CVE-2022-3204

A vulnerability named ‘Non-Responsive Delegation Attack’ (NRDelegation
Attack) has been discovered in various DNS resolving software. The
NRDelegation Attack works by having a malicious delegation with a
considerable number of non responsive nameservers. The attack starts by
querying a resolver for a record that relies on those unresponsive
nameservers. The attack can cause a resolver to spend a lot of
time/resources resolving records under a malicious delegation point where a
considerable number of unresponsive NS records reside. It can trigger high
CPU usage in some resolver implementations that continually look in the
cache for resolved NS records in that delegation. This can lead to degraded
performance and eventually denial of service in orchestrated attacks.
Unbound does not suffer from high CPU usage, but resources are still needed
for resolving the malicious delegation. Unbound will keep trying to resolve
the record until hard limits are reached. Based on the nature of the attack
and the replies, different limits could be reached. From version 1.16.3 on,
Unbound introduces fixes for better performance when under load, by cutting
opportunistic queries for nameserver discovery and DNSKEY prefetching and
limiting the number of times a delegation point can issue a cache lookup
for missing records.