The LNCS 12653 constitute the proceedings of the 12th International Symposium on Cyberspace Safety and Security, CSS 2020, held in Haikou, China, in December 2020.The 37 regular papers presented in this book were carefully reviewed and selected from 82 submissions. The papers focuses on Cyberspace Safety and Security, such as authentication, access control, availability, integrity, privacy, confidentiality, dependability and sustainability issues of cyberspace.