Backdoor.Death

SUMMARY

Backdoor.Death is a typical Backdoor Trojan, which gives a remote attacker unobstructed access to your computer.

Protection

• Virus Definitions (LiveUpdate™ Weekly) August 22, 2001
• Virus Definitions (Intelligent Updater) August 18, 2001

Threat Assessment

Wild

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

Damage

• Damage Level: Medium

Distribution

• Distribution Level: Low

TECHNICAL DETAILS

The backdoor Trojans in this family typically add keys or values to these registry keys:

HKEY_LOCAL_MACHINESoftwareMicrosoftWindowsCurrentVersionRunOnce
HKEY_LOCAL_MACHINESoftwareMicrosoftWindowsCurrentVersionRun
HKEY_LOCAL_MACHINESoftwareMicrosoftWindowsCurrentVersionRunServicesOnce
HKEY_LOCAL_MACHINESoftwareMicrosoftWindowsCurrentVersionsockets

They may also add load and run lines to the following system files:

C:Windowswin.ini
C:Windowssystem.ini

Version 26
Backdoor.Death (v26) does the following:

Registry changes

• Adds the value
  
  winfont.exe C:WindowsFONTSwinfont.exe
  
  to the registry key
  
  HKEY_LOCAL_MACHINESoftwareMicrosoftWindowsCurrentVersionRunOnce
  
• Adds the values
  
  internat.exe internat.exe
  winfont.exe    C:WindowsFONTSwinfont.exe
  
  to the registry key
  
  HKEY_LOCAL_MACHINESoftwareMicrosoftWindowsCurrentVersionRun
  
• Adds the value
  
  winfont.exe C:WindowsFONTSwinfont.exe
  
  to the registry key
  
  HKEY_LOCAL_MACHINESoftwareMicrosoftWindowsCurrentVersionRunServicesOnce
  
  
• Creates the registry key sockets under the registry key HKEY_LOCAL_MACHINESoftwareMicrosoftWindowsCurrentVersion.
  
  It also creates an entire subkey structure under the sockets subkey.

System file changes
The Backdoor Trojan modifies the following system files:

• C:WindowsWin.ini. It adds the following lines:
  
  load=C:WindowsFONTSwinfont.exe
  run=C:WindowsFONTSwinfont.exe

• C:WindowsSystem.ini. It adds the line:
  
  load=C:WindowsFONTSwinfont.exe

Dropped files
This Trojan creates the following files on your system:

• C:WindowsFONTSWinfont.exe
• C:WindowsSystemInternat.exe (the original is saved as C:WindowsInterface.dll, Kernel1.exe, Kernel_1.exe, Kernel2.exe, or Kernel_2.exe in the Windows Temp folder.)
• C:WindowsSystemRunexec.dll
• C:Autorun.inf
• C:WindowsAvp32.ini
• C:WindowsAvpm.ini

Version 26b
Backdoor.Death (v26.b) behaves in exactly the same manner as v26, except this version uses the value

winsock     C:WINDOWSSYSTEMwinsock.exe

instead of the value

winfont.exe      C:WindowsFONTSwinfont.exe

when it adds the values to these keys:

HKEY_LOCAL_MACHINESoftwareMicrosoftWindowsCurrentVersionRun
KEY_LOCAL_MACHINESoftwareMicrosoftWindowsCurrentVersionRunServicesOnce

Version 26c
Backdoor.Death (v26c) Backdoor.Death (v26.b) behave in exactly the same manner as v26, except this version

adds the value

winsys.exe %system%winsys.exe

to the registry key

HKEY_LOCAL_MACHINESoftwareMicrosoftWindowsCurrentVersionRun

and it creates the registry key

Socket

under the registry key

HKEY_LOCAL_MACHINESoftwareMicrosoft

This version creates the files %system%Winsys.exe and %system%Runexec.dll.

Version 25
Backdoor.Death (v25) does the following:

Registry changes

• It adds the value
  
  internat.exe internat.exe
  
  to the registry key
  
  HKEY_LOCAL_MACHINESoftwareMicrosoftWindowsCurrentVersionRun
  
• It adds the value
  
  winupdate.exe C:WindowsFONTSwinupdate.exe
  
  to the registry key
  
  HKEY_LOCAL_MACHINESoftwareMicrosoftWindowsCurrentVersionRunServicesOnce
  
• It creates the registry key
  
  socket
  
  under the registry key
  
  HKEY_LOCAL_MACHINESoftwareMicrosoft
  
  The Backdoor Trojan also creates an entire subkey structure under the socket subkey.

