Software Defined Network (SDN) decouples the responsibilities of route management and data transmission of network devices present in network infrastructure. It integrates the control responsibility at the centralized software component which is known as controller. This centralized aggregation of responsibilities may result the single point of failure in the case malicious attack at the controller side. These attacks may also affect the traffic flow and network devices. The security issues due to such malicious attacks in SDN are dominating challenges in the implementation and utilization of opportunities provided by this new paradigm. In this paper we have investigated the several research papers related to proposal of new research trends for security and suggestions which fulfil the security requirements like confidentiality, integrity, availability, authenticity, authorization, nonrepudiation, consistency, fast responsiveness and adaptation. We have also investigated the new future research for creating the attack free environment for implementing the SDN.