This indicates an attack attempt to exploit a Denial of Service vulnerability in Samba.
The vulnerability is due to insufficient sanitizing when handling a maliciously crafted DNS Query. A remote attacker can exploit this to cause a denial of service condition on vulnerable systems.
Samba Team Samba 4.0.x prior to 4.0.18
Samba Team Samba 4.1.x prior to 4.1.8
Denial of Service: Remote attackers can crash vulnerable systems.
Apply the most recent upgrade or patch from the vendor.