This indicates an attack attempt to exploit a Null Pointer Dereference Vulnerability in Samba.
The vulnerability is due to an error in the vulnerable application when handling a maliciously crafted request. A remote attacker may be able to exploit this to cause a denial of service condition on the affected system.
Samba 4.8.x prior to 4.8.4
Denial of Service: Remote attackers can crash vulnerable systems.
Apply the most recent upgrade or patch from the vendor: