Wireless Sensor Network (WSN) is made up two or more interconnected sensor nodes wirelessly. These nodes may be deployed either in open or closed environment. As these nodes communicates wirelessly and deployed in open environment there are always threat of security of nodes as well as data communicated. In order to making secure communication over WSN there should be some security mechanism. In this paper a common security mechanism is proposed to mitigate pulse delay attack and node replication. This mechanism includes detection and then mitigation.