This indicates an attack attempt to exploit a Denial of Service vulnerability in Dnsmasq.
The vulnerability is due to an input validation error when handling malformed requests. A remote attacker may be able to exploit this to cause a denial of service condition on the affected system.
DNSmasq/Mikrotik DNSmasq 2.77
Denial of Service: Remote attackers can crash vulnerable systems.
Apply the most recent upgrade or patch from the vendor.