5G has introduced various emerging demands for new services and technologies that raised the bar for quality of service, latency, handovers, and data rates. Such diverse and perplexing network requirements bring numerous issues, among which security stands in the first row. The backhaul, which can be implemented as a wired or wireless solution, serves as a bridge between the radio access and core networks assuring connectivity to end users. The recent trends in backhaul usage rely on wireless technologies implemented using point-to-point (PTP) or point-to-multipoint (P2MP) configurations. Unfortunately, due to the nature of the transmission medium, the wireless backhaul is vulnerable and exposed to more various security threats and attacks than the wired one. In order to protect the backhaul, there have been several researches, whose authentication and key exchange scheme mainly depends on the existing security standards such as transport layer security (TLS), Internet Key Exchange version 1 (IKEv1), IKEv2, Host Identity Protocol (HIP), and Authentication and Key Agreement (AKA). However, such security standards cannot completely fulfil the security requirements including security policy update, key update, and balancing between security and efficiency, which are necessary for the emerging 5G networks. This is basically the motive behind why we study and propose a new security protocol for the backhaul link of wireless access network based on P2MP model. The proposed protocol is designed to be 5G-aware, and provides mutual authentication, perfect forward secrecy, confidentiality, integrity, secure key exchange, security policy update, key update, and balancing trade-off between efficiency and security while preventing resource exhaustion attacks. The protocol's correctness is formally verified by the well-known formal security analysis tools: BAN-logic and Scyther. Moreover, the derived lemmas prove that the security requirements are satisfied. Finally, from a comparison analysis, it is shown that the proposed protocol is better than other standard protocols.