Abstract
The integration of 5G communication into Smart Grid (SG) systems offers significant advancements in reliability, low-latency control, and real-time monitoring. However, it also expands the cyber-attack surface, particularly exposing critical infrastructure to Denial-of-Service (DoS) threats. This paper addresses three key research questions related to Testbed design and development, practical attack & execution feasibility, and impact evaluation within 5G-enabled smart grids. To support this investigation, we design and implement a commercial-grade private 5G smart grid testbed that emulates realistic Information Technology (IT) and Operational Technology (OT) conditions. Using this testbed, we systematically model and execute various DoS attack scenarios targeting different layers of the smart grid communication stack. We choose a selective DoS taxonomy to identify vulnerable components of the communication infrastructure, focusing on 5G signaling. Experimental results show that volumetric DoS attacks significantly degrade network Key Performance Indicators (KPIs), such as increased packet loss, jitter, and delayed control responses, demonstrating their disruptive potential in smart grid environments. Our findings not only expose practical vulnerabilities, but also highlight the value of testbed-driven security assessments for validating mitigation techniques. This research contributes a reproducible platform and structured threat framework for advancing the cyber-resilience of future 5G-integrated energy systems.