Backdoor.Sinit

SUMMARY

Backdoor.Sinit is a Backdoor Trojan horse that gives an attacker unauthorized access to a compromised computer, by opening a random UDP port.

Backdoor.Sinit is written in the Microsoft Visual C++ programming language and is compressed with UPX.

Protection

• Virus Definitions (LiveUpdate™ Weekly) October 15, 2003
• Virus Definitions (Intelligent Updater) October 10, 2003

Threat Assessment

Wild

• Wild Level: Low
• Number of Infections: 50 - 999
• Number of Sites: More than 10
• Geographical Distribution: Low
• Threat Containment: Easy
• Removal: Moderate

Damage

• Damage Level: Medium
• Deletes Files: Deletes itself.
• Modifies Files: Drops svcinit.exe.
• Releases Confidential Info: Refer to Technical Details.
• Degrades Performance: Refer to Technical Details.
• Causes System Instability: Refer to Technical Details.
• Compromises Security Settings: Allows for unauthorized access to the computer.

Distribution

• Distribution Level: Low
• Ports: Random UDP port

TECHNICAL DETAILS

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

1. Copies itself as %System%Svcinit.exe, which runs in the background and deletes the original file.
   
   

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

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2. In Windows 95, Windows 98, and Windows Millennium Edition (Me):
   
   adds the value:
   
   "SVC Service" = "%System%svcinit.exe"
   
   to the registry key:
   
   HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindowsCurrentVersion
   RunServices
   
   so that the Trojan runs when you start Windows.
   
   
3. In Windows NT, 2000, and XP:
   
   modifies the value:
   
   "Userinit" = "%System%userinit.exe"
   
   in the registry key:
   
   HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindows NTCurrentVersion
   Winlogon
   
   so that the Trojan runs when you log on.
   
   
4. Creates the following registry key:
   
   HKEY_LOCAL_MACHINESOFTWAREMicrosoftDirectPlugin
   
   
5. Opens a random UDP port that may allow a hacker to perform any of the following actions:
   
   • Obtain computer and network information
   • Perform annoying actions
   • Intercept confidential information by hooking keystrokes
   • Download and execute files
   • Manage the installation of the Trojan
   • Alter system parameters

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. Update the virus definitions.
2. Do one of the following:
   • Windows 95/98/Me: Restart the computer in Safe mode.
   • Windows NT/2000/XP: End the Trojan process.
3. Run a full system scan and delete all the files detected as Backdoor.Sinit.
4. Reverse the changes that were made to the registry
   

For specific details on each of these steps, 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 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.
  

2. Restarting the computer in Safe mode or ending the Trojan process

Windows 95/98/Me
Restart the computer in Safe mode. All the Windows 32-bit operating systems, except for Windows NT, can be restarted in Safe mode. For instructions, read the document How to start the computer in Safe Mode.

Windows NT/2000/XP
To end the Trojan 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 "Svcinit.exe."
6. If you find the file, click it, and then click End Process.
7. Exit the Task Manager.

3. 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.Sinit, click Delete. If you are running Windows 2000 or XP, and the scan cannot delete the detected file, restart the computer in Safe mode and run the scan again.

4. Reversing 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. Do one of the following:
   
   • Windows 95/98/Me
     
     1. Navigate to the key:
        
        HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindows
        CurrentVersionRunServices
        
        
     2. In the right pane, delete the value:
        
        "SVC Service"="%System%svcinit.exe"
        
        
   • Windows NT/2000/XP:
     
     1. Navigate to the key:
        
        HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindows NTCurrentVersionWinlogon
        
     2. In the right pane, double-click the value:
        
        Userinit
        
     3. In the Value data box, delete all text to the right of the comma. Do not delete the comma itself.
        
        
        For example, on a default installation, change:
        
        
        C:WINNTsystem32userinit.exe,%System%svcinit.exe
        
        to:
        
        C:WINNTsystem32userinit.exe,
        
        
4. Navigate to and delete the registry key:
   
   HKEY_LOCAL_MACHINESOFTWAREMicrosoftDirectPlugin
   
   
5. Exit the Registry Editor.