Preserving the privacy of users' information is an essential requirement in information management systems. The emergence of context-aware services makes protecting the users' information an even greater challenge. Addressing this challenge requires an automatic mechanism that allows users to control their information at real-time. In this context, we propose a middleware called Context-Aware PRIvacy-preserving system Supervised by users (CAPRIS), which provides users with groups of policies that form profiles to protect their privacy in the environment in which they are located. CAPRIS lets users to control and supervise at real-time the information they are revealing to other users who use context-aware services. Semantic technologies play a key role in our solution. We use ontologies for shaping the space and context, and semantic rules defining the privacy policies that form the context-aware profiles. Some experiments measuring the throughput and scalability of CAPRIS confirm that our solution improves other related works.