Quantum Key Distribution (QKD) protocols theo- retically propose a high-security level based on the advantages of quantum computing. This paper analyze the security level of one of the most well-known QKD protocols, BB84, against the man-in-the-middle attack strategy. Specifically, we leverage quantum entanglement to enhance communication security by the injection of a malicious photon in the middle of transmission. In the security analysis, we measure the variation in mutual information between the sender-receiver and sender-attacker to assess the protocol's resilience against potential attacks.