In this paper we present a model for expressing attacks on control protocols that involve the exchange of messages. Attacks are modeled using the notion of an attacker who can block and/or fabricate messages. These two attack mechanisms cover a variety of scenarios ranging from power grid failures to cyber attacks on oil pipelines. The model provides a method to syntactically express communication systems and attacks, which supports the development of attack and defense strategies. For demonstration purposes, an attack instance is modeled that shows how a targeted messaging attack can result in the rupture of a gas pipeline.