Security is the most vital issue to be addressed in Wireless Sensor Networks (WSNs). The WSN dominates since it has an effectiveness of applications in numerous fields. Though it has effectiveness towards its applications likewise it is susceptible to two different kinds of attacks (i.e.) external attacks and internal attacks existence of constrained reckoning resources, low memory, inadequate battery lifetime, handling control, and nonexistence of interfere resilient packet. Handle internal attacks such as selective forwarding attacks (SFAs) and black hole attacks (BHA) are considered to be the most common security extortions in wireless sensor networks. The attacker nodes will execute mischievous activities during data communication by creating traffic load, delaying packet delivery, dropping packets selectively or dropping all packets, energy consumption, and depleting all network resources. These attacks can be handled efficiently by implementing the proposed methodology for detecting, preventing, and recovering Cluster Heads (CHs), Cluster Members (CMs), and Transient Nodes (TNs) from SFAs and BHA in intra-cluster multi-hop. It is accomplished by proposing a robust strategy for overcoming internal attacks on cluster head, cluster member, and transient node. The Fuzzy C-Means clustering is used to discover the prominent cluster head. The uncertainty entropy model is used to detect internal attacks by removing the malicious node from the transition path. The intermediate node is been selected based on the degree and dimension. The experimental results of the proposed Robust Tristate Security Mechanism (RTSSM) against SFAs and BHA are evaluated with packet delivery ratio, throughput, and packet drop and the results prove the effectiveness of the proposed methodology and it also aids in the extension of the network lifetime.