RealNetworks has verified this specific exploit. Customers running UNIX versions of RealServer are not susceptible to this exact attack. The exploit only works on the admin port of the server, which is randomly chosen at install. By default, this makes the port unique for each RealServer. The published exploit only works if the RealServer is installed in the default server directory.
Users have an option to install in a different directory and often do.
If the user installed the RealServer in a different directory then the exploit does not work. The access control feature lets you associate certain client addresses with permissions to connect to certain RealServer ports. When this feature is used the exploit is no longer possible.