Since the field of wireless technology is growing rapidly, security is becoming a major concern. A variety of security problems are being addressed, and much research work is taking place in order to provide adequate security to prevent hackers from disrupting network service. Wireless networks follow the IEEE 802.11 standard to transmit and receive packets. The IEEE 802.11 MAC protocol is designed in such a way to provide an equal share of throughput among all nodes in a network. Users who misbehave could modify the IEEE 802.11 MAC protocol, thus causing major security threats including substantial bandwidth degradation of other users. This thesis addresses the misbehavior of a node caused by altering the packet size. For a node to acquire higher throughput compared to other genuine nodes in the network, its packet size could be set higher than that of the genuine nodes. In order to protect against this sort of misbehavior, a special algorithm, which is a slight modification of the IEEE 802.11 MAC protocol, was developed. This algorithm is based on the notion of receiver-assigned backoff, which has already been used to deal with other types of misbehavior. The packet size-based misbehavior was modeled mathematically using queuing theory, and an appropriate reaction strategy was deduced from the analytical results. It was shown that the proposed approach reduces the effectiveness of misbehavior and leads to fairness in the network.