W32.HLLW.Shorm.B

SUMMARY

W32.HLLW.Shorm.B is a 32-bit worm that spreads by attempting to connect to a predetermined set of IP addresses. It contains a password stealer, and updates itself from a Web site in Russia. The worm emails passwords to the hacker using an anonymous mail host in Russia.

Protection

• Virus Definitions (LiveUpdate™ Weekly) October 9, 2002
• Virus Definitions (Intelligent Updater) October 8, 2002

Threat Assessment

Wild

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

Damage

• Damage Level: Low
• Modifies Files: Modifies the registry
• Releases Confidential Info: Password stealer

Distribution

• Distribution Level: Medium
• Target of Infection: Tries to connect to a specified set of IP addresses via open shares.

TECHNICAL DETAILS

W32.HLLW.Shorm.B is a variant of W32.HLLW.Shorm. Because it updates itself when it runs, the names of the files that it drops are not constant.

When the worm starts, it checks a Web site in Russia for updated versions, which are usually named Wormxx.bmp, where xx is a two-digit value. The worm downloads the new file and runs it. When the file runs, the worm moves itself to the %windir% folder. Known file names to which the worm moves itself are:

• Interet32.exe
• Winint32.exe
  
  NOTE: If the dropped file is Winint32.exe, the worm also drops %windir%Mpr32.dll.
  
• Files32.vxd

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

The worm also changes registry settings.

• If the dropped file is %windir%Interet32.exe
  
  it adds the value
  
  Interet32 Interet32.exe
  
  to the registry key
  
  HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindowsCurrentVersionRun
  
• If the dropped file is %windir%Winint32.exe
  
  it adds the value
  
  Winint32 Winint32.exe
  
  to the registry key
  
  HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindowsCurrentVersionRun
  
• If the dropped file is %windir%Files32.vxd, it changes the (Default) value of
  
  HKEY_LOCAL_MACHINESoftwareClassesexefileshellopencommand
  
  to
  
  Files32.vxd "%1%*
  
  This causes the worm to run whenever an .exe file runs.

The worm also downloads a file containing the first three octets of an IP address range. It then tries to connect to the addresses by filling in the last octet. It tests for shares and attempts to copy itself into the Windows startup folder. It copies itself as one of the following:

• Auto.exe
• Auto16.exe
• Worm23.exe
• Worm25.exe
• Script.exe

By placing itself into this folder, the worm runs each time that you start Windows.

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

NOTES:

• These instructions are for all current and recent Symantec antivirus products, including the Symantec AntiVirus and Norton AntiVirus product lines.
• If the variant that drops the Files32.vxd has run, you will not be able to start most programs, including Symantec antivirus software or LiveUpdate. In this case, first follow the instructions in the section To edit the registry so that you can run .exe files, which follows.

1. Update the virus definitions.
2. Run a full system scan, and delete all files that are detected as W32.HLLW.Shorm.B.
3. Delete either of these values:
   
   Interet32     Interet32.exe
   
   Winint32      Winint32.exe
   
   from the registry key
   
   HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindowsCurrentVersionRun
   

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

To update the virus definitions:
All virus definitions receive full quality assurance testing by Symantec Security Response before being posted to our servers. There are two ways to obtain the most recent virus definitions:

• Run LiveUpdate, which is the easiest way to obtain virus definitions. These virus definitions 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 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.

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 with W32.HLLW.Shorm.B, click Delete.

To delete the value that the worm added 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 either of these values:
   
   Interet32 Interet32.exe
   
   Winint32 Winint32.exe
   
5. Exit the Registry Editor.

To edit the registry so that you can run .exe files:
This is necessary only if you cannot run most programs. 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.

To copy the Registry Editor:

1. Do one of the following, depending on which version of Windows you are running:
   • Windows 95/98 users: Click Start, point to Programs, and click MS-DOS Prompt. A DOS window opens at the C:Windows prompt. Proceed to step 2 of this section.
   • Windows Me users: Click Start, point to Programs, point to Accessories, and then click MS-DOS Prompt. A DOS window opens at the C:Windows prompt. Proceed 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. Proceed 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, as well.
   

1. Proceed to the next section.

NOTE: 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, as well.

To edit 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. Navigate to and select the following key:
   
   HKEY_LOCAL_MACHINESoftwareClassesexefileshellopencommand
   
   CAUTION: The HKEY_LOCAL_MACHINESoftwareClasses 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_LOCAL_MACHINESoftwareClassesexefileshellopencommand subkey that is shown in the following figure:
   
   <<=== NOTE: Modify this key.
   
2. In the right pane, double-click the (Default) value.
3. Delete the current value data, and then type: "%1" %* (That is, type the following characters: quote-percent-one-quote-space-percent-asterisk.)
   
   NOTES:
   • Under Windows 95/98/Me/NT, the Registry Editor automatically encloses the value within quotation marks. When you click OK, the (Default) value should look exactly like this:
     
     ""%1" %*"  
     
   • Under Windows 2000/XP, 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.
     
4. Exit the Windows registry.
5. Go back to the beginning of these removal instructions, starting with To update the virus definitions.