This book constitutes the refereed proceedings of the 17th International Conference on Network and System Security, NSS 2023, held in Canterbury, UK, August 14–16, 2023.The 12 full and 9 short papers presented together with 2 invited talks in this book were carefully reviewed and selected from 64 submissions. They focus on Attacks and Malware, Blockchain, Security through Hardware, Machine learning and much more.