Our environment is getting smarter and smarter and we will reach billions of IoT devices. Being able to implement the IoT properly requires several challenges to take up. This is why the LPWAN technologies were recently introduced. Among many of LPWAN candidate, lora’s power efficiency and long rang features have made it of of the most important candidate for the IoT technology. The constraints of duty cycle limitation was studied in [1] where a shared duty cycle was proposed using different allocation strategies. In this paper, we propose to study the vulnerability of a proposed Enhanced LoRaWAN duty cycle that may turn into an attack: bit flipping and spoofing attack. We propose and evaluate a solution to guaranteed the security in a dynamic behavior of a duty cycle.