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3.21. Self-Contained Environment Dependency

One interesting dependency appears when malicious code carries its own environment to the platform. The W32/Franvir virus family offers a good example.

Franvir is clearly a Win32 application. It is compiled with Borland Delphi to a 32-bit PE program. However, the actual Win32 binary part is known as the Game Maker, written by Mark Overmars of the Netherlands (http://www.cs.uu.nl/people/markov/gmaker/doc.html).

The Franvir virus was written by a French virus writer using the script language of Game Maker, called GML (Game Maker Language). This is only available in the registered version of Game Maker, which provides developers with security options for using these functions (turning them on and off). It is up to the developer to set the security settings; therefore, a malicious author can easily use GML of Game Maker for virus writing.

Game Maker is a professional game developer environment. Hundreds of brilliant games have been created in it by professionals. It can be used to develop all kinds of games, including scrolling shooters, puzzle games, and even isometric games. For instance, the shooter game called Doomed was created using Game Maker (see Figure 3.14).

Figure 3.14. Doomed in action.


GML provides functions for Registry, File, and program execution. The File operation functions are extremely rich and provide high flexibility for game developers to install and execute programsbut they also can be used by malicious attackers. Some of the functions of GML include the following:

file_exists(fname)
file_delete(fname)
file_copy(fname,newname)
file_open_write(fname)
directory_create(dname)
file_find_first(mask,attr)
file_find_next()
file_attributes(fname,attr)
registry_write_string_ext()

GML scripts are stored in the resources of Game Maker, but they are accessed and executed by the environment, the interpreter in Game Maker itself. Franvir is an encrypted GML script. It copies itself all over the hard disk under various existing program names. It also installs itself to local P2P (peer-to-peer) folders or even creates the shared folder for KaZaA if the directory is not installed ("kazaa\my shared folder\") and changes the KaZaA settings to share the folder. Furthermore, it does damage by deleting the win.com file of Windows. Thus, ultimately Franvir must be classified as a Win32 P2P worm. In reality, however, it is a GML script that is carried by its own environment to new platforms. When the virus successfully executes, it eventually uses the show_message() function to display the false error message shown in Figure 3.15.

Figure 3.15. The false error message of Franvir.


The virus could ultimately offer to play a game such as the DOS virus, Playgame, instead of executing the malicious file delete action as an activation routine, but well...what can we expect from a typical virus writer?

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