Node misbehavior problems have received increased attention in multicasting in Mobile ad hoc networks (MANET). The misbehaving nodes can be either selfish or malicious nodes. The main goal of the malicious nodes is to intentionally interrupt the network using various attacks. Hence it is essential to develop a mitigation technique against misbehaving attacks. In this paper, we propose a misbehaving attack mitigation technique for multicast security in MANET. Initially the nodes are categorized into strong and weak nodes according to their stability index which is estimated based on the link availability and mobility. Among the selected strong nodes, the nodes with high reputation index are chosen as initiator nodes which assist in attack detection. The initiator node detects the misbehaving nodes based on their packet delivery ratio. Upon misbehaving node detection, initiators employ recrimination based attack isolation technique to isolate the attacker node during data transmission. By simulation results we show that the proposed technique enhances security in MANET.