In recent years, unmanned aerial systems (UAS) have been widely used in both military and civilian fields. However, their open-source software and protocols have made their security vulnerable, resulting in a growing number of cybersecurity issues. This paper provides a comprehensive review of UAS cybersecurity research, with a focus on attack and defense technologies. Regarding UAS being a system that integrates software and hardware and can work independently with complex tasks, this paper analyzes the UAS architecture and classifies security threats into four categories: communication network security, software security, payload security, and intelligent security. Additionally, it provides an overview of existing threat assessment methods. This paper also highlights representative research progress in UAS cyberattacks and defense technologies in the four identified categories. Finally, this paper examines the current research status and future prospects of UAS cybersecurity.