W32.HLLW.Kilonce

SUMMARY

W32.HLLW.Kilonce is a worm that spreads through open shares. It is based on the W32.Nimda worm but without the e-mailing capabilities. It attempts to kill any processes which contain the characters "KV" or "AV" or that is named "Load.exe" and subsequently delete the associated file.

Behavior

Symptoms

Transmission

Protection

• Virus Definitions (LiveUpdate™ Weekly) August 28, 2002
• Virus Definitions (Intelligent Updater) August 28, 2002

Threat Assessment

Wild

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

Damage

• Damage Level: High
• Payload Trigger: 13th December in any year
• Deletes Files: All deletable files and subdirectories on the C: drive will be deleted when the payload activates.
• Compromises Security Settings: Guests might be granted Administrator access; unrestricted shares might be created for drives C: - K:

Distribution

• Distribution Level: Low
• Shared Drives: Copies itself as Rundll32.exe or Regedit.exe across shared drives.

TECHNICAL DETAILS

When the worm is first run, it checks the name of the current computer. If the name is not "YWB" then the worm performs the following actions:

It creates a thread that will enumerate all processes and kill any process whose name contains "KV" or "AV" or is named "LOAD.EXE." After the process is killed, the associated file will be deleted.

It copies itself as

• C:\%windir%Killonce.exe
• C:RecycledKillonce.exe

NOTE: %windir% is a variable. The worm locates the Windows installation folder (by default this is C:Windows or C:Winnt) and copies itself to that location.

Next, it alters several registry keys:

• In the key
  
  HKEY_CLASSES_ROOTexefileshellopencommand
  
  it changes the Value Data of (Default) to
  
  %windir%killonce.exe "%1 %*
  
  
• In the key
  
  HKEY_CLASSES_ROOT xtfileshellopencommand
  
  it changes the Value Data of (Default) to
  
  c:ecycledkillonce.exe %windir%NotePad %1
  
  The original contents of this value are lost.
  
• In the key
  
  HKEY_LOCAL_MACHINESoftwareMicrosoftWindowsCurrentVersionRun
  
  it adds the value
  
  KillOnce %windir%killonce.exe
  
  This will cause the worm to run each time that you start Windows.
  

It adds the Guest account to the Administrators group under Windows NT/2000/XP.

It opens all hard drives from C to K for unrestricted sharing under Windows 95/98/Me.

The worm will then enumerate network resources. If it finds the file Rundll32.exe in the Windows folder on the remote computer, then the worm renames it to Run32.exe and replaces the original file with a copy of the worm. If it finds Regedit.exe on the remote computer, then the worm renames it to Regedit.exe.sys and replaces the original file with a copy of the worm.

The worm overwrites any file whose file extension is .eml or .nws. The overwritten file will contain a base64-encoded version of the worm.

If the worm finds any file whose extension is .doc, then the worm will copy itself as Riched20.dll.

If the worm finds any file whose extension is .htm, then the worm will copy itself as Shdocvw.dll.

On the 13th of December in any year, the worm will overwrite the Autoexec.bat with code to delete all files and subfolders in the C drive.

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

NOTE: These instructions are for all current and recent Symantec antivirus products, including the Symantec AntiVirus and Norton AntiVirus product lines.

1. Update the virus definitions, and then restart the computer in Safe mode.
2. Copy Regedit.exe to Regedit.com.
3. Using Regedit.com, reverse the changes that were made to the registry.
   
   CAUTION: If doing this on a remote computer that was infected across the network by another infected computer, you must first rename Regedit.exe.sys back to Regedit.exe.
   
4. Run a full system scan, and delete all files that are detected as W32.HLLW.Kilonce. Restore any needed overwritten files from a clean backup.
   

For details on how to do this, read the following instructions.


To update the virus definitions and restart in Safe mode:

1. Obtain the most recent virus definitions. There are two ways to do this:
   • Run LiveUpdate, which is the easiest way to obtain virus definitions. These virus definitions have undergone full quality assurance testing by Symantec Security Response and are posted to the LiveUpdate servers one time each week (usually Wednesdays) unless there is a major virus outbreak. To determine whether definitions for this threat are available by LiveUpdate, look at the Virus Definitions (LiveUpdate) line at the top of this write-up.
   • Download the definitions using the Intelligent Updater. Intelligent Updater virus definitions have undergone full quality assurance testing by Symantec Security Response. They are posted on U.S. business days (Monday through Friday). They must be downloaded from the Symantec Security Response Web site and installed manually. To determine whether definitions for this threat are available by the Intelligent Updater, look at the Virus Definitions (Intelligent Updater) line at the top of this write-up.
     
