Threat Explorer

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VBS.Saur.A

VBS.Saur.A

Updated:
13 February 2007
Also Known As:
Bulbasaur

This worm is written in Visual Basic Script and is spread via Microsoft Outlook. The worm mails itself to everyone in the Outlook address book. It arrives in email as a Batch file (bulbasaur.bat) and creates a VBS and HTML file for further propagation. The worm also attempts to spread itself by IRC via mIRC or Pirch, sending the HTML version of itself to other users via DCC.

Since the virus utilizes Visual Basic Script, you need Windows Scripting Host installed, which is the default under Windows 98 and Windows 2000. Windows Scripting Host is also installed with the latest version of Internet Explorer.

Antivirus Protection Dates

  • Initial Rapid Release version 25 July 2000
  • Latest Rapid Release version 31 May 2016 revision 036
  • Initial Daily Certified version 25 July 2000
  • Latest Daily Certified version 01 June 2016 revision 005
  • Initial Weekly Certified release date pending
Click here for a more detailed description of Rapid Release and Daily Certified virus definitions.

When the batch file is executed, the worm copies itself to <Windows>\bulbasaur.bat. Then, the worm creates and executes <Windows>\Bulbasaur.vbs using a temporary file calld BulBasaur1.vbs. The worm finally displays the following message and then exits:
    Fatal ERROR. Can't Run the application.
When BulBasaur.vbs is executed, it copies <Windows>\Bulbasaur.vbs to \Bulbasaur.bat. It then creates the following registry key:
HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Run\BulbaSaur = \wscript.exe BulbaSaur.vbs %

Finally, the email replication routine begins. The worm verifies that the email replication routine has been run by checking for the presence of the following registry key:
HKCU\Software\BulBasaur\Mailme

If the routine has not yet run, the worm emails everyone in the Microsoft Outlook address book. The email will have the subject:
    Rv: New Stuff 4You
and the body:

    Check this new funny game!

    It's just great!
with the bulbasaur.bat file attached.

The worm then creates the HKCU\Software\BulBasaur\Mailme registry key.

In addition to email, the worm can spread via mIRC or Pirch. The worm creates the file \bulbsaur.html and searches all drives for the presence of mIRC or Pirch by searching for the files mirc.ini or events.ini respectively. The files will be replaced with viral code, allowing the virus to transmit itself to other IRC users via DCC. If both mIRC and Pirch are present, only one will be infected.

When opening the HTML file with the default installation of Internet Explorer, you will receive a Microsoft ActiveX warning dialog box. If you click No, the worm will be unable to run. The worm will then display:
    You need ActiveX enabled to see this file
    Click Here to reload and click Yes

If you click Yes, the worm will display:
    This document has permanent errors, try downloading it again

The HTML file will create the original Batch file that is received by email in the Windows directory and execute it. If any of the files created by the worm are deleted and the worm is run, it will attempt to replace the deleted files.

Recommendations

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

  • Use a firewall to block all incoming connections from the Internet to services that should not be publicly available. By default, you should deny all incoming connections and only allow services you explicitly want to offer to the outside world.
  • 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.
  • Ensure that programs and users of the computer use the lowest level of privileges necessary to complete a task. When prompted for a root or UAC password, ensure that the program asking for administration-level access is a legitimate application.
  • Disable AutoPlay to prevent the automatic launching of executable files on network and removable drives, and disconnect the drives when not required. If write access is not required, enable read-only mode if the option is available.
  • Turn off file sharing if not needed. If file sharing is required, use ACLs and password protection to limit access. Disable anonymous access to shared folders. Grant access only to user accounts with strong passwords to folders that must be shared.
  • Turn off and remove unnecessary services. By default, many operating systems install auxiliary services that are not critical. These services are avenues of attack. If they are removed, threats have less avenues of attack.
  • If a 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.
  • Configure your email server to block or remove email that contains file attachments that are commonly used to spread threats, such as .vbs, .bat, .exe, .pif and .scr files.
  • Isolate compromised computers quickly to prevent threats from spreading further. 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.
  • If Bluetooth is not required for mobile devices, it should be turned off. If you require its use, ensure that the device's visibility is set to "Hidden" so that it cannot be scanned by other Bluetooth devices. If device pairing must be used, ensure that all devices are set to "Unauthorized", requiring authorization for each connection request. Do not accept applications that are unsigned or sent from unknown sources.
  • For further information on the terms used in this document, please refer to the Security Response glossary.

To remove this virus:
  1. Remove the following registry keys:
    HKCU\Software\BulBasaur\Mailme
    HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Run\BulbaSaur

  2. Delete all detected files, including the following:
    • <Windows>\bulbasaur.bat
    • BulBasaur1.vbs
    • \Bulbasaur.bat
    • <Windows>\Bulbasaur.vbs
    • <Windows>\bulbsaur.html
    • \Script.ini
    • \events.ini
Writeup By: Eric Chien