Backdoor.GWGirl

SUMMARY

Backdoor.GWGirl is a Trojan that allows unauthorized access to an infected computer.

Protection

• Virus Definitions (LiveUpdate™ Weekly) April 10, 2002
• Virus Definitions (Intelligent Updater) April 8, 2002

TECHNICAL DETAILS

Backdoor.GWGirl uses port 6267. It configures itself to run as a service.

When the Trojan is executed, it drops the following files:

• WindowsSystemDiagcfg.exe
• WindowsSystemMsiesmtp.dll.

It also makes the following changes to the Windows registry:

• HKEY_CLASSES_ROOTcomfileshellopencommand
  It adds diagcfg.exe in front of ""%1"%*".
  
• HKEY_CLASSES_ROOTexefileshellopencommand
  It adds diagcfg.exe in front of ""%1"%*".
  
• HKEY_LOCAL_MACHINESoftwareclassescomfileshellopencommand
  It adds diagcfg.exe in front of ""%1"%*".
  
• HKEY_LOCAL_MACHINESoftwareclassesexefileshellopencommand
  It adds diagcfg.exe in front of ""%1"%*".
  
• HKEY_LOCAL_MACHINESoftwareMicrosoftWindowsCurrentVersionunServices
  It sets diagcfg.exe as the Default key value and adds a key named DiagnosticConfiguration with diagcfg.exe as the value.

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

Remove the changes that the Trojan made to the registry, restart the computer in Safe mode, and then delete the files WindowsSystemDiagcfg.exe and WindowsSystemMsiesmtp.dll. Detailed instructions follow.

NOTE: If the Trojan has executed, you must do the following:

• You must modify the registry before removing Diagcfg.exe because .exe and .com files will look for this file in order to run.
• You must make of copy of Regedit.exe as Regedit.com before you can run the Registry Editor.

Remove the changes that the Trojan made to the registry
Copy Regedit.exe to Regedit.com
Because the Trojan modified the registry so that you cannot run .exe files, you must first make a copy of the Registry Editor as a file with the .com extension and then run that.

1. Do one of the following, depending on which version of Windows you are running:
   • Windows 95/98 users: Click Start, point to Programs, and click MS-DOS Prompt.
   • Windows Me users: Click Start, point to Programs, point to Accessories, and then click MS-DOS Prompt.
   • Windows NT/2000/XP users:
     1. Click Start, and click Run.
     2. Type the following and then press Enter:
        
        command
        
        A DOS window opens.
        
     3. Type the following and then press Enter:
        
        cd winnt
        
     4. Go on to the next step.
        
2. Type the following, and then press Enter:
   
   copy regedit.exe regedit.com
   
3. Type the following, and then press Enter:
   
   start regedit.com
   
   NOTE: The Registry Editor opens in front of the DOS window. After you finish editing the registry and close Registry Editor, close the DOS window.
   
4. Proceed to the following section Edit the registry, and remove keys and changes that the Trojan made only after you have accomplished the previous steps.

Edit the registry, and remove keys and changes that the Trojan made

CAUTION: We strongly recommend 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 and select the following key:
   
   HKEY_CLASSES_ROOTexefileshellopencommand
   
   CAUTION: The HKEY_CLASSES_ROOT key contains many subkey entries that refer to other file extensions. One of these file extensions is .exe. Changing this extension can prevent any files ending with an .exe extension from running. Make sure you browse all the way along this path until you reach the command subkey.
   Do not modify the HKEY_CLASSES_ROOT.exe key.
   Do modify the HKEY_CLASSES_ROOTexefileshellopencommand subkey that is shown in the following figure:
   
   
   <<=== NOTE: This is the key that you need to modify.
   
   
4. Double-click the (Default) value in the right pane.
5. Delete the current value data, and then type: "%1" %* (That is, type the following characters: quote-percent-one-quote-space-percent-asterisk.)
   
   NOTE: On computers that run Windows 9x and Windows NT, the Registry Editor will automatically enclose the value within quotation marks. When you click OK, the (Default) value should look exactly like this: ""%1" %*" On Windows 2000/XP-based systems, the additional quotation marks will not appear. On Windows 2000/XP-based systems, the (Default) value should look exactly like this: "%1" %*
   
6. Make sure you that completely delete all value data in the command key prior to typing the correct data. If you accidentally leave a space at the beginning of the entry, any attempt to run program files will result in the error message, "Windows cannot find .exe." or "Cannot locate C: <path and file name>."
7. Repeat this procedure to for these keys:
   
   HKEY_CLASSES_ROOTcomfileshellopencommand
   HKEY_LOCAL_MACHINESoftwareclassescomfileshellopencommand
   KEY_LOCAL_MACHINESoftwareclassesexefileshellopencommand
   
8. Navigate to the key
   
   HKEY_LOCAL_MACHINESoftwareMicrosoftWindowsCurrentVersionRunServices
   
9. In the right pane, double-click (Default) and delete the contents so that the line is empty.
10. In the left pane, delete the DiagnosticConfiguration subkey.

Restart the computer in Safe mode
All Windows 32-bit operating systems except Windows NT can be restarted in Safe mode. Read the document for your operating system.

• How to start Windows XP in Safe mode
• How to start Windows 2000 in Safe mode
• How to restart Windows 9x or Windows Me in Safe Mode

Remove the Trojan
Use Windows Explorer to delete the files WindowsSystemDiagcfg.exe and WindowsSystemMsiesmtp.dll. Restart the computer, and run a full system scan.