VBS.Confi

SUMMARY

VBS.Confi is a Visual Basic Script (VBScript) virus that spreads through floppy disks. When it is executed, it launches a "windowbomb" by repeatedly opening Web browser windows. The 11th time that this virus is executed, it replaces the "Winstart.bat" file with commands to delete all the files on the A, C, D, and E drives.

This virus consists of a VBScript embedded in a .htt (hypertext template) file. Windows normally uses the .htt files to control how folders are displayed in Windows Explorer. VBS.Confi uses this mechanism to ensure that the virus is executed every time a folder is opened. It is possible to infect a computer with VBS.Confi, by viewing the contents of an infected floppy disk with Windows Explorer.

The presence of the file MSkernel32.con or MSkernel.con is a sign of possible infection.

Virus definitions dated prior to October 24, 2003 may detect this threat as JS.Exception.Exploit.

Protection

• Virus Definitions (LiveUpdate™ Weekly) October 29, 2003
• Virus Definitions (Intelligent Updater) October 24, 2003

TECHNICAL DETAILS

When VBS.Confi is executed, it:

1. Modifies various registry settings to disrupt the normal system operation:
   
   
   • Sets the value:
     
     "Hidden"=0
     
     in the registry key:
     
     HKEY_USERS.DEFAULTSoftwareMicrosoftWindowsCurrentVersionExplorerAdvanced
     
     
   • Sets the values:
     
     "NoFolderOptions"=1
     "NoCustomizeWebView"=1
     
     in the registry key:
     
     HKEY_USERS.DEFAULTSoftwareMicrosoftWindowsCurrentVersionPoliciesExplorer
     
     
   • Sets the value:
     
     "DisableRegistryTools"=1
     
     in the registry key:
     
     HKEY_USERS.DEFAULTSoftwareMicrosoftWindowsCurrentVersionPoliciesSystem
     
     
   • Sets the values:
     
     "NoRealMode"=1
     "Disabled"=1
     
     in the registry key:
     
     HKEY_USERS.DEFAULTSoftwareMicrosoftWindowsCurrentVersionPoliciesWinOldApp
     
     
2. Copies itself as:
   
   • %Windir%SystemMSkernel32.con
   • %Windir%SystemMSkernel.con
     
     if it is run from a floppy disk, or as:
     
     
   • A:folder.htt
   • A:desktop.ini
     
     if it is run from the %Windir%System directory.
     
     

     ---

     Note: %Windir% is a variable. The virus locates the Windows installation folder (by default, this is C:Windows or C:Winnt) and copies itself to the System subdirectory.

     ---

     
     
3. Sets the ".con" extension to be synonymous with the ".htt" (hypertext template) extension by creating the following registry keys:
   
   HKEY_CLASSES_ROOT.con
   HKEY_CLASSES_ROOTconfile
   
   
4. Sets itself to be the default template used to view folders with Windows Explorer, by setting the value:
   
   "PersistMoniker"="file:/ /%Windir%systemMSkernel32.con"
   
   in the registry key:
   
   HKEY_CLASSES_ROOTDirectoryshellexExtShellFolderViews{5984FFE0-28D4-11CF-AE66-08002B2E1262}
   
   
5. Repeatedly pops up Internet Explorer windows. This will likely cause the system to become unresponsive, requiring a restart.
   
   
6. Increments a counter, stored in the registry as:
   
   HKEY_LOCAL_MACHINESoftwareMicrosoftMediaPlayerSetupMeta Status.
   
   The 11th time the virus is executed, it creates or overwrites %Windir%Winstart.bat with commands to run deltree on the A:, C:, D:, and E: drives. On Windows 95/98 systems, the commands will be executed the next time Windows is rebooted.
   
   The malicious Winstart.bat file is detected as BAT.Trojan.
   

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

What you need to do depends on whether the Trojan has actually executed.

If VBS.Confi has already executed
If VBS.Confi has run 10 or fewer times, it has made numerous system modifications that make manual repair difficult. The easiest method to fix it is to restore the entire registry from a backup copy. Read your Windows or backup software documentation for more information.

If VBS.Confi has executed 11 times, and the system was subsequently restarted, it may have deleted the files. In this case, it is possible that you will no longer be able to start Windows, and it will be necessary to either restore system files from a backup copy, or to re-install the operating system.

Once you have replaced the registry with a clean copy and restored any missing system files, update the virus definitions and run a full system scan as described in the next section.


If VBS.Confi has not yet executed
If your Symantec antivirus product detects VBS.Confi, delete it. If you suspect that the virus exists on your system, but has not yet executed, follow these steps:

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

1. Disable System Restore (Windows Me/XP).
2. Update the virus definitions.
3. Run a full system scan and delete all the files detected as VBS.Confi or BAT.Trojan.

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

1. Disabling System Restore (Windows Me/XP)
If you are running Windows Me or Windows XP, we recommend that you temporarily turn off System Restore. Windows Me/XP uses this feature, which is enabled by default, to restore the files on your computer in case they become damaged. If a virus, worm, or Trojan infects a computer, System Restore may back up the virus, worm, or Trojan on the computer.

Windows prevents outside programs, including antivirus programs, from modifying System Restore. Therefore, antivirus programs or tools cannot remove threats in the System Restore folder. As a result, System Restore has the potential of restoring an infected file on your computer, even after you have cleaned the infected files from all the other locations.

Also, a virus scan may detect a threat in the System Restore folder even though you have removed the threat.

For instructions on how to turn off System Restore, read your Windows documentation, or one of the following articles:

• "How to disable or enable Windows Me System Restore"
• "How to turn off or turn on Windows XP System Restore"

For additional information, and an alternative to disabling Windows Me System Restore, see the Microsoft Knowledge Base article, "Antivirus Tools Cannot Clean Infected Files in the _Restore Folder," Article ID: Q263455.

2. 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 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).
• 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).
  
  The Intelligent Updater virus definitions are available: Read "How to update virus definition files using the Intelligent Updater" for detailed instructions.

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 VBS.Confi or BAT.Trojan, note the path and file name, and then click Delete.
4. Manually delete other files that the Trojan uses. (These files are not harmful by themselves, and therefore, Symantec antivirus products do not detect them.)
   • If VBS.Confi was detected on a floppy disk (for example, A:folder.htt), delete the corresponding desktop.ini file (A:desktop.ini).
   • If VBS.Confi was detected as a file named MSKernel32.con, delete MSKernel.con from the same directory.