NETBIOS Session Service

• The NetBIOS SSN (Session Service) refers to a service that operates over NetBIOS (Network Basic Input/Output System)
• a protocol used for communication on local area networks (LANs)
• The SSN service is used to provide file sharing and printer sharing functionality
• commonly seen in older Windows networks and other systems that rely on NetBIOS over TCP/IP.

TCP 139 is perhaps the most well-known Windows port. It is used to transfer files over a network. Systems use this port for both null-session establishment as well as file and printer sharing. A system administrator considering the restriction of access to ports on a Windows system should make the restriction of TCP 139 a top priority. An improperly configured TCP 139 port can allow an intruder to gain unauthorized access to critical system files or the complete file system, resulting in data theft or other malicious activities.