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VBS.LoveLetter.CH

VBS.LoveLetter.CH

Discovered:
21 March 2001
Updated:
13 February 2007
Also Known As:
VBS/Linda.A, VBS.Vbswg2.gen
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This worm sends itself to email addresses in the Microsoft Outlook address book and also spreads to Internet chatrooms using mIRC. This worm overwrites files on local and remote drives, including files with the extensions .vbs, .vbe, .js, .jse, .css, .wsh, .sct, .hta, .jpg, .jpeg, .wav, .txt, .gif, .doc, .htm, .html, .xls, .ini, .bat, .com, .avi, .qt, .mpg, .mpeg, .cpp, .c, .h, .swd, .psd, .wri, .mp3, and .mp2.

The contents of most of these files are replaced with the source code of the worm, destroying the original contents. The worm also appends the .vbs extension to each of these files. For example, image.jpg becomes image.jpg.vbs.

Antivirus Protection Dates

  • Initial Rapid Release version 21 March 2001
  • Latest Rapid Release version 08 August 2016 revision 023
  • Initial Daily Certified version 21 March 2001
  • Latest Daily Certified version 09 August 2016 revision 001
  • Initial Weekly Certified release date pending
Click here for a more detailed description of Rapid Release and Daily Certified virus definitions.

When executed, the worm does the following:
  1. Copies itself to the \Windows\System folder as XMLDriver32.dll.vbs.
  2. For each drive, including network drives, the worm attempts to infect files that have .vbs and .vbe extensions.
  3. The worm overwrites all files having the extensions .js, .jse, .css, .wsh, .sct, .hta, .jpg, and .jpeg with viral code. It then makes a copy of the file and adds the extension .vbs to the file name. For example, if the file is named House_pics.jpg, the overwritten file is named House_pics.jpg.vbs. The original file is then deleted. These files must be deleted and then restored from a backup.

    CAUTION: Do not attempt to run files that have been overwritten or renamed by this worm. If you do, the worm is executed again.
  4. The worm also spreads by way of mIRC by creating a Script.ini file in the mIRC program folder. The script file sends the original file to other users in the chatroom.
  5. The worm uses MAPI calls to the Microsoft Outlook program and creates messages by going through all of the addresses in the Microsoft Outlook Address Book. The worm uses the Windows registry to keep track of those who have been sent the message, so that each is sent only one email.

    Subject: Important message for <username>

    Message: This is the attached file you asked from me. Attached to the message is the original file.

    The subject <username> is the name of the person who is receiving the message.


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.

If any files were infected by the worm--and have had the .vbs extension appended, as described in the Technical Description section--you must delete them and restore them from a backup.

CAUTION: Do not attempt to run files that have been overwritten or renamed by this worm. If you do, the worm is executed again.

Writeup By: Douglas Knowles