Threat Explorer

The Threat Explorer is a comprehensive resource consumers can turn to for daily, accurate, up-to-date information on the latest threats, risks and vulnerabilities.

VBS.Kasnar

VBS.Kasnar

Discovered:
13 March 2003
Updated:
13 February 2007
Systems Affected:
Windows

VBS.Kasnar is a Trojan horse that creates many garbage text files on the infected computer.

Antivirus Protection Dates

  • Initial Rapid Release version 14 March 2003
  • Latest Rapid Release version 28 September 2010 revision 054
  • Initial Daily Certified version 14 March 2003
  • Latest Daily Certified version 28 September 2010 revision 036
  • Initial Weekly Certified release date 19 March 2003
Click here for a more detailed description of Rapid Release and Daily Certified virus definitions.

When VBS.Kasnar runs, it does the following:
  1. Copies itself as %Windir%\sysops.vbs.

    NOTE: %Windir% is a variable. The Trojan locates the Windows installation folder (by default, this is C:\Windows or C:\Winnt) and copies itself to that location.
  2. Adds the value

    MSrundll32 sysops.vbs

    to the registry key

    HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run

    so that the Trojan runs when you start Windows.
  3. Modifies the value data of the value RegisteredOwner in the registry key

    HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion

    to

    RegisteredOwner DumbaSS
  4. If the current system day is 7, the Trojan displays three messages with the following characteristics:

    Text: This virus is dedicated to the Black Cat Virus Group, you guys rule!
    Text: VBS.Ransak by wHacker...pure annoyance
    Text: Currently spawning 100,000 files in multiple folders and drives, good day!

    The Trojan then creates many 116-byte text files in the following folders:

    C:\
    C:\Windows
    C:\Windows\System32
    C:\Program Files\KaZaA\KaZaA Lite\my shared folder
    A:\

    The files have numbers as the names and .txt as extension. For example, the file may be named 78.txt. Those files are not viral by themselves; therefore, Symantec antivirus products do not detect them. You should delete them manually if the computer is infected with the Trojan.

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.

The following instructions pertain to all current and recent Symantec antivirus products, including the Symantec AntiVirus and Norton AntiVirus product lines.
  1. Update the virus definitions.
  2. Run a full system scan, and delete all the files that are detected as VBS.Kasnar.
  3. Manually delete all text files created by the Trojan.
  4. Delete the values that the Trojan added to the registry.

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

1. 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 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. 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.
  2. Run a full system scan.
  3. If any files are detected as infected with VBS.Kasnar, click Delete.
3. Deleting all text files that the Trojan created
Follow the instructions for your operating system:
  • Windows 95/98/Me/NT/2000
    1. Click Start, point to Find or Search, and then click Files or Folders.
    2. Make sure that "Look in" is set to (C:) and that "Include subfolders" is selected.
    3. Type *.txt in the "Named" or "Search for..." box.
    4. Click Find Now or Search Now.
    5. Click the Name column header to sort the files by name.
    6. Look for files named <number>.txt in the following folders:

      C:\
      C:\Windows
      C:\Windows\System32
      C:\Program Files\KaZaA\KaZaA Lite\my shared folder
      A:\
    7. Delete all <number>.txt files that you are sure are not associated with any other activity.

      NOTE:
      An easy way to determine whether a text file was created by the Trojan is to look at the Modified Date and Size columns in the Search box. Though the actual size of the files is 116 bytes, the Search box will display the size as 1 KB. You can verify the exact size by right-clicking the file name and then clicking Properties.
  • Windows XP
    1. Click Start, and then click Search.
    2. Click All files and folders.
    3. Type *.txt in the "All or part of the file name" box.
    4. Verify that "Look in" is set to "Local Hard Drives" or to (C:).
    5. Click "More advanced options."
    6. Select "Search system folders."
    7. Select "Search subfolders."
    8. Click Search.
    9. Click the Name column header to sort the files by name.
    10. Look for files named <number>.txt in the following folders:

      C:\
      C:\Windows
      C:\Windows\System32
      C:\Program Files\KaZaA\KaZaA Lite\my shared folder
      A:\
    11. Delete all <number>.txt files that you are sure are not associated with any other activity.

      NOTE:
      An easy way to determine whether a text file was created by the Trojan is to look at the Modified Date and the Size column in the Search box. Though the actual size of the files is 116 bytes, the Search box will display the size as 1 KB. You can verify the exact size by right-clicking the file name and clicking Properties.

4. Deleting the values 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 the specified keys only. Read the document "How to make a backup of the Windows registry " for instructions.
  1. Click Start, and then 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_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
  4. In the right pane, delete the value:

    MSrundll32 sysops.vbs
  5. Navigate to the key:

    HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion
  6. In the right pane, modify the value data of the value name RegisteredOwner. You may change it to any value you want, including your login name.
  7. Exit the Registry Editor.


Writeup By: Yana Liu