A smart grid is an advanced power system that uses digital technology like sensors and software to manage electricity supply and demand. The success of a smart grid depends on how well its physical infrastructure works together with the digital systems that handle data collection, processing, and control, which are called Cyber-Physical Systems (CPS). However, the security of CPSs is a growing concern for re-searchers and industries. For this research, we used theoretical methods, focusing on literature analysis to evaluate security gaps in CPS in smart grids. This paper looks at the overview of a CPS, including its architecture and the Smart Grid Cyber-Physical System (SG-CPS) architecture. It discusses the objectives of SG cyber security while also discussing attacks faced by CPSs in smart grids; these include false data injection, bad data injection, denial of service, replay, and physical attacks. The paper then reviews existing security measures such as access controls, encryption, firewalls, and intrusion detection systems. Finally, a discussion is made on the challenges facing CPS security as well as cybersecurity standards and protocols.