Trojan.Gutta

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Discovered: February 09, 2004
Updated: February 13, 2007 12:17:11 PM
Type: Trojan Horse
Systems Affected: Windows


Trojan.Gutta is a Trojan horse that disables access to .exe files.

Antivirus Protection Dates

  • Initial Rapid Release version February 10, 2004
  • Latest Rapid Release version August 20, 2008 revision 017
  • Initial Daily Certified version February 10, 2004
  • Latest Daily Certified version August 20, 2008 revision 016
  • Initial Weekly Certified release date February 11, 2004

Click here for a more detailed description of Rapid Release and Daily Certified virus definitions.

Writeup By: Maryl Magee

Discovered: February 09, 2004
Updated: February 13, 2007 12:17:11 PM
Type: Trojan Horse
Systems Affected: Windows


Trojan.Gutta disables access to files with the .exe extension. When this Trojan runs, it performs the following actions:

  1. Copies itself as C:\Windows\CSRSS.exe. This path is hard-coded and does not depend on system variables.

  2. Creates the value:

    "rundll32" = "windows\csrss.exe"

    in the registry key:

    HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Run

    so that the Trojan attempts to start when you start Windows.

  3. Modifies the value of:

    (Default)

    in the registry key:

    HKEY_CLASSES_ROOT\exefile\shell\open\command

    by adding:

    hahafool

    to the Value data. As a result, when you try to run a .exe file, it will not open. For example, if you try to run Notepad.exe after the modification is made, instead of looking for Notepad.exe, it looks for Notepad.exehahafool.

This Trojan horse does not have backdoor or worm functionality. Because it modifies access to .exe files, it cannot run when Windows is restarted, but will generate an error message.

Recommendations

Symantec Security Response encourages all users and administrators to adhere to the following basic security "best practices":

  • Use a firewall to block all incoming connections from the Internet to services that should not be publicly available. By default, you should deny all incoming connections and only allow services you explicitly want to offer to the outside world.
  • 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.
  • Ensure that programs and users of the computer use the lowest level of privileges necessary to complete a task. When prompted for a root or UAC password, ensure that the program asking for administration-level access is a legitimate application.
  • Disable AutoPlay to prevent the automatic launching of executable files on network and removable drives, and disconnect the drives when not required. If write access is not required, enable read-only mode if the option is available.
  • Turn off file sharing if not needed. If file sharing is required, use ACLs and password protection to limit access. Disable anonymous access to shared folders. Grant access only to user accounts with strong passwords to folders that must be shared.
  • Turn off and remove unnecessary services. By default, many operating systems install auxiliary services that are not critical. These services are avenues of attack. If they are removed, threats have less avenues of attack.
  • If a 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.
  • Configure your email server to block or remove email that contains file attachments that are commonly used to spread threats, such as .vbs, .bat, .exe, .pif and .scr files.
  • Isolate compromised computers quickly to prevent threats from spreading further. 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.
  • If Bluetooth is not required for mobile devices, it should be turned off. If you require its use, ensure that the device's visibility is set to "Hidden" so that it cannot be scanned by other Bluetooth devices. If device pairing must be used, ensure that all devices are set to "Unauthorized", requiring authorization for each connection request. Do not accept applications that are unsigned or sent from unknown sources.
  • For further information on the terms used in this document, please refer to the Security Response glossary.

Writeup By: Maryl Magee

Discovered: February 09, 2004
Updated: February 13, 2007 12:17:11 PM
Type: Trojan Horse
Systems Affected: Windows


The following instructions pertain to all current and recent Symantec antivirus products, including the Symantec AntiVirus and Norton AntiVirus product lines.

  1. Reverse the changes that were made to the registry.
  2. Disable System Restore (Windows Me/XP).
  3. Update the virus definitions.
  4. Run a full system scan and delete all the files detected as Trojan.Gutta.
For specific details on each of these steps, read the following instructions.

1. Reversing the changes that were made to the registry.
Because the worm modified the registry so that you cannot run any .exe files, first make a copy of the Registry Editor as a file with the .com extension, and then run that file.
  1. Do one of the following, depending on the version of Windows you are running:
    • Windows 95/98 users:
      1. Click Start.
      2. Point to Programs.
      3. Click the MS-DOS Prompt. (A DOS window opens at the C:\Windows prompt.) Proceed to step B of this section.

    • Windows Me users:
      1. Click Start.
      2. Point to Programs.
      3. Point to Accessories.
      4. Click the MS-DOS Prompt. (A DOS window opens at the C:\Windows prompt.) Proceed to step B of this section.

    • Windows NT/2000 users:
      1. Click Start, and then click Run.
      2. Type command, and then press Enter. (A DOS window opens.)
      3. Type cd \winnt, and then press Enter.
      4. Go to step B of this section.

    • Windows XP users:
      1. Click Start, and then click Run.
      2. Type command, and then press Enter. (A DOS window opens.)
      3. Type the following:

        cd\
        cd \windows

        Press Enter after typing each one.

      4. Proceed to step B of this section.

  2. Type copy regedit.exe regedit.com

    and then press Enter.

  3. Type start regedit.com

    and then press Enter. (The Registry Editor opens in front of the DOS window.)

    After you finish editing the registry, exit the Registry Editor, and then exit the DOS window as well.

  4. Before continuing, 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. For instructions, read the document, "How to make a backup of the Windows registry."

  5. Navigate to and select the key:

    HKEY_CLASSES_ROOT\exefile\shell\open\command

    NOTE: 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 a .exe extension from running. Make sure that you completely browse through this path until you reach the \command subkey.

    Modify the HKEY_CLASSES_ROOT\exefile\shell\open\command subkey, shown in the following figure:

    <<=== NOTE: Modify this key.

  6. In the right pane, double-click the (Default) value.
  7. Click in the Value data field to the right of the text so that the current value data is no longer selected in blue.
  8. Backspace to delete the characters:

    hahafool

    Make sure that you do not delete the text:

    "%1" %*

  9. Click OK.

  10. Navigate to the key:

    HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run

  11. In the right pane, delete the value:

    "rundll32"="C:\Windows\CSRSS.exe"

  12. Exit the Registry Editor.

2. 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:
Note: When you are completely finished with the removal procedure and are satisfied that the threat has been removed, re-enable System Restore by following the instructions in the aforementioned documents.

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.

3. 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.

4. 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.
  2. Run a full system scan.
  3. If any files are detected as infected with Trojan.Gutta, click Delete.


Writeup By: Maryl Magee