This book constitutes the proceedings of the 17th International Conference on Risks and Security of Internet and Systems, CRiSIS 2021, which took place during November 11-13, 2021. The conference was originally planned to take place in Ames, IA, USA, but had to change to an online format due to the COVID-19 pandemic. The 9 full and 3 short papers included in this volume were carefully reviewed and selected from 23 submissions. The papers were organized in topical sections named: CPS and hardware security; attacks, responses, and security management; network and data security.