Threat Explorer

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VBS.Krim.D@mm

VBS.Krim.D@mm

Discovered:
25 February 2003
Updated:
13 February 2007
Also Known As:
I-Worm.LoveLetter [KAV], VBS/Rimko@mm [McAfee]
Systems Affected:
Windows


VBS.Krim.D@mm is a variant of the VBS.Krim@mm worm. It sends itself to all the contacts in the Microsoft Outlook Address Book.

The email has the following characteristics:

Subject: Symantec center
Message: W32.Zokrim@mm VBS.Krim@mm VBS.krim.B VBS.krim.C delete !!!
Attachment: Vale.bat

If VBS.Krim.D@mm finds that mIRC is installed on your computer, the worm modifies the mIRC Script.ini file. This modification causes the worm to spread over the IRC network.

Antivirus Protection Dates

  • Initial Rapid Release version 25 February 2003
  • Latest Rapid Release version 28 September 2010 revision 054
  • Initial Daily Certified version 25 February 2003
  • Latest Daily Certified version 28 September 2010 revision 036
  • Initial Weekly Certified release date 26 February 2003
Click here for a more detailed description of Rapid Release and Daily Certified virus definitions.

VBS.Krim.D@mm arrives as the email attachment, Vale.bat. If this batch file is executed, it does the following:
  1. Creates the folder %Windir%\Mkz.

    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.
  2. Creates the following files:
    • C:\Vale.bat.
    • C:\Lecce.reg. VBS.Krim.D@mm sets the attribute of this file to Hidden.
    • C:\1.vbs. VBS.Krim.D@mm sets the attribute of this file to Hidden. This file displays the message "VBS.valentina@mm ???"
    • %Windir%\Mkz\Vale.bat.
    • %Windir%\Mkz\Vbs.vbs.
    • %Windir%\Commnad\Valen.bat. This file attempts to format drive C if the C:\Vale.bat file is not found.

  3. Sends itself to all the contacts in the Microsoft Outlook Address Book in an email with the following characteristics:

    Subject: Symantec center
    Message: W32.Zokrim@mm VBS.Krim@mm VBS.krim.B VBS.krim.C delete !!!
    Attachment: Vale.bat
  4. Adds the value:

    Valentina c:\vale.bat

    to the registry key:

    HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Run

    so that the worm runs when you start Windows.
  5. Renames the Windows file, %Windir%\Command\Format.com, to %Windir%\Command\Vale.com.

    NOTE: This will work on Windows 95/98/Me computers only, because the Format.com file is not found in the \Command folder under Windows NT/2000/XP.
  6. Appends the following line to the end of the C:\Autoexec.bat file:

    Valen.bat
  7. Creates the file Script.ini file. VBS.Krim.D@mm uses this file to control mIRC if mIRC is installed in any of the following folders:
    • C:\Mirc
    • C:\Mirc32
    • C:\Program Files\Mirc
    • C:\Program Files\Mirc32\

NOTES:
  • Symantec antivirus products detect Vale.bat and Vbs.vbs as VBS.Krim.D@mm.
  • The files 1.vbs, Lecce.reg, and Valen.bat are not viral and are not detected.


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.


These 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 detected as Backdoor.Snowdoor.
  3. Reverse the changes made to the registry.
  4. Remove the text that was added to the Autoexec.bat file (Windows 95/98/Me only).
  5. Rename the Format command (Windows 95/98/Me only).
  6. Restore the Script.ini if you use mIRC.

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 the 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), in the "Protection" section, at the top of this writeup.
  • 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), in the "Protection" section, at the top of this writeup.

    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 Backdoor.Snowdoor, click Delete.

3. Reversing the registry changes

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

    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: Valentina
  5. Exit the Registry Editor.


4. Removing the text that was added to the Autoexec.bat file
If you are running Windows 95/98/Me, follow these steps:
  1. The function you perform depends on your operating system:
    • Windows 95/98: Go to step b.
    • Windows Me: If you are running Windows Me, the Windows Me file-protection process may have made a backup copy of the Win.ini file that you are to edit. If this backup copy exists, it will be in the C:\Windows\Recent folder. Symantec recommends that you delete this file before you continue with the steps in this section. To do this:
      • Start Windows Explorer.
      • Browse to and select the C:\Windows\Recent folder.
      • In the right pane, select the Win.ini file and delete it. The Win.ini file will be regenerated when you save your changes to it in step f.
  2. Click Start, and then click Run.
  3. Type the following:

    edit c:\autoexec.bat/

    And then click OK.
  4. Look for the line: valen.bat
  5. If this line exists, select its entirety. Be sure that you do not select any other text, and then press Delete.
  6. Click File, and then click Save.
  7. Click File, and then click Exit.

5. Renaming the Format command
If you are running Windows 95/98/Me, follow these steps:
  1. Start Windows Explorer.
  2. Browse to and select the file:

    %Windir%\Command\Vale.com.

    NOTE: %Windir% is a variable that refers to the Windows installation folder. By default, this is C:\Windows.
  3. Select Vale.com, and then click Rename.
  4. Rename the file to Format.com

6. Restoring the Script.ini
If you use mIRC, delete the Script.ini file and replace it with a clean backup copy.


Writeup By: Koji Tabei