the service, it will immediately reinstall it. After 5 minutes of execution time, they activate the Lady.exe program , which will display a few flies crawling across the screen.

During its execution W32.Dalbug.Worm will periodically (every 10 seconds) also add the following registry values:

Smss.exe       %windir%\smss.exe
Csrss.exe      %windir%\csrss.exe

to the registry key

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run

In addition, it tries to kill the Regedit.exe process if it is activated.

Smss.exe and Csrss.exe also try to create the these registry values, however if they detect that Regedit.exe is running, they will delete them (instead of creating them).

Finally, Smss.exe and Csrss.exe will also copy the worm to the following files:

%windir%\inf\Cdrom.sys
%windir%\Fonts\Dosoem.fon
%windir%\Help\Dosapp.hlp

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