Machine-to-Machine (M2M) paradigm is one of the main concern of Internet of Things (IoT). Its scope is to interconnect billions of heterogeneous devices able to interact in various application domains. Since M2M suffers from a high vertical fragmentation of current M2M markets and lacks of standards, the European Telecommunications Standards Institute (ETSI) released a set of specifications for a common M2M service platform. An ETSI-compliant M2M service platform has been proposed in the context of the open source OM2M project. However such a platform currently only marginally addresses security and privacy issues, which are fundamental requirements for its large-scale adoption. Therefore, an extension of the OM2M platform is proposed, defining a new policy enforcement plugin, which aims to manage the access to the resources provided by the platform itself and to handle any violation attempts of the policies.