Backdoor.NetCrack.B

SUMMARY

Backdoor.NetCrack.B is a Backdoor Trojan horse that gives an attacker unauthorized access to an infected computer. It can be programmed to perform different actions. Depending on how it was programmed, the Trojan may use different .dll files.

This Trojan horse is created using the NetCrack Trojan creator. Refer to the Technical Description section for a picture of the NetCrack program interface.

Protection

• Virus Definitions (LiveUpdate™ Weekly) April 14, 2004
• Virus Definitions (Intelligent Updater) April 13, 2004

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
• Compromises Security Settings: Allows unauthorized remote access.

Distribution

• Distribution Level: Low
• Ports: TCP 777 and 778

TECHNICAL DETAILS

When Backdoor.NetCrack.B is executed, it does the following:

1. Copies itself to %System%Mswin.exe.
   
   
2. Listens on TCP ports 777 and 778.
   
   
3. Establishes a connection with the attacker through a password-protected authorization.
   
   It allows the attacker to do any of the following:
   
   • Get system and network information, including login names and cached network passwords
   • Install an FTP server that allows the attacker to use the computer as a temporary storage device
   • Print text, play media files, and open or close the CD-ROM drive
   • Hide icons, the system tray, buttons, and the taskbar
   • Switch the monitor off and on
   • Intercept confidential information by hooking any keystrokes
   • Intercept information that is currently displayed on the screen
   • Manage the installation of the backdoor Trojan
   • Download and execute files
   • Alter many system parameters, such as screen resolution and system colors
     
     
4. Depending on which plugins the attacker added, the Trojan can also:
   
   • Take screenshots
   • Proxy HTTP
   • Set up a Telnet server
     
     
5. Creates and adds subkeys to the registry key:
   
   HKEY_LOCAL_MACHINESOFTWARENetCrack
   
   
6. Modifies the value to:
   
   "Shell"="Explorer.exe mswin.exe"
   
   in the registry key:
   
   HKEY_LOCAL_MACHINESoftwareMicrosoftWindows NTCurrentVersionWinlogon
   
   so that the Trojan runs when you start Windows NT/2000/XP.
   

The picture of the program that is used to create the Trojan follows:

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

The following instructions pertain to all current and recent Symantec antivirus products, including the Symantec AntiVirus and Norton AntiVirus product lines.

1. Disable System Restore (Windows Me/XP).
2. Update the virus definitions.
3. Do one of the following:
   • Windows 95/98/Me: Restart the computer in Safe mode.
   • Windows NT/2000/XP: End the malicious process.
4. Run a full system scan and delete all the files detected as .
5. Reverse the changes made to the registry.
   

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

1. To disable System Restore (Windows Me/XP)
If you are running Windows Me or Windows XP, we recommend that you temporarily turn off System Restore. Windows Me/XP uses this feature, which is enabled by default, to restore the files on your computer in case they become damaged. If a virus, worm, or Trojan infects a computer, System Restore may back up the virus, worm, or Trojan on the computer.

Windows prevents outside programs, including antivirus programs, from modifying System Restore. Therefore, antivirus programs or tools cannot remove threats in the System Restore folder. As a result, System Restore has the potential of restoring an infected file on your computer, even after you have cleaned the infected files from all the other locations.

Also, a virus scan may detect a threat in the System Restore folder even though you have removed the threat.

For instructions on how to turn off System Restore, read your Windows documentation, or one of the following articles:

• "How to disable or enable Windows Me System Restore"
• "How to turn off or turn on Windows XP System Restore"

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Note: When you are completely finished with the removal procedure and are satisfied that the threat has been removed, re-enable System Restore by following the instructions in the aforementioned documents.

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For additional information, and an alternative to disabling Windows Me System Restore, see the Microsoft Knowledge Base article, "Antivirus Tools Cannot Clean Infected Files in the _Restore Folder," Article ID: Q263455.

2. To update 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 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).
• 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).
  
  The Intelligent Updater virus definitions are available: Read "How to update virus definition files using the Intelligent Updater" for detailed instructions.

3. To restart the computer in Safe mode or end the malicious process

Windows 95/98/Me
Shut down the computer and turn off the power. Wait for at least 30 seconds, and then restart the computer in Safe mode. For instructions, read the document, "How to start the computer in Safe Mode."

Windows NT/2000/XP
To end the malicious process:
1. Press Ctrl+Alt+Delete once.
2. Click Task Manager.
3. Click the Processes tab.
4. Double-click the Image Name column header to alphabetically sort the processes.
5. Scroll through the list and look for Mswin.exe.
6. If you find the file, click it, and then click End Process.
7. Exit the Task Manager.
   

4. To scan for and delete 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.NetCrack.B, click Delete.

5. To reverse the changes made to the registry

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WARNING: Symantec strongly recommends that you back up the registry before making 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.

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1. Click Start, and then click Run. (The Run dialog box appears.)
2. Type regedit
   
   Then click OK. (The Registry Editor opens.)
   
   
3. Navigate to the key:
   
   HKEY_LOCAL_MACHINESOFTWARE
   
   
4. In the left pane, delete the subkey:
   
   NetCrack
   
   
5. Do one of the following:
   • Windows 95/98/Me. Skip to step i.
   • Windows NT/2000/XP. Proceed with step f.
     
     
6. Navigate to the key:
   
   HKEY_LOCAL_MACHINESoftwareMicrosoftWindows NTCurrentVersionWinlogon
   
   
7. In the right pane, double-click:
   
   Shell
   
   
8. Delete:
   
   mswin.exe
   
   so that the text in the Value date box is:
   
   Explorer.exe
   
   
9. Exit the Registry Editor.
   
   
10. If you were working in Safe mode, restart the computer in Normal mode. For instructions, read the section on returning to Normal mode in the document, "How to start the computer in Safe Mode."