The emergence of cloud computing aspects and its development by large high-tech companies promotes the integration of VoIP services in the cloud computing. This integration allows the use of available resources in the cloud and therefore to have a scalable and interoperable VoIP service and allowing new opportunities for VoIP architectures expansion. However, these services are exposed to attacks inherited from the VoIP application layer and attacks caused by the openness of the cloud architecture. As the cloud is used to establish an flooding-based attack, we will use the resources proposed and the cloud architecture to provide a security solution. We propose a risk management strategy for VoIP cloud to manage risk and nec- essary countermeasures to adapt the exposure of these services. This approach is based on the outsourcing of countermeasures to be used as an independent service. We describe the mathematical model used to assess the risk, the architecture of our security solution and namely the different components and we show the exchange of SIP messages to apply safeguards. We propose different strategies to implement countermeasures in the failure case which may affect the VoIP services. Finally, we quantify the risk benefit and the induced cost of the different strategies performed by the Monte Carlo simulation.