F-Secure Virus Descriptions : Cardown.B

Summary

Cardown.B is a Java applet based trojan that downloads and installs Startpage.Y trojan on the system.

Cardown activates when user views a web page or HTML email that contains reference to the trojan file.

Cardown does not replicate and does not infect the host system, the only operations it does is to modify Interner Explorer start page and download and install Startpage.Y trojan component.

Disinfection

Disinfection Update you Internet Explorer using Windows update to prevent any further infections.

1. Open http://windowsupdate.microsoft.com

2. Select all available updates

3. Windows update installs updates and reboots

4. Return to the Windows updates to make sure you have all updated

Clear the Internet Explorer temporary file cache

1. Open Internet Explorer

2. Select "Tools"->"Internet Options..." from the top menu

3. Select "General" tab (this should be visible already)

4. Click from "Temporary Internet files" pane button "Delete Files..."

5. Select checkbox "Delete all offline content"

6. Click "OK"

Scan your computer with F-Secure Anti-Virus to remove any other downloaded components.

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Detailed Description

Details

The Cardown.B is activated when a web site containing the trojan is loaded with unpacthed Microsoft Internet Explorer browser. When the JAR file containing the trojan is executed it uses Microsoft Internet Explorer VerifierBug vulnerability to get full privileges by escaping the Java security, and execute its code.

When executed the trojan modifies the Internet Explorer start page to point to the site where the trojan is downloaded from.

In addition to changing the Internet Explorer settings the trojan downloads trojan downloader win32.StartPage.Y and executes it.

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Write-up: Jarno Niemela, February 6th, 2004;

F-Secure Corporation