System file changes
It modifies the following system files:

• C:WindowsWin.ini. It adds the following lines:
  
  load=C:WindowsFONTSwinupdate.exe
  run=C:WindowsFONTSwinupdate.exe

• C:WindowsSystem.ini. It adds the line load=C:WindowsFONTSwinupdate.exe.

Dropped files
This Trojan creates the following files on your system:

• C:WindowsFONTSWinupdate.exe
• C:WindowsSystemInternat.exe (the original is saved as C:WindowsInterface.dll, Kernel1.exe, Kernel_1.exe, Kernel2.exe, or Kernel_2.exe in the C:WindowsTemp folder.)
• C:WindowsSystemRunexec.dll
• C:Autorun.inf
• C:WindowsAvp32.ini
• C:WindowsAvpm.ini

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

NOTE: These instructions are for 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.Death.
3. Reverse the changes made to the registry.
4. (Windows 95/98/Me only). Remove references to the Trojan from the Windows startup files.
   

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

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) line 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) line 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.

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 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.Death, write down the name and location of the infected file, and then click Delete.

Editing the registry

CAUTION: We strongly recommend that you back up the system registry before making any changes. Incorrect changes to the registry could result in permanent data loss or corrupted files. Make sure you modify the specified keys only. Refer to the document How to back up the Windows registry before proceeding.

NOTE: You will not find all the values or keys on all the systems.

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 and select the key HKEY_LOCAL_MACHINESoftwareMicrosoftWindowsCurrentVersionRun.
4. Refer to the list of infected files you created while following the instructions in the previous section. In the right pane, look at the entries in the Name and Data columns.
5. If you find an entry that refers to a file that was detected as infected, select the entry, press Delete, and then click Yes to confirm.
6. Repeat steps 3 to 5 for the following registry keys:
   
   HKEY_LOCAL_MACHINESoftwareMicrosoftWindowsCurrentVersionRunOnce
   
   HKEY_LOCAL_MACHINESoftwareMicrosoftWindowsCurrentVersionRunServicesOnce
   
7. Navigate to and select the key HKEY_LOCAL_MACHINESoftwareMicrosoftWindowsCurrentVersion.
8. Under this key, look for the Sockets subkey. If it exists, delete it.
9. Navigate to and select the key HKEY_LOCAL_MACHINESoftwareMicrosoft.
10. Under this key, look for the Socket subkey. If it exists, delete it.
11. Exit the Registry Editor.
    

Removing references to the Trojan from the Windows startup files

NOTES:

• The instructions in this section applies to Windows 95/98/Me only. It is not necessary to do this if you are running Windows NT/2000/XP
• For Windows Me users only: Due to the file-protection process in Windows Me, there is a backup copy of the file that you are to edit in the C:WindowsRecent folder. We recommend that you delete this file before you continue with the steps in this section. To do so using Windows Explorer, go to the C:WindowsRecent folder, and in the right pane delete the Win.ini file. It will be regenerated as a copy of the file that you are to edit when you save your changes to that file.

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.
   
   CAUTION: The steps that follow instruct you to remove text from the load= and run= lines of the Win.ini file. If you are using older programs, they may be loading at the time of startup from one of these lines. Make sure that you remove only the lines shown.
   
3. Locate the load= and run= lines within the [windows] section of the Win.ini file; this section is usually located near the top of the file.
4. Check to see whether these lines look like the following:
   
   load=C:WindowsFONTSwinfont.exe
   run=C:WindowsFONTSwinfont.exe
   
5. If they do, for each line do the following:
   1. Position the cursor immediately to the right of the equal (=) sign.
   2. Press Shift+End to select all the text to the right of the equal sign, and then press Delete.
6. Click File, click Exit, and then click Yes when you are prompted to save the changes.
7. Click Start, and then click Run.
8. Type the following, and then click OK.
   
   edit c:windowssystem.ini
   
   The MS-DOS Editor opens.
   
   NOTE: If Windows is installed in a different location, make the appropriate substitution.
   
9. Locate the line
   
   load=C:WindowsFONTSwinfont.exe
   
   within the [boot] section of the System.ini file; the section is usually located near the top of the file.
   
10. Select, and then delete this line.
11. Click File, click Exit, and then click Yes when you are prompted to save the changes.