Investigating Class 0 SMS Exploits in 5G and Future 6G Architectures

Abstract: Class 0 SMS, commonly known as Flash SMS, is a little-known yet powerful feature in mobile networks that allows silent delivery of messages without storing them on the recipient’s device. Originally designed for urgent communication and network testing, this feature has increasingly drawn attention from cybersecurity researchers due to its potential misuse in surveillance, location tracking, and network probing all without user awareness. While most studies have focused on its impact in legacy systems like GSM and 3G, far less is understood about how Class 0 SMS functions or is exploited within the evolving frameworks of 5G and the emerging 6G networks. This research explores how Class 0 SMS can be leveraged or abused in the context of modern cellular architectures, particularly focusing on 5G networks and early proposals for 6G design. We begin by examining how this message type is handled by current network cores (including 5G NSA and SA modes), highlighting variations across mobile carriers and device types. Through practical experiments and network simulations, we assess the feasibility of using Class 0 SMS for undetected user tracking, signaling-layer attacks, and silent reconnaissance across different generations of mobile connectivity. The research also investigates whether 6G proposals—designed with stronger security and AI-based network management sufficiently account for threats stemming from legacy protocol support like Class 0 SMS. Our findings suggest that despite advancements in authentication and encryption, certain backward-compatible mechanisms may continue to pose serious privacy risks if not carefully addressed. Finally, the paper proposes a set of mitigation strategies, including network-level filters, anomaly detection models, and policy updates, aimed at curbing misuse of this silent channel. As mobile networks grow increasingly intelligent and interconnected, understanding and securing overlooked vectors like Class 0 SMS becomes essential to preserving user trust and privacy in next-generation communications.