This indicates an attack attempt against an Information Disclosure vulnerability in Samba.
The vulnerability is caused by an error when the vulnerable software handles a specially crafted request. A remote attacker can exploit this to gain unauthorized access to sensitive information.
Samba 3.x and 4.x before 4.1.22
Samba 4.2.x before 4.2.7
Samba 4.3.x before 4.3.3
Information Disclosure: Remote attackers can gain sensitive information from vulnerable systems.
Apply the most recent upgrade or patch from the vendor.