Backdoor.Apdoor

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Discovered: June 04, 2003
Updated: February 13, 2007 12:02:25 PM
Also Known As: CoreFlood [McAfee], Backdoor.Apdoor.b [KAV]
Type: Trojan Horse
Systems Affected: Windows


Backdoor.Apdoor is a Backdoor Trojan Horse that is similar to Backdoor.Coreflood . It allows unauthorized remote access to the system on which it is running and supports the commands to modify the registry settings, transfer files, and start or end processes.

A sign of possible infection is the existence of two files in the %System% folder. These files will be in the following format:

  • ABCDEFG.exe (28160 bytes)
  • ABCDEFG.dll (69632 bytes)
The actual filenames that the Trojan uses are random.


Antivirus Protection Dates

  • Initial Rapid Release version June 04, 2003
  • Latest Rapid Release version March 03, 2008 revision 035
  • Initial Daily Certified version June 04, 2003
  • Latest Daily Certified version March 03, 2008 revision 037
  • Initial Weekly Certified release date June 04, 2003

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

Writeup By: Heather Shannon

Discovered: June 04, 2003
Updated: February 13, 2007 12:02:25 PM
Also Known As: CoreFlood [McAfee], Backdoor.Apdoor.b [KAV]
Type: Trojan Horse
Systems Affected: Windows


The Trojan consists of two parts:

  • A .exe file, which is the loader.
  • A .dll file, which contains the primary code.

When Backdoor.Apdoor runs, it does the following:
  1. Extracts the .dll file from itself to the default temporary folder.

  2. Copies itself and the .dll file to the %System% folder. The filenames consist of seven random characters.

    NOTE: %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).

    Then, the .exe file calls a function within the .dll file to begin executing the main code. The main code hooks the Explorer.exe process in such a way that all its actions run under the process context of Explorer.exe.

  3. When the main code is run, the Trojan adds the value:

    "<file name>"="%system%\<file name>.exe"

    to the registry key:

    HKEY_LOCAL_MACHINE/SOFTWARE/Microsoft/Windows/CurrentVersion/Run

    so that the Trojan runs each time that you start Windows. The Trojan monitors this registry key and may add it again if it is modified or removed.


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: June 04, 2003
Updated: February 13, 2007 12:02:25 PM
Also Known As: CoreFlood [McAfee], Backdoor.Apdoor.b [KAV]
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. Disable System Restore (Windows Me/XP).
  2. Update the virus definitions.
  3. Restart the computer in Safe mode (Windows 95/98/Me/2000/XP) or VGA mode (Windows NT 4).
  4. Run a full system scan and delete all the files detected as Backdoor.Apdoor.
  5. Reverse the changes that the Trojan made to the registry.
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:
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. Restarting the computer in Safe mode or VGA mode
  • For Windows 95, 98, Me, 2000, or XP users, restart the computer in Safe mode. For instructions on restarting in Safe mode, refer to the document, "How to start the computer in Safe Mode."
  • For Windows NT 4 users, restart the computer in VGA mode.
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 Backdoor.Apdoor, write down the filenames, and then click Delete.

5. Reversing the changes made to 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, delete the value:

    <file name> %system%\<file name>.exe

    NOTE: The filename should match the files that were deleted in step 4.

  5. Exit the Registry Editor.


Writeup By: Heather Shannon