This indicates an attempt to exploit a Denial of Service vulnerability in PowerDNS.
The vulnerability is due to a validation error when the vulnerable software handles a DNS query. A remote attacker may be able to exploit this to cause a denial of service condition on the affected system.
PowerDNS PowerDNS Recursor 3.6.0
Denial of Service: Remote attackers can crash vulnerable systems.
Apply the most recent upgrade or patch from the vendor.