The initial access phase of the 5G system remains sensitive because the base station (gNB) must allocate radio resources before the user is fully authenticated. In particular, the random access channel (RACH) procedure can be abused to generate large numbers of incomplete connection attempts, creating a signaling storm that consumes gNB resources and prevents legitimate users from connecting successfully. In this paper, we implement this signaling storm attack using the OpenAirInterface project and validate it on a real testbed composed of software-defined radios and commercial phones. We then design and implement a lightweight mitigation technique that operates directly at the gNB by monitoring and acting on suspicious half-open connections. To make the system observable in practice, we also develop a network management interface that visualizes the network state in real time and highlights suspicious activity during the attack phase. Finally, the work is released as open source so that other researchers can reproduce our results, build on the implementation, and evaluate new mitigation strategies.

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