W32.Brid.A@mm

SUMMARY

Due to a decreased rate of submissions, Symantec Security Response has downgraded this threat from a Category 3 to a Category 2 as of May 5, 2003.

W32.Brid.A@mm is a mass-mailing worm that includes a slightly modified variant of W32.FunLove.4099. When W32.Brid.A@mm runs, it attempts to insert several files onto the system and mass-mail itself. The worm contains its own SMTP engine, and it attempts to obtain the address of the email server and contact it directly. The email message has the following characteristics:
Subject: [Registered Windows company name]
Attachment: Readme.exe

The worm uses a known exploit in Internet Explorer, Incorrect MIME Header can cause IE to Execute E-mail attachment.

NOTE: Symantec antivirus products will detect the W32.Funlove.4099 virus component with definitions that have dates of November 8, 1999, or later.

Behavior

Symptoms

Transmission

Protection

• Virus Definitions (LiveUpdate™ Weekly) November 4, 2002
• Virus Definitions (Intelligent Updater) November 4, 2002

Threat Assessment

Wild

• Wild Level: Low
• Number of Infections: More than 1000
• Number of Sites: More than 10
• Geographical Distribution: Medium
• Threat Containment: Easy
• Removal: Moderate

Damage

• Damage Level: Medium
• Large Scale E-mailing: Emails everyone in the Microsoft Outlook Adress Book, and addresses that if finds in .htm and .dbx files.
• Deletes Files: MSconfig.exe in the %system% folder will be overwritten by the worm
• Degrades Performance: If the virus and/or worm is active in memory, the computer will become slow, and may stop responding occasionally
• Causes System Instability: If the worm is active in memory, the computer may crash and/or become completly unresponsive to any commands.

Distribution

• Distribution Level: High
• Subject of Email: Company name as registered in Windows or the same name as in the To: field.
• Name of Attachment: Readme.exe
• Size of Attachment: 114,687 Bytes
• Shared Drives: W32.Funlove.4099 infects files on shared drives

TECHNICAL DETAILS

When this worm runs, it first attempts to connect to www.hotmail.com. If the worm is unable to connect, a short delay occurs before the worm continues its malicious actions.

Next, the worm inserts several files onto the system, modifies the Windows registry, runs the slightly modified variant of W32.Funlove.4099, and emails itself to all contacts in the Microsoft Outlook Address Book.

File Insertion
The worm insert several files on the computer.

It copies these files to the Windows desktop:

• Help.eml
• Explorer.exe

Help.eml is a Microsoft Outlook Express file. If this file is opened on an unpatched system, the attachment (which is the worm) runs automatically. This is due to the use of the known exploit, Incorrect MIME Header can cause IE to Execute E-mail attachments.

Explorer.exe is a copy of the worm.

W32.Brid.A@mm also creates these files:

• %system%Bride.exe
• %system%Msconfig.exe
• %system%Regedit.exe

NOTE: %system% is a variable. The worm locates the System folder and copies itself to that location as %system%Regedit.exe. By default this is C:WindowsSystem (Windows 95/98/Me), C:WinntSystem32 (Windows NT/2000), or C:WindowsSystem32 (Windows XP).

%system%Bride.exe and %system%Msconfig.exe contains the virus W32.Funlove.4099. The worm executes this file.

Registry modification
The worm adds the value

regedit %system%egedit.exe

to the registry key

HKEY_CURRENT_USERSOFTWAREMicrosoftWindowsCurrentVersionRun

so that the worm runs each time that you start Windows.

It also adds three keys under

HKEY_LOCAL_MACHINESoftwareMicrosoftWindows
CurrentVersionExplorerRemoteComputer

Virus insertion
This worm contains a slightly modified variant of W32.Funlove.4099. The worm attempts to execute this virus. The main difference between this variant of the virus and the original W32.Funlove.4099 is the file name that is uses. This variant uses the file name Bride.exe instead of Flcss.exe.

For further information, please refer to the W32.Funlove.4099 write-up.

NOTE: Symantec antivirus products will detect the W32.Funlove.4099 virus component with definitions that have dates of November 8, 1999, or later.

Email routine
The worm contains its own SMTP engine, and it attempts to find and contact the email server directly.

It attempts to email everyone in the Microsoft Outlook Address Book, as well as any email address it may find inside .htm and .dbx files. The email message that this worm sends will appear as follows:

From: [Registered Windows user name]

NOTE: The text in the "From:" field may, in some cases, be identical to the text in the "To:" field.

Subject: [Registered Windows company name]
Message Body:
Hello,

Product Name: [Windows Version]
Product ID: [Windows ID]
Product Key: [Key]
Process List: [List of processes]

Thank you.

All of the information inside the brackets is taken from the infected computer. The worm is attached to the email message, and if the email message is viewed on an unpatched system, the worm will run automatically.

For further information about this exploit, please see the Microsoft Security Bulletin.

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

NOTES:

• These instructions are for all current and recent Symantec antivirus products, including the Symantec AntiVirus and Norton AntiVirus product lines.
• Whether you remove this threat manually or by using the removal tool, on Windows 98/Me computers, it is likely that the worm has overwritten the Windows file Msconfig.exe. Although this file is not necessary for Windows to function, it is a useful tool, and should be replaced from a clean backup or reinstalled.

Removal using the removal tool
Symantec Security Response has provided a free tool to remove infections of W32.Brid.A@mm, W32.Funlove.4099, and W32.Funlove.int. This is the easiest way to do this. For complete instructions on how to obtain and use the W32.Brid.A@mm/W32.Funlove.4099 Removal Tool, click here.


Manual removal

NOTE: Do this in the order shown. On Windows 95/98/Me computers, if you run (the legitimate Windows file) Regedit.exe (step 4) before you remove the copy that the worm placed in the%system% folder, it will run the copy that the worm created.

1. Update the virus definitions.
2. Restart the computer in Safe mode.
3. Run a full system scan, and repair all files that are detected as W32.Funlove.4099. Delete all files detected as W32.Brid.A@mm or W32.Funlove.int.
4. Delete the value
   
   regedit
   
   that the worm added to the registry key
   
   HKEY_CURRENT_USERSOFTWAREMicrosoftWindowsCurrentVersionRun
   

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 once 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 restart the computer in Safe mode:
All Windows 32-bit operating systems, except Windows NT, can be restarted in Safe mode. For instructions on how to do this, read the document How to start the computer in Safe Mode.

To scan for and repair the infected files:

1. Start your Symantec antivirus software and make sure that it is configured to scan all files.
   • Norton AntiVirus consumer products: Read the document How to configure Norton AntiVirus to scan all files.
   • Symantec enterprise antivirus products: Read the document How to verify a Symantec Corporate antivirus product is set to scan All Files.
2. Run a full system scan.
3. If any files are detected as infected with W32.Funlove.4099, click Repair.
4. If any files are detected as infected with W32.Funlove.int or W32.Brid.A@mm, click Delete.

To remove the value that the worm added to 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_CURRENT_USERSOFTWAREMicrosoftWindowsCurrentVersionRun
   
4. In the right pane, delete the value
   
   regedit
   
5. Exit the Registry Editor.