VBS.Moon@mm

SUMMARY

VBS.Moon@mm is a VBScript threat which is similar to VBS.Loding.A@mm; it makes use of JS.Exception.Exploit to run its instructions to distribute itself to others using Microsoft Outlook and mIRC. The propagation is a link to a Web site, which downloads the mass-mailing script and executes it.

Protection

• Virus Definitions (LiveUpdate™ Weekly) April 17, 2002
• Virus Definitions (Intelligent Updater) April 15, 2002

TECHNICAL DETAILS

This VBScript threat may arrive by email in a simple form. The email message is composed in HTML format and uses an Iframe exploit to open your Web browser to a particular Web page within the http:/ /utenti.quipo.it domain. That Web page runs an HTML script, which downloads a .vbs file to your computer.

Depending on the variant of this script--there are three known variants--the newly created .vbs file will check one of the following registry entries to see whether a marker value of "1" has been set:

A variant: HKEY_CURRENT_USERsoftwaremoonexplorerb
B variant: HKEY_CURRENT_USERsoftwaremoonexplorerx
C variant: HKEY_CURRENT_USERsoftwaremoonexplorer98

If the script does not find the marker value, it assumes that the host system has not been infected, and it does the following:

1. It copies itself to the Windows folder as Syashin#.vbs
   
   NOTE: This file name will vary depending on the variant of the worm. The # could be any number or character.
   
2. It adds the value
   
   explorer     WindowsSyashin#.vbs
   
   to the registry key
   
   HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindowsCurrentVersionRun
   
   This cause the file that it copied in step 1 to run when you start Windows.
3. Next, it attempts to send itself using Microsoft Outlook. It uses code which slightly resembles that of VBS.LoveLetter. The email is composed in HTML format and is sent only if the following registry entry is not set to "1":
   
   HKEY_CURRENT_USERSoftwareMicrosoftWAB
   
   The format of the email message is as follows:
   
   Subject: Hi
   Message (in HTML): KONO SYASHIN MITE NE !!!!<Iframe html tag **URL Deleted**>
   Attachment: Syashin#.vbs
   
4. The script then searches for standard folders that contain mIRC chat configuration files; if it find such files, it overwrites the existing Script.ini file in an effort to send a copy of the script to others.
5. The script then sets the Internet Explorer home page to a now defunct Web page in the http:/ /it.geocities.com domain.

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

To remove this Trojan:

1. Update the virus definitions, run a full system scan, and delete all files that are detected as VBS.Moon@mm
2. Delete the value
   
   explorer     WindowsSyashin#.vbs
   
   from the registry key
   
   HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindowsCurrentVersionRun
   
3. Reset the Internet Explore home page.

For details on how to do this, read the following instructions.

To scan with Norton AntiVirus and delete the Trojan files:

1. Obtain the most recent virus definitions. There are two ways to do this:
   • Run LiveUpdate. LiveUpdate is the easiest way to obtain virus definitions. These virus definitions have undergone full quality assurance testing by Symantec Security Response and 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 have undergone full quality assurance testing by Symantec Security Response. They 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.
2. Start Norton AntiVirus (NAV), and make sure that NAV is configured to scan all files.
   • NAV Consumer products: Read the document How to configure Norton AntiVirus to scan all files.
   • NAV Enterprise products: Read the document How to verify a Symantec Corporate antivirus product is set to scan All Files.
3. Run a full system scan.
4. Delete all files that are detected as VBS.Moon@mm. Replace the deleted Script.ini file from a clean backup or reinstall mIRC.

To remove 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 following key:
   
   HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindowsCurrentVersionRun
   
4. In the right pane, delete the following value:
   
   explorer     WindowsSyashin#.vbs
   
5. Click Registry, and click Exit.

To reset the Internet Explorer home page:

1. Start Microsoft Internet Explorer.
2. Connect to the Internet, and go to the page that you want to set as your home page.
3. Click Tools, and then click Internet Options.
4. In the Home page section of the General tab, click Use Current, and then click OK.