Concepts and technologies for detecting and blocking Domain Name System (“DNS”) cache poisoning attacks are provided. An inline detector and blocker apparatus implements a detection algorithm to monitor DNS response packets and detects a DNS cache poisoning attack utilizing the detection algorithm. The inline detector and blocker apparatus detects the DNS cache poisoning attack by receiving a DNS response packet and determining that the response packet includes poison data. The poison data may be included within an additional section of the response packet and/or an answer section of the response packet. As appropriate, the inline detector and blocker apparatus removes the additional section and/or the answer section of the response packet to effectively block the poison data from being cached by a DNS caching resolver.