Backdoor.Zvrop

SUMMARY

The Backdoor.Zvrop backdoor Trojan allows unauthorized access to the infected computer. It copies itself to the %System% folder as these files:

• RegeditExec.exe
• WinLogin.exe

The default ports on which the server listens are 4,527, 3,527, and 2,527.

Protection

• Virus Definitions (LiveUpdate™ Weekly) February 5, 2003
• Virus Definitions (Intelligent Updater) January 30, 2003

Threat Assessment

Wild

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

Damage

• Damage Level: Medium
• Compromises Security Settings: Allows unauthorized access to an infected computer

Distribution

• Distribution Level: Low
• Ports: 4527, 3527, 2527

TECHNICAL DETAILS

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

1. Copies itself as the following files:
   
   • %System%RegeditExec.exe
   • %System%WinLogin.exe
     
     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).
     
     
2. Adds the value:
   
   RegeditExec %System%RegeditExec.exe
   
   to the registry key:
   
   HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindowsCurrentVersionRun
   
3. Listens on ports 4,527, 3,527, and 2,527 for connections from the client software. The client software can perform many unwanted actions on your computer, including remote execution, deletion, key logging, and program uploading.
   
4. Creates the data files:
   • %System%RegeditExec.dat
   • %System%WinLogin.dat
     
     These files are not malicious and will not be detected.

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 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: End the Trojan process.
3. Run a full system scan and delete all the files detected as Backdoor.Zvrop.
4. Reverse the changes that the Trojan made to the registry.
5. Find and delete the data files created by the Trojan, using the Windows Find or Search utility.
   

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. 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 RegeditExec.exe and WinLogin.exe.
6. If you find the files, 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.Zvrop, click Delete.

4. Reversing the changes 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 the key:
   
   HKEY_LOCAL_MACHINESoftwareMicrosoftWindowsCurrentVersionRun
   
4. In the right pane, delete the value
   
   RegeditExec %System%RegeditExec.exe
   
5. Exit the Registry Editor.

5. Finding and deleting files using the Windows Find or Search utility

Follow the instructions for your operating system:

Windows 95/98/Me/NT/2000

1. Click Start, point to Find or Search, and then click Files or Folders.
2. Make sure that "Look in" is set to (C:) and that "Include subfolders" is checked.
3. In the "Named" or "Search for..." box, type, or copy and paste, the file name:
   
   regeditexec.dat winlogin.dat
   
4. Click Find Now or Search Now.
5. Delete the displayed files.

Windows XP

1. Click Start, and then click Search.
2. Click All files and folders.
3. In the "All or part of the file name" box, type, or copy and paste, the file name:
   
   regeditexec.dat winlogin.dat
   
4. Verify that "Look in" is set to "Local Hard Drives," or to (C:).
5. Click "More advanced options."
6. Check "Search system folders."
7. Check "Search subfolders."
8. Click Search.
9. Delete the displayed files.