Network operators deploy currently the 5th generation (5G) of the cellular network and many manufacturers commercialize new 5G end-user devices. It is the first step in the development of 5G still the 5G potential is far from being reached. Network slicing is one of the main 5G technologies for the researcher’s community. Many heterogeneous services like voice communication, video streaming, e-health, vehicular communication are provided and flexibly by exploiting the 5G infrastructure. Security is a critical aspect like every new technology. In this paper, security in 5G network slicing is highlighted life-cycle security, intra-slice security, and inter-slice security along with threats and recommendations are highlighted in this paper.