The Server Message Block Protocol (SMB) is a network protocol that allows computers to communicate with each other seamlessly and securely. It facilitates the sharing of files, printers, serial ports, and data transmission between two or more machines on a single network – allowing for authenticated inter-process communication as well. In short, an SMB port creates an intuitive way for both local and remote devices to converse effectively.

How SMB Protocol Works

SMB leverages a client-server model, where the server responds to requests made by its clients. This response-request protocol makes it possible for devices on different networks to share files with one another efficiently and effectively.

Once connected, users and applications can request a file server for access to resources like named pipes, printer sharing, and mail slots on the remote system. This grants a user of the full application control over documents stored remotely – they can open files, read them, move them around, create new ones or update existing ones with ease.

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SMB Protocol Dialects

Popular SMB implementations include:

SMB 1.0 (1984)

IBM created this file-sharing system for DOS with the purpose of reducing network traffic by employing a client-side caching mechanism known as opportunistic locking.

Samba (1992)

Samba, an open-source translation of the SMB protocol and Microsoft Active Directory for Unix systems and Linux distributions, allows you to easily share files among your Windows clients and Linux/Unix servers. Samba also ensures secure authentication & authorization as well as reliable name resolution & service announcements between these two platforms.

CIFS (1996)

Microsoft introduced this revolutionary SMB dialect with the launch of Windows 95, equipping users to transport data directly over TCP/IP networks and enjoy larger file sizes, symbolic links, and hard links.

NQ (1998)

Visuality Systems’ NQ family of SMB clients and servers brings portability to non-Windows platforms like Linux, iOS, and Android. All the versions are equipped with cutting-edge features like SMB 3.1.1 dialect support for an improved user experience.

Netsmb (2004)

‍Netsmb is an innovative family of SMB client and server applications built directly into BSD operating systems.

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SMB 2.0 (2006)

SMB v2, released with Windows Vista and Server 2008, decreased inefficiency which led to improved performance, amplified scalability & resiliency as well as enabled support for WAN acceleration.

Tuxera SMB (2009)

Tuxera, an exclusive SMB implementation, operates in the kernel or user-space environment.

Likewise (2009)

Likewise designed a multiprotocol, identity-aware CIFS/SMB platform to allow access to files in Linux/Unix-based OEM storage products.

SMB 2.1 (2010)

Introduced with Windows Server 2008 R2 and Windows 7 SMB 2.1 brought about a client oplock leasing model that has replaced opportunistic locking to increase caching, enhance performance, and achieve greater energy efficiency. This unlocking procedure enables clients to open files from an SMB server while allowing the system itself to enter sleep mode. In addition, it also supports large maximum transmission unit (MTU).

SMB 3.0 (2012)

Windows 8 and Windows Server 2012 introduced SMB 3.0 which introduced substantial improvements to availability, performance, backup, security, and management with its groundbreaking debut.

MoSMB (2012)

Ryussi Technologies’ proprietary MoSMB implementation is designed for Linux and other Unix-like systems, allowing organizations to take advantage of SMB 2.x and 3.x technology solutions with ease.

SMB 3.02 (2014)

With its inclusion in Windows 8.1 and Windows Server 2012 R2, performance was noticeably improved; additionally, one can now deactivate CIFS/SMB 1.0 support as well as delete any pertinent binaries related to it.

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SMB 3.1.1 (2015)

Released with Windows 10 and Windows Server 2016, SMB 3.1.1 has incorporated advanced encryption, pre-authentication integrity to protect against man-in-the-middle attacks, and cluster dialect fencing for improved security.

What are Ports 139 and 445?

SMB, or Server Message Block protocol, is a file-sharing system that necessitates an exposed port to convey data to other computers. To communicate via this method, ports 139 and 445 are typically used.

Port 139 is essentially a language for devices with Windows operating systems to communicate over NetBIOS. For instance, it enables the communication between printers and serial ports in the form of an application layer network protocol. In other words, Port 139 makes it possible for SMB dialects to transfer data between two entities on a shared network.

Utilizing the TCP stack, the post-Windows 2000 versions of SMB have been explicitly optimized for Port 445 communication over IP addresses. This allows users to access and share files online with ease.

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Are Open Ports Dangerous?

Although ports 139 and 445 are not inherently malicious, there is a risk associated with allowing access to these ports online. To determine if any of your open ports have been compromised, use the netstat command as soon as possible.

The misunderstanding that open ports are vulnerable is an all-too-common misconception. In truth, this perception comes from the general lack of comprehension of how they work, why they exist, and which ones can be left exposed.

Although open ports are a necessity for communication between networks, they can pose an imminent security risk if the service listening to them is vulnerable to exploits or has inadequate network security rules. In such cases, it’s essential that these services be patched and updated regularly in order to minimize threats.

Best Security Practices for Ports 139 and 445 

Here are a few approaches to ensure that ports 139 and 445 stay protected from malicious hackers.

• Avoid the exposure of an SMB Port
• Everything should be patched
• No Single Point of Failure
• Firewall or Endpoint Protection should be used
• A virtual Private Network (VPN) should be used
• