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.
Upstream has issued an advisory today (September 21):
The issue is fixed upstream in 1.16.3:
Created unbound tracking bugs for this issue:
Affects: fedora-all [bug 2128953]