This book constitutes the refereed post-proceedings of the 7th International Conference on Mobile Internet Security, MobiSec 2023, held in Okinawa, Japan, in December 19–21, 2023. The 21 full papers presented were carefully reviewed and selected from 70 submissions. The papers are organized in the following topical sections: 5G and 6G security; cryptography; machine learning-based security; identification and authentication; network design and security.