Advances in communication technologies as well as the availability of the Internet and Internet of Things (IoT) devices enable users to access various services on the internet. However, open communication with IoT devices can be attacked. Recently, Rana et al. proposed a secure key agreement protocol using RLWE. In this paper, we exploited the vulnerability of Rana et al.'s protocol by using a key mismatch attack. Moreover, it has been shown how an adversary who plays a user's role recovers the server's long-term secret key.