Unmanned Aerial Vehicles (UAV) or drones is a technology with a huge potential for proving different efficient solutions in the smart city. It has been mostly adopted by military, aviation, civil, and commercial sectors for audio and video surveillance. The communication and security challenges of UAV is well mentioned by researchers and organizations (defense) around the world, although many of the challenges remain unresolved (especially for sensitive and consumer-related applications). Moreover, the conventional network systems may not be very efficient in dealing with the dynamic requirements of UAVs. As the UAVs are generally deployed in tough environments and terrains, therefore it is quite essential to provide a strong and secure network. Motivated from these facts, this paper presents an extensive survey on security issues in 5G-enabled UAV networks as per the literature published till the fourth quarter of 2019. It also presents the taxonomy of existing security issues in 5G-enabled UAV networks. Based on the findings from the survey, we present a Blockchain (BC)-based security solution and a summary of research challenges in the integration of BC with 5G-enabled UAV. Then, we present a case study of implementing BC with UAVs to secure industrial applications.