The role and security of firewalls in cyber-physical cloud computing

Clouds are here to stay, and the same holds for cyber-physical systems—not to forget their combination. In light of these changing paradigms, it is of utter importance to reconsider security as both introduce new challenges. Overcoming the concept of zoned networks, clouds make former internal traffic traveling the Internet. Cyber-physical systems include physical parts into computing and make them potential targets for cyber attacks—a dare as a high number of physical parts have originally been developed to be stand-alone. Cyber-physical cloud computing reinforces the need for a thoughtful security concept. Firewalls are among the basic building blocks in network security and are offered by various cloud providers; however, the question on their quality of protection arises. In this paper, we assess firewall offers of five major cloud providers with respect to cyber-physical system integration. Therefore, we study their default configuration, configuration capabilities, documentation, and filtering behavior. We developed an extendible firewall monitoring tool that enables customers to probe their provider’s filtering behavior— an information of interest for risk management or further security consideration. Re-assessing filtering behavior, we found that all offered firewalls have evolved over a time period of more than a year: Configuration possibilities have been enhanced, more illegitimate packets are filtered now, and stateful behavior was discovered at a certain provider.