W32.Randex.E

1. Copies itself as one of the following:
   
   %System%\nstask32.exe
   %System%\winlogin.exe
   
   
2. Copies itself to the Windows Temp folder using some randomly generated file names.
   
   
3. Creates one of the following:
   
   %System%\win32sockdrv.dll
   %System%\yuetyutr.dll
   
   The worm injects the dropped DLL as a module into the Explorer.exe process. It also uses the dropped DLL file to spread itself through IRC, and uses the DLL to exploit the DCOM RPC vulnerability, as described in Microsoft Security Bulletin MS03-026.
   
   
4. Adds the value:
   
   "NDplDeamon"="nstask32.exe"
   
   or:
   
   "NDpLDeamon"="winlogin.exe"
   
   to the registry keys:
   
   HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Runonce
   HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Run
   
   
5. One variant also adds a value:
   
   "winlogon"="winlogin.exe"
   
   to the registry key:
   
   HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Run
   
   
6. Inserts the following lines to the System.ini file, if the system is Windows 95, 98, or Me:
   
   [boot]
   shell = explorer.exe  <the worm file, for example, nstask32.exe>
   
   
7. In Windows NT/2000/XP, it modifies the "Shell"= value of the registry key:
   
   HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon
   
   to one of the following:
   
   "Shell"="explorer.exe winlogin.exe"
   
   or:
   
   "Shell"="explorer.exe nstask32.exe"
   
   
8. The worm contains its own IRC client, allowing it to connect to specified IRC servers and join a channel to listen for commands from the worm's creator.
   
   One such command is to exploit the DCOM RPC vulnerability: The worm generates random IP addresses. Once the IP address is generated, it sends specially formed data, which exploits the DCOM RPC vulnerability, to that particular IP address.
   
   
9. Creates a hidden Cmd.exe remote shell that will listen on TCP port 4444, allowing an attacker to issue remote commands on an infected system.
   
   
10. Creates a thread running as a TFTP server, listening on UDP port 69. When the worm receives a request from a computer to which it can connect using the DCOM RPC exploit, it will send Nstask32.exe or Winlogin.exe to that particular computer and tell it to execute the worm.

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.