Symantec Security Response

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Backdoor.Fivsec

Risk Level 1: Very Low

Discovered: March 30, 2005
Updated: February 13, 2007 12:36:05 PM
Type: Trojan Horse
Systems Affected: Windows 2000, Windows 95, Windows 98, Windows Me, Windows NT, Windows Server 2003, Windows XP

SUMMARY


Backdoor.Fivsec is a Trojan horse that opens a back door on a randomly chosen TCP port.

Protection

  • Initial Rapid Release version March 31, 2005
  • Latest Rapid Release version March 31, 2009 revision 036
  • Initial Daily Certified version March 31, 2005
  • Latest Daily Certified version April 15, 2009 revision 048
  • Initial Weekly Certified release date March 31, 2005

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

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

TECHNICAL DETAILS


When Backdoor.Fivsec is executed, it performs the following actions:
  1. Drops the following files:

    • %Temp%\pi.sys
    • %System%\thun.dll
    • %System%\thun32.dll

      Notes:
    • %System% is a variable that refers to the System folder. By default this is C:\Windows\System (Windows 95/98/Me), C:\Winnt\System32 (Windows NT/2000), or C:\Windows\System32 (Windows XP).
    • %Temp% is a variable that refers to the Windows temporary folder. By default, this is C:\Windows\TEMP (Windows 95/98/Me/XP) or C:\WINNT\Temp (Windows NT/2000).

  2. Runs thun32.dll as a thread to one of the following processes so that it is executed every time Windows starts:

    • rundll32.exe
    • explorer.exe

  3. Creates the following registry entries:

    HKEY_CURRENT_USER\Software\Classes\CLSID
    \{0656A137-B161-CADD-9777-E37A75727E78}
    HKEY_CLASSES_ROOT\CLSID\{0656A137-B161-CADD-9777-E37A75727E78}
    HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Services\wscsvc
    HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\wscsvc
    HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer
    \SharedTaskScheduler\"{0656A137-B161-CADD-9777-E37A75727E78}"

  4. Adds the values:

    "dll" = "00, 00, 00, 00"
    "id" = "124517651736"
    "rpt" = "E8, 22, 00, 00"

    to the registry subkey:

    HKEY_CURRENT_USER\Software\Microsoft\InternetExplorer\Security

    to modify the security settings in Windows and in Internet Explorer.

  5. Adds the values:

    "1001" = "01, 00, 00, 00"
    "1004" = "01, 00, 00, 00"
    "1200" = "00, 00, 00, 00"
    "1809" = "03, 00, 00, 00"

    to the registry subkeys:

    HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion
    \InternetSettings\Zones
    HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion
    \InternetSettings\Zones

    to modify the security settings in Windows and in Internet Explorer.

  6. Adds the values:

    "AntiVirusDisableNotify" = "01, 00, 00, 00"
    "AntiVirusOverride" = "01, 00, 00, 00"
    "FirewallDisableNotify" = "01, 00, 00, 00"
    "FirewallOverride" = "01, 00, 00, 00"
    "UpdatesDisableNotify" = "01, 00, 00, 00"

    to the registry subkey:

    HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\SecurityCenter

    to modify the security settings in Windows and in Internet Explorer.

  7. Adds the value:

    "EnableFirewall" = "00, 00, 00, 00"

    to the registry subkeys:

    HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\WindowsFirewall
    \DomainProfile
    HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\WindowsFirewall
    \StandardProfile


    to modify the security settings in Windows and in Internet Explorer.

  8. Adds the value:

    "DoNotAllowXPSP2" = "01, 00, 00, 00"

    to the registry subkey:

    HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows\WindowsUpdate

    to modify the security settings in Windows and in Internet Explorer.
  9. Deletes the following service:

    Service name: Internet Connection Firewall (ICF) / Internet Connection Sharing (ICS)

  10. Connects to the following domains and notifies them of the IP address of the compromised computer:

    • 5sec.biz
    • 5sec.org

  11. Opens a back door on a randomly chosen TCP port and waits for commands from the author.


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.

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 the files detected as Backdoor.Fivsec.
    4. Delete any values added to the registry.
    5. Reenable the SharedAccess service.
    6. Restore the Windows Security Center.
    7. Restore security settings in Internet Explorer.
    For specific details on each of these steps, read the following instructions.

    1. To disable 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, reenable 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).

    2. To update 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 document: Virus Definitions (LiveUpdate).
    • Downloading the definitions using the Intelligent Updater: The Intelligent Updater virus definitions are posted daily. 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 document: Virus Definitions (Intelligent Updater).

