Port 139 netbios, It operates primarily on UDP ports 137 and 138 and TCP port 139. When Microsoft documentation says “earlier operating systems” in guidance about SMB and NetBIOS over TCP/IP (NBT), it’s talking about legacy Windows releases that either require NetBIOS/port 139 for file sharing, or commonly depended on NetBIOS for name resolution and network browsing. System administrators should disable NetBIOS over TCP/IP on all devices across the network. 3 days ago · TCP Port 139 is a network port used for NetBIOS Session Service to enable file and printer sharing through the Server Message Block (SMB) protocol in Windows networks. 6 days ago · Based on your previous scan, that means only against the host that has TCP ports 139 (NetBIOS-SSN) and 445 (microsoft-ds) open, which in your case is your Windows 7 system. In many environments, 445 is treated as higher-risk and filtered more aggressively. The earlier version of SMB (SMB 1. Learn about its vulnerabilities and how to protect it. Mar 14, 2025 · Guidance Disabling Action By default, NetBIOS uses TCP port 139 to provide session services, and uses UDP ports 137 and 138 to provide name services and datagram services respectively. 2 days ago · What NetBIOS over TCP/IP Actually Does NetBIOS over TCP/IP allows computers to identify each other using NetBIOS names instead of DNS. Oct 20, 2023 · What is Port 139? by Colin Cohen | Published on October 20, 2023 Port 139 is a dedicated port for providing session services for the Server Message Block (SMB) protocol over NetBIOS, which is primarily used for sharing printers and files in a Windows-based network. I just wanted to add that for versions of Windows from Windows 2000 and onward, all of the legacy NetBIOS functionality from ports 137, 138 and 139 is by default handled by SMB (Server Message Block) over port 445. These services were once essential for Windows file and printer sharing. Feb 12, 2026 · A roadmap of ports, protocols, and services that are required by Microsoft client and server operating systems, server-based applications, and their subcomponents to function in a segmented network. May 22, 2025 · NetBIOS over TCP/IP has several security implications, including the potential for attacks on TCP port 139 and UDP port 137, and the discovery of devices on the network through NetBIOS name resolution. However, when exposed, it becomes a high-risk attack surface for SMB-based exploits. Apr 20, 2022 · Admins need to know the SMB port number when it comes to setting up firewalls in Windows networks. Although modern systems primarily use Port 445, Port 139 is still active in legacy environments. 1 day ago · Microsoft publishes port requirements that explicitly list SMB on 445 and NetBIOS Session Service on 139. Nov 10, 2024 · What is Port 139? Port 139 is a TCP port in the Windows operating system associated with the NetBIOS Session Service. . Left open, it can be a security risk. 0) was originally designed to operate on NetBIOS over TCP/IP (NBT), which uses port TCP 139 for session services, port TCP/UDP 137 for name services, and port UDP 138 for datagram services. Jul 19, 2024 · Port 139 is the dedicated port for SMB over NetBIOS. The official service name for port 139 is ‘netbios-ssn,’ and the port number is registered with the Internet Assigned Numbers Authority (IANA).


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