LoRaWAN (Long Range Wide Area Network) is rapidly gaining attention in the Internet of Things (IoT) due to its ability to provide a long-range wireless network at low energy consumption. However, with the Aloha MAC protocol, LoRaWAN faces the challenge of malicious behaviors from compromised nodes. Compromised nodes can take greedy behaviors by breaking network rules to improve their performance or obtain more network resources. This study proposes and investigates different greedy behaviors of infected nodes in LoRaWAN on the MAC layer. A straightforward double judgment detection method is proposed. The simulation results show that although the MAC layer of LoRaWAN is robust and resilient against greedy behavior by design, it can still be negatively affected by high-intensity greedy behavior. Moreover, the simulation results also show the high performance of the proposed detection method in different greedy behavior scenarios.