W32.Netspree.Worm

SUMMARY

W32.Netspree.Worm is a worm that spreads over the network shares that are protected with trivial passwords.

W32.Netspree.Worm also uses IRC to notify the remote attackers when it infects a new system. This action may allow a hacker to download programs to the infected computer. The worm may also enable the hacker to use the infected computer as a drone for attacks against other internet-connected computers.

W32.Netspree.Worm does not spread from Windows 95/98/Me systems, although it functions normally in every other way on those platforms.

Protection

• Virus Definitions (LiveUpdate™ Weekly) January 29, 2003
• Virus Definitions (Intelligent Updater) January 23, 2003

Threat Assessment

Wild

• Wild Level: Low
• Number of Infections: 0 - 49
• Number of Sites: 0 - 2
• Geographical Distribution: Low
• Threat Containment: Easy
• Removal: Easy

Damage

• Damage Level: Low

Distribution

• Distribution Level: Low

TECHNICAL DETAILS

The W32.Netspree.Worm consists of these files:

1. Lcp_Netbios.dll
2. Psexec.bat
3. Psexec.exe (A Sysinternals remote execution tool)
4. Psexecsvc.exe (A portion of Psexec.exe)
5. Win32load.exe

The Lcp_Netbios.dll, Psexec.bat, and Win32load.exe files are described in detail below.

Notes:

1. Psexec.exe and Psexecsvc.exe are not malicious, and Symantec antivirus products will not detect them as such. These files will normally be copied to the %System% folder.
   
2. %System% is a variable. The worm locates the System folder and copies the files to that location. By default, this is C:WindowsSystem (Windows 95/98/Me), C:WinntSystem32 (Windows NT/2000), or C:WindowsSystem32 (Windows XP).

• Lcp_Netbios.dll
  
  Lcp_netbios.dll is an NT service that contains the other four files. Lcp_netbios.dll inserts the files on your system, and then executes Psexec.bat.
  
  
• Psexec.bat
  
  Psexec.bat is a simple batch file that takes in, as an argument, the system IP address to be probed.
  
  Psexec.bat consists of approximately 40 lines of this text:
  
  "net use \%1ipc$ <some password> /user:<some user name>"
  
  which probes the IPC$ using trivial user/password combinations (including username/nopassword). Then, it is terminated with a few lines that uses the Psexec.exe file to copy Win32load.exe to the remote system, and then executes it. This will only succeed if an open IPC$ share is found.
  
  The destination folder of the Win32load.exe file is %windir%System32 and is hardcoded into the Psexec.exe utility.
  
  
• WIN32LOAD.EXE
  
  When Win32load.exe is executed, it:
  
  1. Copies itself to the %system% folder, and then executes the copied file.
     
  2. Creates the registry value:
     
     Windows SubSys "<current execution path>WIN32LOAD.EXE" rundll32.dll,loadsubsys,loadsys,win32
     
     under the registry keys:
     
     HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindowsCurrentVersionRun
     HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindowsCurrentVersionRunServices
     
  3. Sets the registry value:
     
     restrictanonymous DWORD:0
     
     under the registry key:
     
     HKEY_LOCAL_MACHINESYSTEMCurrentControlSetControlLsa
     
     Win32load.exe will wait for an active Internet connection. When one is found, it connects to the IRC server master.leet-gamer.net through port 6,667 and joins the channel #lc_breed using a hardcoded password. Then, Win32load.exe will announce its presence divulging information (to anyone who wants to listen) regarding vital information about the infected computer, including the IP address, system type, operating system, cpu type, and so on.
     
     Win32load.exe also contains rudimentary remote control functionality allowing for file downloading and execution. It also allows the computer to be used as a drone in a joint DoS attack against other Internet-connected computers.
     
  4. Downloads and executes Lcp_netbios.dll from a remote Internet site so that the cycle can continue.

Recommendations

Symantec Security Response encourages all users and administrators to adhere to the following basic security "best practices":

• Turn off and remove unneeded services. By default, many operating systems install auxiliary services that are not critical, such as an FTP server, telnet, and a Web server. These services are avenues of attack. If they are removed, blended threats have less avenues of attack and you have fewer services to maintain through patch updates.
• If a blended 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 (for example, all Windows-based computers should have the current Service Pack installed.). Additionally, please apply any security updates that are mentioned in this writeup, in trusted Security Bulletins, or on vendor Web sites.
• 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.
• Configure your email server to block or remove email that contains file attachments that are commonly used to spread viruses, such as .vbs, .bat, .exe, .pif and .scr files.
• Isolate infected computers quickly to prevent further compromising your organization. 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.

