Trojan.Admincash.B

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Discovered: April 25, 2005
Updated: February 13, 2007 12:37:56 PM
Type: Trojan Horse
Systems Affected: Windows


Trojan.Admincash.B is a Trojan horse that infects the Explorer.exe file and downloads adware and dialers.

Antivirus Protection Dates

  • Initial Rapid Release version April 26, 2005
  • Latest Rapid Release version September 28, 2010 revision 054
  • Initial Daily Certified version April 26, 2005
  • Latest Daily Certified version September 28, 2010 revision 036
  • Initial Weekly Certified release date April 27, 2005

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

Writeup By: Rodney Andres

Discovered: April 25, 2005
Updated: February 13, 2007 12:37:56 PM
Type: Trojan Horse
Systems Affected: Windows


When Trojan.Admincash.B is executed, it performs the following actions:

  1. Creates copies of itself as:

    • %Windir%\explorer.new
    • %System%\dllcache\explorer.exe
    • %System%\svhost.exe
    • %System%\[Trojan file name]

      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).
    • %Windir% is a variable that refers to the Windows installation folder. By default, this is C:\Windows (Windows 95/98/Me/XP) or C:\Winnt (Windows NT/2000).

  2. Creates the mutex "bayan", so that only one instance of the Trojan runs at the one time.

  3. Adds the value:

    "System backup" = "%System%\[Trojan file name]"

    to the registry subkeys:

    HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
    HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run

    so that the Trojan runs every time Windows starts.

  4. Adds the following line in the [Windows] section of the Win.ini file, on computers running Windows 95/98/ME:

    run=%System%\svhost.exe

  5. Adds the following line to the Wininit.ini file:

    [Rename]
    %Windir%\explorer.exe=%Windir%\explorer.new

  6. Adds the value:

    "run" = "%System%\svhost.exe"

    to the registry subkey:

    HKEY_CURRENT_USER\Software\Microsoft\Windows NT\CurrentVersion\Windows

    Note: The Trojan adds the value to the above registry subkey on computers running Windows NT/2000/XP only.

  7. Adds the value:

    "DisableSR" = "1"

    to the registry subkeys:

    HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\SystemRestore
    HKEY_CURRENT_USER\Software\Microsoft\Windows NT\CurrentVersion\SystemRestore

    to disable system restore.

  8. Adds the values:

    "NoAutoUpdate" = "1"
    "AUOptions" = "1"

    to the registry subkeys:

    HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows\WindowsUpdate\AU
    HKEY_CURRENT_USER\Software\Policies\Microsoft\Windows\WindowsUpdate\AU

    to disable automatic Windows Updates.

  9. Adds the values:

    "FirewallDisableNotify" = "1"
    "UpdatesDisableNotify" = "1"
    "AntiVirusDisableNotify" = "1"

    to the registry subkeys:

    HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Security Center
    HKEY_CURRENT_USER\Software\Microsoft\Security Center

    to disable notification of firewall, antivirus, and update status through the Windows Security Center.

  10. Adds the value:

    "SelfLimit" = "1"

    to the registry subkeys:

    HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Internet Explorer\Main
    HKEY_CURRENT_USER\SOFTWARE\Microsoft\Internet Explorer\Main

    as an infection marker.

  11. Infects the file %Windir%\explorer.exe.

  12. Downloads several adware and dialer programs from the advadmin.biz domain.

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: Rodney Andres

Discovered: April 25, 2005
Updated: February 13, 2007 12:37:56 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. Restore Explorer.exe
  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.Admincash.B.
  5. Delete any values added to the registry.
  6. Restore the Windows Security Center
  7. Edit the Win.ini and Wininit.ini files
For specific details on each of these steps, read the following instructions.

1. To restore Explorer.exe
Important : This must be done before you restart your computer, otherwise Windows may not restart properly.
  1. Click Start > Programs > Accessories > Command Prompt
  2. Type sfc /scannow
  3. Insert the Windows installation CD when prompted.
2. 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).

3. 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.


4. 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 Trojan.Admincash.B, 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.

    Warning messages may be displayed when the computer is restarted, as the threat has not been fully removed at this point. Please ignore these messages and just click OK. These messages will not appear when the computer is restarted after the removal instructions have been fully completed. The messages displayed may be similar to the following:

    Title: [File path]
    Message body: Windows cannot find [file name]. Make sure you typed the name correctly, and then try again. To search for a file, click the Start button, and then click Search.

5. 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 the subkeys:

    HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
    HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run

  5. In the right pane, delete the value:

    "System backup" = "%System%\[Trojan file name]"

  6. Navigate to the subkey:

    HKEY_CURRENT_USER\Software\Microsoft\Windows NT\CurrentVersion\Windows

  7. In the right pane, delete the value:

    "run" = "%System%\svhost.exe"

  8. Navigate to the subkeys:

    HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Internet Explorer\Main
    HKEY_CURRENT_USER\SOFTWARE\Microsoft\Internet Explorer\Main

  9. In the right pane, delete the value:

    "SelfLimit" = "1"

  10. Exit the Registry Editor.

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. Edit the Win.ini and Wininit.ini files
If you are running Windows 95/98/Me, follow these steps:
  1. Click Start > Run.
  2. Type the following:

    edit %Windir%\win.ini

    and then click OK.

    Note: %Windir% is a variable that refers to the Windows installation folder. By default, this is C:\Windows or C:\Winnt.

  3. In the [windows] section of the file, look for a line similar to:

    run=%System%\svhost.exe

    Note: %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).

  4. If this line exists, delete everything to the right of run=
  5. Click File > Save.
  6. Click File > Exit.
  7. Click Start > Run.
  8. Type the following:

    edit c:\windows\wininit.ini

    and then click OK.

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

  9. In the [windows] section of the file, look for a line similar to:

    [Rename]
    %Windir%\explorer.exe=%Windir%\explorer.new

    Note: %Windir% is a variable that refers to the Windows installation folder. By default, this is C:\Windows or C:\Winnt.

  10. If this line exists, delete it.
  11. Click File > Save.
  12. Click File > Exit.


Writeup By: Rodney Andres