This indicates an attack attempt to exploit a Denial of Service vulnerability in ISC BIND.
The vulnerability is due to an error when vulnerable module handles a crafted query response with NSEC record. A remote attacker may be able to exploit this to cause a denial of service condition on the affected system.
ISC BIND 9.9.9-P4
ISC BIND 9.9.9-S6
ISC BIND 9.10.4-P4
ISC BIND 9.11.0-P1
Denial of Service: Remote attackers can crash vulnerable systems or services
Apply the most recent upgrade or patch from the vendor.