Backdoor.Grobodor

SUMMARY

Backdoor.Grobodor is a back door Trojan horse that gives its creator unauthorized access to your computer. It opens port 31332 by default. Backdoor.Grobodor is written in the Delphi programming language and is packed with UPX.

Protection

• Virus Definitions (LiveUpdate™ Weekly) June 11, 2003
• Virus Definitions (Intelligent Updater) June 9, 2003

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: Low

Distribution

• Distribution Level: Low
• Ports: TCP port 31332.

TECHNICAL DETAILS

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

1. By default, copies itself as %Windir%MSDRV32.exe.
   
   The directory can be configured to be %System%, %Temp% or %Windir% and the file name is also configurable.
   
   

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   Notes:
   • %Windir% is a variable. The Trojan locates the Windows installation folder (by default, this is C:Windows or C:Winnt) and may copy itself to that location.
   • %System% is a variable. The Trojan locates the System folder and may copy itself to that location. By default, this is C:WindowsSystem (Windows 95/98/Me), C:WinntSystem32 (Windows NT/2000), or C:WindowsSystem32 (Windows XP).
   • %Temp% is a variable. The Trojan locates the temporary folder and may copy itself to that location. By default, this is C:WindowsTEMP (Windows 95/98/Me/XP) or C:WINNTTemp (Windows NT/2000).

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1. By default, adds the value:
   
   "System drivers"="[filename from step 1]".
   
   to the following registry keys:
   
   HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindowsCurrentVersionRun
   HKEY_CURRENT_USERSOFTWAREMicrosoftWindowsCurrentVersionRun
   
   The value name is configurable.
   
2. On Windows 95/98/Me-based computers, the Trojan modifies the run= lines of the Win.ini file to the following:
   
   run=[filename from step 1]
   
   
3. By default, opens port 31332/TCP.
   
   This port is configurable.

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. Run a full system scan and delete all files that are detected as Backdoor.Grobodor.
4. Delete the values that were added to the registry.
5. Delete the line that was added to the Win.ini file (Windows 95/98/Me).
   

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

1. Disabling 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"

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. 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.

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.Grobodor, write down the path and file names, and then click Delete..

4. Deleting the value from 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 each of these keys:
   
   HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindowsCurrentVersionRun
   HKEY_CURRENT_USERSOFTWAREMicrosoftWindowsCurrentVersionRun
   
   
4. Refer to the list of infected files that you created while following the instructions in the previous section. In the right pane, look at the entries in the Name and Data columns. If you find an entry that refers to a file that was detected as infected, select the entry, press Delete, and then click Yes to confirm.
   
   
5. Exit the Registry Editor.

5. Deleting the changes to the Win.ini file

If you are running Windows 95/98/Me, follow these steps:

1. The function you perform depends on your version of Windows:
   • Windows 95/98
     Go to step b.
   • Windows Me
     If you are running Windows Me, the Windows Me file-protection process may have made a backup copy of the Win.ini file that you need to edit. If this backup copy exists, it will be in the C:WindowsRecent folder. Symantec recommends that you delete this file before continuing with the steps in this section. To do this:
     1. Start Windows Explorer.
     2. Browse to and select the C:WindowsRecent folder.
     3. In the right pane, select the Win.ini file and delete it. The Win.ini file will be regenerated when you save your changes to it in step c.
        
        
2. Click Start, and then click Run.
   
   
3. Type the following, and then click OK:
   
   edit c:windowswin.ini
   
   The MS-DOS Editor opens.
   
   

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   Note: If Windows is installed in a different location, make the appropriate path substitution.
   

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   WARNING: The following steps instruct you to remove text from the load= and run= lines of the Win.ini file. If you are using older programs, they may be loading at startup from one of these lines. The Trojan can add lines, such as load=c:windows emppkg2350.exe or run=hpfsched <blank spaces> msrexe.exe. (In this example, hpfsched is a legitimate program, but msrexe.exe is part of the Trojan.)
   

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   If you are sure that the text contained in these lines is for programs that you normally use, then we suggest that you do not remove it. If you are not sure, but the text does not refer to the file names you wrote down earlier, then you can prevent the lines from loading by placing a semicolon in the first character position of the line.
   
   For example:
   
   run=MSDRV32.exe