      The latest Intelligent Updater virus definitions can be obtained here: Intelligent Updater virus definitions. For detailed instructions read the document: How to update virus definition files using the Intelligent Updater.


    3. To scan for and delete 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 Backdoor.Fivsec, click Delete.

      Note:       If your Symantec antivirus product reports that it cannot delete an infected file, Windows may be using the file. To fix this, run the scan in Safe mode. For instructions, read the document: How to start the computer in Safe Mode. Once you have restarted in Safe mode, run the scan again.

      After the files are deleted, restart the computer in Normal mode and proceed with section 4.

    4. To delete the value from the registry
    Important: 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 subkeys only. For instructions refer to the document: How to make a backup of the Windows registry.
    1. Click Start > Run.
    2. Type regedit
    3. Click OK.

    4. Navigate to and delete the following subkeys:

      HKEY_CURRENT_USER\Software\Classes\CLSID
      \{0656A137-B161-CADD-9777-E37A75727E78}
      HKEY_CLASSES_ROOT\CLSID\{0656A137-B161-CADD-9777-E37A75727E78}
      HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Services\wscsvc
      HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\wscsvc
      HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer
      \SharedTaskScheduler\"{0656A137-B161-CADD-9777-E37A75727E78}"
      HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows\WindowsUpdate
      \"DoNotAllowXPSP2"
      HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\SecurityCenter
      \"UpdatesDisableNotify"

    5. Exit the Registry Editor.
    5. To reenable the SharedAccess service (Windows 2000/XP only)
    The SharedAccess service is responsible for maintaining Internet Connection Sharing and the Windows Firewall/Internet Connection Firewall applications in Windows. (The presence and names of these applications vary depending on the operating system and service pack you are using.) To protect your computer and maintain network functionality, re-enable this service if you are using any of these programs.


    Windows XP Service Pack 2
    If you are running Windows XP with Service Pack 2 and are using the Windows Firewall, the operating system will alert you when the SharedAccess service is stopped, by displaying an alert balloon saying that your Firewall status is unknown. Perform the following steps to ensure that the Windows Firewall is re-enabled:
    1. Click Start > Control Panel.
    2. Double-click the Security Center.
    3. Ensure that the Firewall security essential is marked ON.

      Note: If the Firewall security essential is marked on, your Windows Firewall is on and you do not need to continue with these steps.

      If the Firewall security essential is not marked on, click the "Recommendations" button.

    4. Under "Recommendations," click Enable Now. A window appears telling you that the Windows Firewall was successfully turned on.
    5. Click Close, and then click OK.
    6. Close the Security Center.


    Windows 2000 or Windows XP Service Pack 1 or earlier
    Complete the following steps to re-enable the SharedAccess service:
    1. Click Start > Run.
    2. Type services.msc

      Then click OK.

    3. Do one of the following:
      • Windows 2000: Under the Name column, locate the "Internet Connection Sharing (ICS)" service and double-click it.
      • Windows XP: Under the Named column, locate the "Internet Connection Firewall (ICF) / Internet Connection Sharing (ICS)" service and double-click it.

    4. Under "Startup Type:", select "Automatic" from the drop-down menu.
    5. Under "Service Status:", click the Start button.
    6. Once the service has completed starting, click OK.
    7. Close the Services window.


    6. To restore the Windows Security Center
    This threat attempts to disable the features in the Windows Security Center, available in Windows XP Service Pack 2. If you are running Windows XP Service Pack 2 and would like to restore the full functionality of the Windows Security Center, please complete the following steps:

    Important: If your computer is connected to a domain, you may not be able to adjust these settings. If so, contact your network administrator for more information.
    1. Click Start > Control Panel.
    2. Double-click the Security Center.
    3. In the right pane, click Windows Firewall. The Windows Firewall appears.
    4. Select On.
    5. Click OK to close the Windows Firewall.
    6. In the left pane of the Security Center, select Change the way Security Center alerts me.
    7. Click Alert Settings.
    8. Select Alert Settings, Firewall, and Virus Protection.
    9. Click OK
    10. Click Automatic Updates.
    11. Select Automatic.
    12. Click OK.
    13. Exit the Security Center.

    7. To restore security settings in Internet Explorer
    1. Open Internet Explorer
    2. Go to the Tools menu and click on Internet Options
    3. Click on the security tab
    4. For each Zone, configure the security settings appropriately or click on Default Level to change settings to default.


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