DNS Amplification Attacks

A misconfigured Domain Name System (DNS) server can be exploited to participate in a Distributed Denial of Service (DDoS) attack. A Domain Name Server (DNS) Amplification attack is a popular form of Distributed Denial of Service (DDoS) that relies on the use of publically accessible open recursive DNS servers to overwhelm a victim system with DNS response traffic. The basic attack technique consists of an attacker sending a DNS name lookup request to an open recursive DNS server with the source address spoofed to be the victim's address. When the DNS server sends the DNS record response, it is sent instead to the victim. Attackers will typically submit a request for as much zone information as possible to maximize the amplification effect. Because the size of the response is typically considerably larger than the request, the attacker is able to amplify the volume of traffic directed at the victim. By leveraging a botnet to perform additional spoofed DNS queries, an attacker can produce an overwhelming amount of traffic with little effort. Additionally, because the responses are legitimate data coming from valid servers, it is especially difficult to block these types of attacks.