In medical fields, a wearable body area sensors network is a network of sensors placed inside human bodies or on their skin. These multi-functional sensors provide all patients and medical personnel with optimized and comfortable services. The patient’s physiological information transferred in this network is very sensitive and confidential; Therefore, transmitting through an insecure channel requires high anonymity, un-traceability, and privacy-preserving of personal data. Furthermore, the wearable body area network is a small part of the Internet of Things (IoT) community, and as the devices are resource-constraint, lightweight protocols are needed to guarantee the information’s authenticity, confidentiality, and integrity. Hence, a large number of schemes were proposed by different researchers to improve the reliability of the protocols. Recently Ankur Gupta and his colleagues proposed a lightweight mutual authentication and key agreement protocol and proved its security against well-known attacks. In this paper, we will demonstrate that their proposed protocol is vulnerable to the sensor node impersonation attack and does not provide the necessary security for communicating data; Then, we will offer a new solution to overcome this problem.