W32.Tendoolf

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Discovered: May 01, 2002
Updated: February 13, 2007 11:59:57 AM
Also Known As: Backdoor.SubSeven, W32/Floodnet@MM, Win32/Cute.Worm, WORM_TENDOOLF.A
Type: Trojan Horse
Systems Affected: Windows



W32.Tendoolf is a variant of Backdoor.Subseven , which appears to be able to spread through email. The email message has the following characteristics:

Subject: Thoughts...
Message: I just found this program, and, i dont know why... but it reminded me of you. check it out.
Attachment: Cute.exe

The mailing routine has not been successfully reproduced in a laboratory environment.



Definitions dated prior to May 2, 2002, may detect this as Backdoor.SubSeven.

Antivirus Protection Dates

  • Initial Rapid Release version May 02, 2002
  • Latest Rapid Release version September 28, 2010 revision 054
  • Initial Daily Certified version May 02, 2002
  • Latest Daily Certified version September 28, 2010 revision 036
  • Initial Weekly Certified release date May 08, 2002

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

Writeup By: Douglas Knowles

Discovered: May 01, 2002
Updated: February 13, 2007 11:59:57 AM
Also Known As: Backdoor.SubSeven, W32/Floodnet@MM, Win32/Cute.Worm, WORM_TENDOOLF.A
Type: Trojan Horse
Systems Affected: Windows


When W32.Tendoolf is executed, it does the following:

It copies itself to C:\Windows\Kernel32.exe.

It adds the value

Windows      C:\WINDOWS\KERNEL32.EXE

to the following registry keys:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\
CurrentVersion\Run

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\
CurrentVersion\RunServices

It then changes a line in the System.ini file from

shell=Explorer.exe

to

shell=explorer.exe C:\WINDOWS\KERNEL32.EXE

It also changes a line in the Win.ini file from

load=

to

load=C:\WINDOWS\KERNEL32.EXE

W32.Tendoolf appears to be coded to have the ability to spread through email. The email message has the following characteristics:

Subject: Thoughts...
Message: I just found this program, and, i dont know why... but it reminded me of you. check it out.
Attachment: Cute.exe

The mailing routine has not been successfully reproduced in a laboratory environment.

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: Douglas Knowles

Discovered: May 01, 2002
Updated: February 13, 2007 11:59:57 AM
Also Known As: Backdoor.SubSeven, W32/Floodnet@MM, Win32/Cute.Worm, WORM_TENDOOLF.A
Type: Trojan Horse
Systems Affected: Windows


Delete files that are detected as W32.Tendoolf, remove the values that it added to the registry, and (Windows 95/98/Me only) remove the text that it added to the two Windows startup files.

To delete files that are detected as W32.Tendoolf:

  1. Obtain the most recent virus definitions. There are two ways to do this:
    • Run LiveUpdate. LiveUpdate is the easiest way to obtain virus definitions. These virus definitions have undergone full quality assurance testing by Symantec Security Response and are posted to the LiveUpdate servers one time each week (usually Wednesdays) unless there is a major virus outbreak. To determine whether definitions for this threat are available by LiveUpdate, look at the Virus Definitions (LiveUpdate) line at the top of this write-up.
    • Download the definitions using the Intelligent Updater. Intelligent Updater virus definitions have undergone full quality assurance testing by Symantec Security Response. They are posted on U.S. business days (Monday through Friday). They must be downloaded from the Symantec Security Response Web site and installed manually. To determine whether definitions for this threat are available by the Intelligent Updater, look at the Virus Definitions (Intelligent Updater) line at the top of this write-up.

      Intelligent Updater virus definitions are available here. For detailed instructions on how to download and install the Intelligent Updater virus definitions from the Symantec Security Response Web site, click here.
  2. Start Norton AntiVirus (NAV), and make sure that NAV is configured to scan all files. For instructions on how to do this, read the document How to configure Norton AntiVirus to scan all files.
  3. Run a full system scan.
  4. Delete all files that are detected as W32.Tendoolf.

To remove the values that W32.Tendoolf added to the registry:

CAUTION : Symantec strongly recommends that you back up the registry before you make any changes to it. Incorrect changes to the registry can result in permanent data loss or corrupted files. Modify only the keys that are specified. Read the document How to make a backup of the Windows registry for instructions.
  1. Click Start, and click Run. The Run dialog box appears.
  2. Type regedit and then click OK. The Registry Editor opens.
  3. Navigate to each of the following keys:

    HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\
    CurrentVersion\Run

    HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\
    CurrentVersion\RunServices
  4. In the right pane, delete the following value:

    Windows      C:\WINDOWS\KERNEL32.EXE
  5. Click Registry, and click Exit.

To remove the text that W32.Tendoolf added to the Windows startup files:

NOTE: This is only necessary on Windows 95/98/Me.
  1. Click Start, and click Run.
  2. Type the following, and then click OK.

    edit c:\windows\win.ini

    The MS-DOS Editor opens.

    NOTE: If Windows is installed in a different location, make the appropriate path substitution.
  3. In the [windows] section of the file, look for an entry similar to the following:

    load=C:\WINDOWS\KERNEL32.EXE
  4. Select the entire line. Be sure that you have not selected any other text, and then press Delete.
  5. Click File, and click Save.
  6. Click File, and click Exit.
  7. Click Start, and click Run.
  8. Type the following, and then click OK.

    edit c:\windows\system.ini

    The MS-DOS Editor opens.

    NOTE: If Windows is installed in a different location, make the appropriate path substitution.
  9. In the [boot] section, locate the following line:

    shell=explorer.exe C:\WINDOWS\KERNEL32.EXE
  10. Delete the text to the right of shell=explorer.exe so that the line consists of only:

    shell=explorer.exe
  11. Click File, and click Save.
  12. Click File, and click Exit.


Writeup By: Douglas Knowles