Knot Resolver before 5.1.1 allows traffic amplification via a crafted DNS answer from an attacker-controlled server, aka an “NXNSAttack” issue. This is triggered by random subdomains in the NSDNAME in NS records.
cyber-security-group.cs.tau.ac.il/#
www.openwall.com/lists/oss-security/2020/05/19/2
en.blog.nic.cz/2020/05/19/nxnsattack-upgrade-resolvers-to-stop-new-kind-of-random-subdomain-attack/
lists.fedoraproject.org/archives/list/[email protected]/message/76Y4FITMOH6RVPWAANGV7NB2ZHPJJGDQ/
www.knot-resolver.cz/2020-05-19-knot-resolver-5.1.1.html