Threat Explorer

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VBS.Krim.C

VBS.Krim.C

Discovered:
20 October 2002
Updated:
13 February 2007
Systems Affected:
Windows

VBS.Krim.C copies itself as Valentina.jpg.vbs to all logical and network drives, including drive A. The worm also spreads through IRC as Valentina.htm. This worm has three payloads, one of which formats drive C if the right condition is met.

This worm is a Visual Basic Script (VBS); its payloads can format drive C and delete .doc files.

When the worm runs, it does the following:

It copies itself as %system%\WinLoader.vbs and %system%\Valentina.vbs.

NOTE: %system% is a variable. The worm locates the System folder and copies itself to that location. By default this is C:\Windows\System (Windows 95/98/Me), C:\Winnt\System32 (Windows NT/2000), or C:\Windows\System32 (Windows XP).

It adds the value

WinLoader   %system%\WinLoader.vbs

to one of these registry keys

HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run
HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Run

It then copies itself as Valentina.jpg.vbs to the root of all logical and network drives, including drive A.

The worm then creates the file %system%\Valentina.htm, which is the HTML version of the worm. It then searches for all .htm files on drive C. It prepends the <!--Valentina--> tag to the files that it finds.

The worm also creates the file %system%\Valentina.log, which is a log file that the worm uses. It is not infected, and therefore is not detected by Symantec antivirus products. Delete this file if you find it.

Next, the worm searches for .vbs and .vbe files and overwrites them with itself. It also searches for .mp3 and .txt files. If it finds a file that has an .mp3 or .txt extension, it makes a copy of itself as the file name that it found, but with the .vbs extension appended to it. It changes the attribute of the original .mp3 or .txt files to hidden. For example, if the worm finds the file Readme.txt, it hides the original file and makes a copy of itself as Readme.txt.vbs.

The worm also appends this text to all .bat files:

Rem Valentina I Love You

The worm then creates the file Script.ini in the C:\Mirc folder. If IRC is installed, Script.ini, which is an IRC worm, sends VBS.Krim.C to IRC users as a file named Valentina.htm.

The worm then executes three payloads if the right criteria are met.

Payload 1
On October 10 of every year, the worm picks a random number from 1 to 1000. If the random number is 1, it overwrites C:\Autoexec.bat with commands to format drive C and then restarts the system. This will reformat drive C on Windows 95/98/Me-based computers.

Payload 2
The worm picks a random number from 1 to 500. If the number is 7, the worm deletes all .doc files from the infected system.

Payload 3
On February 14 of any year, the worm enters a loop that continuously displays this message:

***VALENTINA I LOVE YOU***

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.

NOTE: These instructions are for 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 files that are detected as VBS.Krim.C.
  3. On Windows 95/98/Me, delete C:\Autoexec.bat and restore it from a clean backup if it was overwritten by the worm. Delete the file %system%\Valentina.log if it exists. Restore deleted .doc files and overwritten .vbs files, if necessary.
  4. Delete the value

    WinLoader   %system%\WinLoader.vbs

    from the registry key

    HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run

    or

    HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Run
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.
  2. Run a full system scan.
  3. If any files are detected as infected with VBS.Krim.C, click Delete.

To delete and replace files
  1. Start Windows Explorer.
  2. If you are running Windows 95/98/Me, and payload 1 activated on October 10, delete C:\Autoexec.bat and restore it from a clean backup.
  3. Delete %system%\Valentina.log if it exists.
  4. Restore deleted .doc files and overwritten .vbs files, if necessary.

To delete 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 key

    HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
  4. In the right pane, delete the value

    WinLoader     %system%\WinLoader.vbs
  5. Exit the Registry Editor.


Writeup By: Gor Nazaryan