F-Secure Virus Descriptions : Cardown

Cardown.A 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 download and install Startpage.Y trojan component.

Technical details

Cardown is a Java applet that is heavily obfuscated and uses scrambling in it's strings. The trojan is not packaged in to a Jar file so each component class file is individually loaded when trojan executes, so in most cases the user will get a warning about the first component file and will not receive the rest of the malware.

When the trojan is executed it uses Microsoft Internet Explorer VerifierBug vulnerability to get full privileges by escaping the Java security, and execute its code. Then the trojan downloads bootconf.exe into Windows directory (default C:\Windows) and modifies registry so that the trojan starts automatically at Windows startup.

Further information about the vulnerability in the Microsoft Java VM, including a fix, is available at: http://www.microsoft.com/technet/security/bulletin/ms03-011.asp

Disinfection

The trojan makes following registry changes:

Added registry keys:
Software\Microsoft\Windows\CurrentVersion\Run\Internat Conf

Removed registry keys:
Software\Microsoft\Windows\CurrentVersion\Explorer\ReconfLast
Software\Microsoft\Windows\CurrentVersion\Explorer\Advanced\StartConfCnt

To remove Cardown.A from your system:

-Apply the fix to the Java VM vulnerability
-Clear temporary Internet files cache
-Scan your system to locate the Startpage.Y trojan

Jarno Niemela, 3th of September, 2003;