The 20th International Conference on Risks and Security of Internet and Systems (CRiSIS) in 2025 continues its tradition of addressing critical security challenges in Internet-connected applications, networks, and systems. The indispensability of the Internet for information exchange among diverse user groups and organizations has led to heightened risks around security and privacy. This vulnerability is exacerbated by the sophistication of online attacks, the proliferation of cybercrime, and the readily available tools for attackers, who are increasingly motivated and skilled. The advent of complex technologies, including pervasive computing, mobile, and wireless devices and networks, introduces new security challenges, necessitating the deployment of advanced security mechanisms and techniques. These advancements are crucial for protecting critical sectors such as energy, transportation, health, defense, banking, critical infrastructures, embedded systems and networks, avionics systems, and more, ensuring an acceptable level of security assurance. CRiSIS 2025 serves as an essential platform for stakeholders in computer and network security from the industrial, academic, and governmental sectors to convene, share insights, and showcase the latest developments in combating Internet-related security threats, vulnerabilities, and the necessary countermeasures to address them.