An ever-existing concern is the lack of security due to the very fact that the technology is wireless and is vulnerable to security threats & attacks. Also, among the wide-spread characteristics of a CR, self-organized security management is one of prime considerations. Each layer in cognitive radios is susceptible to widespread threats and security attacks. In fact, this paper reveals a detailed tabulation of the possible security threats/attacks faced by cognitive radios & cognitive radio networks in the link and MAC layer, along with the current state-of-the-art to detect the corresponding attacks and discuss the possible countermeasures for the same.