Israeli cybersecurity researchers have disclosed details about a new flaw impacting DNS protocol that can be exploited to launch amplified, large-scale distributed denial-of-service (DDoS) attacks to takedown targeted websites. Called NXNSAttack, the flaw hinges on the DNS delegation mechanism to force DNS resolvers to generate more DNS queries to authoritative servers of attacker's choice, potentially causing a botnet-scale disruption to online services.
Following responsible disclosure of NXNSAttack, several of the companies in charge of the internet infrastructure, including PowerDNS (CVE-2020-10995), CZ.NIC (CVE-2020-12667), Cloudflare, Google, Amazon, Microsoft, Oracle-owned Dyn, Verisign, and IBM Quad9, have patched their software to address the problem. The DNS infrastructure has been previously at the receiving end of a rash of DDoS attacks through the infamous Mirai botnet, including those against Dyn DNS service in 2016, crippling some of the world's biggest sites, including Twitter, Netflix, Amazon, and Spotify.
The researchers said the attack can amplify the number of packets exchanged by the recursive resolver by as much as a factor of more than 1,620, thereby overwhelming not only the DNS resolvers with more requests they can handle, but also flood the target domain with superfluous requests and take it down. What's more, using a botnet such as the Mirai as a DNS client can further augment the scale of the attack. It's highly recommended that network administrators who run their own DNS servers update their DNS resolver software to the latest version.