     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. Restart the computer in Safe mode. All Windows 32-bit operating systems, except 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.

To copy Regedit.exe to Regedit.com:
Because the worm modified the registry so that you cannot run .exe files, you must first make a copy of the Registry Editor as a file with the .com extension, and then run that file.

CAUTION: If doing this on a remote computer that was infected across the network by another infected computer, you must first rename Regedit.exe.sys back to Regedit.exe.

1. Do one of the following, depending on which operating system you are running:
   • Windows 95/98 users: Click Start, point to Programs, and click MS-DOS Prompt. This opens a DOS window at the C:Windows prompt. Go on to step 2 of this section.
   • Windows Me users: Click Start, point to Programs, point to Accessories, and then click MS-DOS Prompt. This opens a DOS window at the C:Windows prompt. Go on to step 2 of this section.
   • Windows NT/2000 users:
     1. Click Start, and click Run.
     2. Type the following and then press Enter:
        
        command
        
        A DOS window opens.
        
     3. Type the following and then press Enter:
        
        cd winnt
        
     4. Go on to step 2 of this section.
   • Windows XP:
     1. Click Start, and click Run.
     2. Type the following and then press Enter:
        
        command
        
        A DOS window opens.
        
     3. Type the following and then press Enter after typing each one:
        
        cd
        cd windows
        
     4. Proceed to step 2 of this section.
        
2. Type the following and then press Enter:
   
   copy regedit.exe regedit.com
   
3. Type the following and then press Enter:
   
   start regedit.com
   
   The Registry Editor will open in front of the DOS window. After you finish editing the registry, exit the Registry Editor, and then exit the DOS window.
   

1. Proceed to the next section, "To edit the registry and remove keys and changes made by the worm," only after you have accomplished the previous steps.


NOTES:

• The Registry Editor will open in front of the DOS window. After you finish editing the registry and have closed the Registry Editor, then close the DOS window.
• After W32.HLLW.Kilonce has been successfully removed, then you may delete the Regedit.com file.

To reverse the changes that were 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 only the keys that are specified. Read the document How to make a backup of the Windows registry for instructions.

1. Click Start, and 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
   
   KillOnce %windir%killonce.exe
   
5. Navigate to and select the following key:
   
   HKEY_CLASSES_ROOTexefileshellopencommand
   
   CAUTION: The HKEY_CLASSES_ROOT key contains many subkey entries that refer to other file extensions. One of these file extensions is .exe. Changing this extension can prevent any files ending with an .exe extension from running. Make sure that you browse all the way along this path until you reach the command subkey.
   
   Modify the HKEY_CLASSES_ROOTexefileshellopencommand subkey that is shown in the following figure:
   
   <<=== NOTE: Modify this key.
   
6. In the right pane, double-click the (Default) value.
7. Delete the current value data, and then type: "%1" %* (That is, type the following characters: quote-percent-one-quote-space-percent-asterisk.)
   
   NOTES:
   • On Windows 95/98/Me and Windows NT systems, the Registry Editor automatically encloses the value within quotation marks. When you click OK, the (Default) value should look exactly like this:
     
     ""%1" %*"  
     
   • On Windows 2000/XP systems, the additional quotation marks will not appear. When you click OK, the (Default) value should look exactly like this:
     
     "%1" %*
     
   • Make sure that you completely delete all value data in the command key before you type the correct data. If you leave a space at the beginning of the entry, any attempt to run program files will result in the error message, "Windows cannot find .exe." If this happens to you, start over at the beginning of this document, and make sure that you completely remove the current value data.
     
8. Navigate to and select the following key:
   
   HKEY_CLASSES_ROOT xtfileshellopencommand
   
9. In the right pane, double-click the (Default) value.
10. Delete the current value data and replace it with the correct text for your version of Windows and installation. This value will vary, however. For example, on a standard Windows 2000 installation, it may be:
    
    %SystemRoot%system32NOTEPAD.EXE %1
    
    We suggest that you either look at the same value on a uninfected computer that has the same Operating System and configuration or consult a qualified computer technician.
    
11. Exit the Registry Editor.

To scan for and delete the infected files:

1. Start your Symantec antivirus program, and make sure that it is configured to scan all files.
   • Norton AntiVirus consumer products: Read the document How to configure Norton AntiVirus to scan all files.
   • Symantec enterprise antivirus products: Read the document How to verify 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 by W32.HLLW.Kilonce, click Delete.
4. Restart the computer to normal mode. Restore any needed overwritten files from a clean backup.