Port scanning is the process of attempting to connect to various network ports on a computing endpoint to determine which ports are open and which services are running on them. It is a common method used by hackers to identify vulnerabilities in a network or system. By determining which ports are open, an attacker can identify which services and applications are running on a device and potentially exploit any known vulnerabilities in those services. Consequently, it is important to detect port scanning because it is often the first step in a cyber attack. By identifying port scanning attempts, cybersecurity professionals can take proactive measures to protect the systems and networks before an attacker has a chance to exploit any vulnerabilities. Against this background, researchers have worked for over a decade to develop robust methods to detect port scanning. While there have been various surveys, none have focused solely on machine learning based detection schemes specific to port scans. Accordingly, we provide a systematic review of 15 papers published between February 2021 and January 2023. We extract critical information such as training dataset, algorithm used, technique, and model accuracy. We also collect unresolved challenges and ideas for future work. The outcomes are significant for researchers looking to step off from the latest work and for practitioners interested in novel mechanisms to detect the early stages of cyber attack.