When attachment blocking is enabled, messages are blocked if prohibited file types are in a .zip archive. If the same files are in the .rar archive, then GWAVA 6.5 does not block the files.
Moreover, I see quite serious threats via e-mail when .scr or .js are in the .rar archive, which has been renamed .gz.

Is it possible to block such attachments on GWAVA 6.5?

A complete ban on .rar files is not possible.