VBS.LoveLetter.CH

SUMMARY

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.

Protection

• Virus Definitions (Intelligent Updater) March 21, 2001

Threat Assessment

Wild

• Wild Level: Low
• Number of Infections: 0 - 49
• Number of Sites: 0 - 2
• Geographical Distribution: Low
• Threat Containment: Moderate
• Removal: Moderate

Damage

• Damage Level: Medium
• Payload Trigger: On execution of email attachment
• Payload: Overwriting files
• Large Scale E-mailing: Sends itself to all addresses in the Microsoft Outlook Address Book
• Modifies Files: Overwrites files with the following extensions: .vbs, .vbe, .js, .jse, .css, .wsh, .sct, .hta, .jpg, .jpeg, .wav, .txt, .gif, .doc, .htm, .html, .xls, .ini, .bat, .com, .mp3, and .mp2. The overwritten files can be recovered if the user is running NProtect from Norton Systemworks or Norton Utilities at the time of infection.
• Degrades Performance: Might clog the email server

Distribution

• Distribution Level: High
• Subject of Email: Important message for
• Name of Attachment: varies
• Size of Attachment: 3,876 bytes
• Shared Drives: Overwrites files located on network drives
• Target of Infection: Overwrites files with the following extensions: .vbs, .vbe, .js, .jse, .css, .wsh, .sct, .hta, .jpg, .jpeg, .wav, .txt, .gif, .doc, .htm, .html, .xls, .ini, .bat, .com, .mp3, and .mp2.

TECHNICAL DETAILS

When executed, the worm does the following:

1. Copies itself to the WindowsSystem 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":

• Turn off and remove unneeded services. By default, many operating systems install auxiliary services that are not critical, such as an FTP server, telnet, and a Web server. These services are avenues of attack. If they are removed, blended threats have less avenues of attack and you have fewer services to maintain through patch updates.
• If a blended 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 (for example, all Windows-based computers should have the current Service Pack installed.). Additionally, please apply any security updates that are mentioned in this writeup, in trusted Security Bulletins, or on vendor Web sites.
• 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.
• Configure your email server to block or remove email that contains file attachments that are commonly used to spread viruses, such as .vbs, .bat, .exe, .pif and .scr files.
• Isolate infected computers quickly to prevent further compromising your organization. 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.

REMOVAL

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.