Domain Name System (DNS) is one of the most crucial components of the Internet. However, due to the vulnerability of DNS, its security has been continuously challenged in recent years. In order to thoroughly understand the root cause of the security risks in the DNS, researches in DNS security are surveyed, and vulnerabilities in DNS and corresponding countermeasures are summarized. First, based on the protocol design and implementation of DNS, weaknesses in DNS fall into 5 categories: cache poisoning, denial of service, software vulnerabilities, information leakage and unauthorized data manipulation. Then, fundamental properties and defense approaches for the 5 categories are analyzed. Next, to improve the Internet name service, new secure DNS architectures are analyzed and compared. And finally, future aspects of research in DNS security are discussed.