Backdoor.Backage

SUMMARY

Backdoor.Backage is a backdoor Trojan horse that allows unauthorized access to a compromised computer. This Trojan horse originated in Europe and has not been reported to be in the Wild.

Backdoor.Backage is written in Visual Basic. The default ports are 5333 (TCP) and 411(TCP).

Protection

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

TECHNICAL DETAILS

Backdoor.Backage has a standard client/server backdoor architecture. Early versions of the Trojan do not allow the entry port to be configured; although, later versions do allow for this.

When Backdoor.Backage is executed, it does the following:

1. Moves itself to the %Windir% folder as either Mskernel16.exe or WinStop32.exe, depending on the version of the Trojan.
   
   NOTE: %Windir% is a variable. The Trojan locates the Windows installation folder (by default, this is C:Windows or C:Winnt) and moves itself to that location.
   
2. Adds one of these values:
   
   Internet Explorer Plugin %Windir%Mskernel16.exe
   
   Internet Explorer Plugin %Windir%WinStop32.exe
   
   to the registry key:
   
   HKEY_LOCAL_MACHINESoftwareMicrosoftWindowsRun
   
   so that the Trojan runs when you start Windows.
   
3. May add one of these values:
   
   Internet Explorer Plugin %Windir%Mskernel16.exe
   
   Internet Explorer Plugin %Windir%WinStop32.exe
   
   to these registry keys:
   
   HKEY_LOCAL_MACHINESoftwareMicrosoftWindowsRunOnce
   
   HKEY_LOCAL_MACHINESoftwareMicrosoftWindowsRunServices
   
   so that the Trojan runs when you start Windows.
   
4. Adds one of these lines:
   
   run=Mskernel16.exe
   
   run=WinStop32.exe
   
   to the [Windows] section of the Win.ini file.
   
   so that the Trojan runs when you start Windows 95/98/Me.
   
5. Modifies the System.ini, by appending one of these lines of text to the end of the shell = line:
   
   Mskernel16.exe
   
   WinStop32.exe
   
   so that the Trojan runs when you start Windows.

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

These instructions pertain to 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 the files detected as Backdoor.Backage.
3. Reverse the changes that the Trojan made to the registry.
4. Reverse the changes the Trojan made to the Win.ini and System.ini files (Windows 95/98/Me only).

For specific details on each of these procedures, read the following instructions.

1. Updating the virus definitions
Symantec Security Response fully tests all the virus definitions for quality assurance before they are posted to our servers. There are two ways to obtain the most recent virus definitions:

• Running LiveUpdate, which is the easiest way to obtain the virus definitions. These virus definitions are posted to the LiveUpdate servers once each week (usually on Wednesdays), unless there is a major virus outbreak. To determine whether definitions for this threat are available by LiveUpdate, refer to the Virus Definitions (LiveUpdate), in the "Protection" section, at the top of this writeup.
• Downloading the definitions using the Intelligent Updater. The Intelligent Updater virus definitions are posted on U.S. business days (Monday through Friday). You should download the definitions from the Symantec Security Response Web site and manually install them. To determine whether definitions for this threat are available by the Intelligent Updater, refer to the Virus Definitions (Intelligent Updater), in the "Protection" section, at the top of this writeup.
  
  The 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. Scanning for and deleting the infected files

1. Start your Symantec antivirus program and make sure that it is configured to scan all the files.
   • For Norton AntiVirus consumer products: Read the document, "How to configure Norton AntiVirus to scan all files."
   • For Symantec AntiVirus Enterprise products: Read the document, "How to verify that 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 Backdoor.Backage, click Delete.

3. Reversing the changes that the Trojan made 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 the specified keys only. Read the document, "How to make a backup of the Windows registry," for instructions.

1. Click Start, and then click Run. (The Run dialog box appears.)
2. Type regedit, and then click OK. (The Registry Editor opens.)
3. Navigate to each of these keys:
   
   HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindowsCurrentVersionRun
   
   HKEY_LOCAL_MACHINESoftwareMicrosoftWindowsRunOnce
   
   HKEY_LOCAL_MACHINESoftwareMicrosoftWindowsRunServices
   
   
4. In the right pane of each key, delete any value that refers to:
   
   Internet Explorer Plugin
   
5. Exit the Registry Editor.

4. Reversing the changes that the Trojan made to the Win.ini and System.ini files
This is necessary only on Windows 95/98/Me computers.

Note for Windows Me users only: Due to the file-protection process in Windows Me, a backup copy of Win.ini exists in the C:WindowsRecent folder. Symantec recommends that you delete this file before you continue with the steps in this section. To do this using Windows Explorer, go to C:WindowsRecent, and in the right pane select the Win.ini file and delete it. The Win.ini file will be recreated in C:WindowsRecent when you save your changes to Win.ini in C:Windows.

1. Click Start, and then click Run.
2. Type the following, and then click OK.
   
   edit c:windowswin.ini
   
   The MS-DOS Editor opens.
   
   NOTE: If Windows is installed in a different location, make the appropriate path substitution.
   
3. In the [windows] section of the file, look for an entry similar to one of the following:
   
   run=Mskernel16.exe
   
   run=WinStop32.exe
   
4. Select the entire line. Be sure that you have not selected any other text, and then press Delete.
5. Click File, and then click Save.
6. Click File, and then click Exit.
7. Click Start, and then click Run.
8. Type the following, and then click OK.
   
   edit c:windowssystem.ini
   
9. The MS-DOS Editor opens.
   
   NOTE: If Windows is installed in a different location, make the appropriate path substitution.
   
10. In the [boot] section of the file, look for one of these lines:
    
    shell=explorer.exe Mskernel16.exe
    
    shell=explorer.exe WinStop32.exe
    
11. Change the line to:
    
    shell=explorer.exe
    
    NOTE: If you use a different or customized shell, make the appropriate changes.
    
12. Click File, and then click Save.
13. Click File, and then click Exit.