This book constitutes the proceedings of the 5th International Symposium on Cyberspace Safety and Security, CSS 2013, held in Zhangjiajie, China, in November 2013. The 30 full papers presented in this volume were carefully reviewed and selected from 105 submissions. In addition the book contains 6 workshop papers. The papers are organized in topical sections named: data and applications security; network and communications security; software and systems security; and cloud security and cyberspace safety.