Backdoor.Delf.Family

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Discovered: May 05, 2003
Updated: February 13, 2007 12:00:50 PM
Type: Trojan Horse
Systems Affected: Windows


Backdoor.Delf.Family is a family of Backdoor Trojan Horse programs. Members of this family typically capture private data, such as logging keystrokes.

Antivirus Protection Dates

  • Initial Rapid Release version May 05, 2003
  • Latest Rapid Release version September 28, 2010 revision 054
  • Initial Daily Certified version May 05, 2003
  • Latest Daily Certified version September 28, 2010 revision 036
  • Initial Weekly Certified release date May 07, 2003

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

Writeup By: Heather Shannon

Discovered: May 05, 2003
Updated: February 13, 2007 12:00:50 PM
Type: Trojan Horse
Systems Affected: Windows



When a Backdoor.Delf.Family Trojan is executed, it will typically:

  • Open a network connection.
  • End processes, such as those belonging to antivirus products.
  • Copy itself to another file, sometimes deleting the original.
  • Modify the registry so that the Trojan is executed when you start Windows.

The following descriptions discuss several variants, which are detected as Backdoor.Delf.Family, as well as their characteristics:

Variant 1
  • Listens on port 2444.
  • Copies itself to %System%\SysService.exe:
  • Creates the value:

    "SysService"="%System%\SysService.exe"

    in the registry key:

    HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run.

Variant 2
  • Listens on port 27,378.
  • Copies itself to %Windir%\hap1\win32.com. (It first creates the folder %Windir%\hap1.)
  • Creates the value:

    "Common Startup"="%Windir%\hap1"

    in the registry key:

    HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\explorer\User Shell Folders
Variant 3
  • Listens on port 2,189.
  • Does not copy itself, but runs from its original location with the filename interdll.exe.
  • Creates the value:

    "Interdll"="<the path to the file>\interdll.exe"

    in the registry key:

    HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run.
Variant 4
  • Listens on port 23.
  • Copies itself to %Windir%\msgsrv16.exe.
  • Creates the value:

    "Msgsrv16"="%Windir%\Msgsrv16.exe"

    in the registry key:

    HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run.

Other variants will have different configurations.

NOTES:
  • %Windir% is a variable: The Trojan locates the Windows installation folder (by default, this is C:\Windows or C:\Winnt) and copies itself to that location.
  • %System% is a variable: The Trojan locates the System folder and copies itself to that location. By default, this is C:\Windows\System (Windows 95/98/Me), C:\Winnt\System32 (Windows NT/2000), or C:\Windows\System32 (Windows XP).


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: Heather Shannon

Discovered: May 05, 2003
Updated: February 13, 2007 12:00:50 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. Update the virus definitions.
  2. Run a full system scan and delete all the files detected as Backdoor.Delf.Family, or a specific variant, such as Backdoor.Delf.X.
  3. Delete the value that was added to the registry.
For specific details on each of these steps, 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 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.

2. 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 Backdoor.Delf.Family, or similar names, note the filename for use when checking the registry, and then click Delete.

3. Deleting the value from the registry

CAUTION : 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.
  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 the key:

    HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
  4. In the right pane, look for a value that matches the infected files, which were deleted in step 2. For example, if the file "SysService.exe" was deleted, the registry value might be:

    "(anything)" = "C:\Windows\System\SysService.exe"

    If no such value exists, the Trojan might have startup information in another registry key. Look for it in the following registry keys:

    HKEY_CURRENT_USER\SOFTWARE\Microsoft\Windows\CurrentVersion\Run HKEY_CURRENT_USER\SOFTWARE\Microsoft\Windows\CurrentVersion\RunOnce HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run  HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\RunOnce HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\RunServices HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\RunServicesOnce
  5. Exit the registry editor.


Writeup By: Heather Shannon