W32.Estrella

SUMMARY

W32.Estrella is a Trojan horse that is designed to be spread through floppy disks. This trojan deletes some specific files on December 15th. It is written in Microsoft Visual Basic programming language.

NOTE: Virus definitions dated prior to June 13, 2002 may detect this threat as Backdoor.Trojan.

Protection

• Virus Definitions (LiveUpdate™ Weekly) June 19, 2002
• Virus Definitions (Intelligent Updater) June 14, 2002

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
• Payload Trigger: Dec. 15th
• Payload: Deletes files.
• Deletes Files: Various files on drive C and all files/folders on drive D.

Distribution

• Distribution Level: Low
• Target of Infection: drive A:

TECHNICAL DETAILS

As part of its routine, W32.Estrella creates a copy of itself on a floppy disk as A:Estrella.exe. This is how it is designed to spread. It has the standard Windows folder icon to deceive you.

If A:Estrella.exe (the Trojan) is then executed, it does the following:

It adds the following values:

Win32G      C:\%System%Kernel32.com
Win32R      C:\%Windows%Server.com

to the registry key:

HKEY_LOCAL_MACHINESoftwareMicrosoftWindowsCurrentVersionRun

It adds the value:

Win32G       C:\%Windows%COMMANDScandisk.com

to the registry key:

HKEY_CURRENT_USERSoftwareMicrosoftWindowsCurrentVersionRun

As a result of the three registry value additions, the Trojan runs when you start Windows.

Next, it copies itself as:

• C:\%Windows%Server.com
• C:\%System%Kernel32.com
• C:\%Windows%COMMANDScandisk.com

NOTES:

• %Windows% is a variable. The worm locates the Windows folder (by default this is C:Windows or C:Winnt) and copies itself to that location
• %System% is a variable. The worm locates the WindowsSystem folder (by default this is C:WindowsSystem or C:WinntSystem32) and copies itself to that location
• If the executed Trojan file name is not Estrella.exe, Server.com, Kernel32.com, or Scandisk.com, it does not copy itself to any files; it only adds the values to the registry.

If the date is December 15th, the Trojan does the following:

• It displays the message:
  
  
  
• It deletes the following files if they are found:
  • C:Command.com
  • C:Config.sys
  • C:Autoexec.bat
  • C:WindowsCommandFormat.com
  • C:WindowsOptionsInstallFormat.com
  • C:WindowsCommand.com
  • C:Mis Documentos*.doc
  • C:BorlandcBin*.cpp
  • C:BorlandcBin*.c
  • C:BorlandcBgi*.cpp
  • C:BorlandcBgi*.c
  • C:Archivos De ProgramaMicrosoft Visual StudioVb98*.frm
  • C:Archivos De ProgramaMicrosoft Visual StudioVb98Bin*.cpp
  • C:*.doc
• It removes all folders and files on drive D.

Every few hours, it searches drive A for the file Estrella.exe. If a floppy disk is in drive A, and Estrella.exe is not found, it copies itself to the floppy as Estrella.exe.

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

To remove this Trojan:

1. Update the virus definitions, run a full system scan, and delete all files that are detected as W32.Estrella.
2. Delete the values that it added to the registry keys:
   
   HKEY_LOCAL_MACHINESoftwareMicrosoftWindowsCurrentVersionRun
   HKEY_CURRENT_USERSoftwareMicrosoftWindowsCurrentVersionRun

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

To scan with Norton AntiVirus and delete the infected files:

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. Start Norton AntiVirus (NAV), and make sure that NAV is configured to scan all files.
   • NAV Consumer products: Read the document How to configure Norton AntiVirus to scan all files.
   • NAV Enterprise products: Read the document How to verify a Symantec Corporate antivirus product is set to scan All Files.
3. Run a full system scan.
4. Delete all files that NAV detects as W32.Estrella. Files that were deleted by the Trojan should be replaced from backup or reinstalled.

To remove the value from 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 following key:
   
   HKEY_LOCAL_MACHINESoftwareMicrosoftWindowsCurrentVersionRun
   
4. In the right pane, delete the following value:
   
   Win32G      C:\%System%Kernel32.com
   Win32R      C:\%Windows%Server.com
   
5. Navigate to the following key:
   
   HKEY_CURRENT_USERSoftwareMicrosoftWindowsCurrentVersionRun
   
6. In the right pane, delete the following value:
   
   Win32G       C:\%Windows%COMMANDScandisk.com
   
7. Click Registry, and click Exit.