Threat Explorer

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VBS.Tam.A

VBS.Tam.A

Updated:
13 February 2007
Also Known As:
VBS.Out, VBS/Out@M

VBS.Tam.A is a worm that is only able to run on French Windows operating systems. The worm uses a known security bug in Microsoft Outlook Express called Scriplet . Typelib. Wscript.KakWorm was the first worm to use this security hole.

Microsoft has since patched this security hole. The patch is available on the Microsoft Web site . If you have a patched version of Outlook Express, the worm will not work.

Antivirus Protection Dates

  • Initial Rapid Release version 17 October 2000
  • Latest Rapid Release version 28 September 2010 revision 054
  • Initial Daily Certified version 17 October 2000
  • Latest Daily Certified version 28 September 2010 revision 036
  • Initial Weekly Certified release date pending
Click here for a more detailed description of Rapid Release and Daily Certified virus definitions.

VBS.Tam.A uses a known Microsoft Outlook Express security hole, Scriptlet . Typelib, so that a viral file is created on the system without having to run an attachment. Simply reading or previewing an email message with the worm attached causes the worm to be placed on the system.

Upon execution, the worm inserts a copy of itself into the Windows StartUp folder. However, this only works if the operating system is French. The worm creates a file named Tam.hta.

Microsoft has patched the Scriplet . Typelib security hole. The patch is available on the Microsoft Web site . If you have a patched version of Outlook Express, the worm will not work. Instead, if an infected email message is viewed, a Microsoft ActiveX warning dialog box is displayed.

Since the worm drops the file into the StartUp folder, the system must be restarted before the file is executed. Once executed, the worm creates the C:\Windows\Out.html and C:\Windows\Out.hta files.

It also modifies the following registry key in order to add its own signature file, which is the infected Out.html file:

HKEY_CURRENT_USER/Identities//Software/Microsoft/Outlook/Express/5.0/signatures

This causes all outgoing mail to be appended by the worm.

In addition, it adds the following registry key to cause the worm to be executed each time the computer is restarted:

HKEY_LOCAL_MACHINE/Software/Microsoft/Windows/CurrentVersion/Run/OutGoingCtrl

On the August 30, the worm displays a dialog box on infected systems, containing the following text:
    Bon Anniversaire Lac
    Un ami...,
    Translated to English:
    Happy birthday Lac
    a friend...

After clicking the OK button five times, the worm may or may not display a dialog box containing the following text:

    KOI??? Ca t'interresse pas? Tu n'es pas digne du monde informatique. BYE-BYE
    Translated to English:
    KOI??? it doesn't interest you? you're not worthy of the IT world. BYE-BYE

Whether the message is displayed and the computer restarted depends on a value that is calculated when the OK button in the dialog box is pressed. If this message is not displayed, the worm displays the following text:
    Ok, chante HappyBirthday tout ira bien!!!
    Translated to English:
    Ok, sing Happy birthday and everything will be just fine.
    The computer is not be restarted.

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.

Delete all infections, and install the Microsoft security update .

Writeup By: Neal Hindocha