Backdoor.NetCrack

SUMMARY

Backdoor.NetCrack is a Backdoor Trojan that gives an attacker unauthorized access to an infected computer. By default it opens port 911 on the compromised computer. Backdoor.NetCrack is a Delphi application, packed using UPX v1.05-1.22.

Protection

• Virus Definitions (LiveUpdate™ Weekly) August 28, 2002
• Virus Definitions (Intelligent Updater) August 28, 2002

TECHNICAL DETAILS

When Backdoor.NetCrack runs, it performs the following actions:

It creates these files:

• %windir%Winx.dll
• %windir%Ddhelp.exe

NOTE: %windir% is a variable. The Trojan locates the Windows installation folder (by default this is C:Windows or C:Winnt) and copies itself to that location.

The Trojan modifies the value

Shell    Explorer.exe ddhelp

in the registry key

HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindows NTCurrentVersionWinlogon

so that it runs when you restart the computer.

Also, it may create the value (as a result of a remote administration)

runsrv    <Trojan file name>

in the registry key

HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindowsCurrentVersionRunOnce

so that the Trojan starts when you start Windows.

After Backdoor.NetCrack is installed, it establishes a connection with the hacker through a password-protected authorization.

The commands allow the hacker to perform any of the following actions:

• Deliver system and network information to the hacker, including login names and cached network passwords.
• Install an FTP server that allows the hacker to use the compromised computer as his own 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 currently displayed on the screen and deliver it to the hacker.
• Manage the installation of the backdoor Trojan.
• Download and execute files.
• Alter many system parameters, such as screen resolution and system colors.
  

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. Do one of the following:
   • Windows 95/98/Me: Restart the computer in Safe mode.
   • Windows NT/2000/XP: Stop the Trojan process that is running.
3. Run a full system scan, and delete all files that are detected as Backdoor.NetCrack.
4. Reverse the changes that the Trojan made to the registry.
   

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

To update the 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.

To restart in Safe mode or stop the process:

Windows 95/98/Me
Restart the computer in Safe mode. All Windows 32-bit operating systems, except for 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.

Windows NT/2000/XP
To stop the Trojan process:

1. Press Ctrl+Alt+Delete one time.
2. Click Task Manager.
3. Click the Processes tab.
4. Double-click the Image Name column header to sort the processes alphabetically.
5. Scroll through the list, and look for Ddhelp.exe.
6. If you find the file, click it, and then click End Process.
7. Close the Task Manager.
   

To scan for and delete the infected files:

1. Start your Symantec antivirus program, 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 Backdoor.NetCrack., click Delete.
   

To reverse 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 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_LOCAL_MACHINESOFTWAREMicrosoftWindowsCurrentVersionRunOnce
   
4. In the right pane delete the following value, if it exists:
   
   runsrv
   
5. Navigate to the key
   
   HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindows NTCurrentVersionWinlogon
   
6. In the right pane, double-click the value
   
   Shell
   
7. In the Value Data box, delete all text except for
   
   Explorer.exe
   
8. Exit the Registry Editor.