This indicates an attempt to exploit a Denial of Service vulnerability in PowerDNS.
The vulnerability is due to an error when the vulnerable software processes a DNS query with the dot character inside labels. A remote attacker may be able to exploit this to cause a denial of service condition on the affected system.
PowerDNS PowerDNS Authoritative Server 3.x prior to 3.4.10
Denial of Service: Remote attackers can crash vulnerable systems.
Apply the most recent upgrade or patch from the vendor.