REMOVAL

These instructions pertain to all current and recent Symantec antivirus products, including the Symantec AntiVirus and Norton AntiVirus product lines.

1. Update the virus definitions.
2. Do one of the following:
   • Windows 95/98/Me: Restart the computer in Safe mode.
   • Windows NT/2000/XP: End the Trojan process.
3. Run a full system scan and delete all the files detected as W32.Netspree.Worm.
4. Reverse the changes that the Trojan made to the registry.
   

For details on each of these procedures, read the following instructions.

1. Updating the virus definitions
Symantec Security Response fully tests all the virus definitions for quality assurance before they are posted to our servers. There are two ways to obtain the most recent virus definitions:

• Running LiveUpdate, which is the easiest way to obtain the virus definitions. These virus definitions are posted to the LiveUpdate servers once each week (usually on Wednesdays), unless there is a major virus outbreak. To determine whether definitions for this threat are available by LiveUpdate, refer to the Virus Definitions (LiveUpdate), in the "Protection" section, at the top of this writeup.
• Downloading the definitions using the Intelligent Updater. The Intelligent Updater virus definitions are posted on U.S. business days (Monday through Friday). You should download the definitions from the Symantec Security Response Web site and manually install them. To determine whether definitions for this threat are available by the Intelligent Updater, refer to the Virus Definitions (Intelligent Updater), in the "Protection" section, at the top of this writeup.
  
  The Intelligent Updater virus definitions are available here. For detailed instructions on how to download and install the Intelligent Updater virus definitions from the Symantec Security Response Web site, click here.

2. Restarting the computer in Safe mode or ending the Trojan process

• Windows 95/98/Me
  Restart the computer in Safe mode. All the Windows 32-bit operating systems, except for Windows NT, can be restarted in Safe mode. For instructions on how to do this, read the document, "How to start the computer in Safe Mode."
• Windows NT/2000/XP
  To end the Trojan process:
  1. Press Ctrl+Alt+Delete once.
  2. Click Task Manager.
  3. Click the Processes tab.
  4. Double-click the Image Name column header to alphabetically sort the processes.
  5. Scroll through the list and look for Win32load.
  6. If you find the file, click it, and then click End Process.
  7. Exit the Task Manager.
     

3. Scanning for and deleting the infected files

1. Start your Symantec antivirus program and make sure that it is configured to scan all the files.
   • For Norton AntiVirus consumer products: Read the document, "How to configure Norton AntiVirus to scan all files."
   • For Symantec AntiVirus Enterprise products: Read the document, "How to verify that a Symantec Corporate antivirus product is set to scan All Files."
2. Run a full system scan.
3. If any files are detected as infected with W32.Netspree.Worm, click Delete.

4. Reversing the changes made to the registry

CAUTION: Symantec strongly recommends that you back up the registry before you make any changes to it. Incorrect changes to the registry can result in permanent data loss or corrupted files. Modify the specified keys only. Read the document, "How to make a backup of the Windows registry," for instructions.

1. Click Start, and then click Run. (The Run dialog box appears.)
2. Type regedit, and then click OK. (The Registry Editor opens.)
3. Navigate to the key:
   
   HKEY_LOCAL_MACHINESoftwareMicrosoftWindowsCurrentVersionRun
   
4. In the right pane, delete the value:
   
   Windows SubSys
   
5. Navigate to the key:
   
   HKEY_LOCAL_MACHINESoftwareMicrosoftWindowsCurrentVersionRunservices
   
   NOTE: This key will not exist on all systems.
   
6. In the right pane, delete the value:
   
   Windows SubSys
   
7. Navigate to the key:
   
   HKEY_LOCAL_MACHINESYSTEMCurrentControlSetControlLsa
   
8. In the right pane, double-click:
   
   restrictanonymous
   
9. Change the value to:
   
   DWORD:1
   
10. Exit the Registry Editor.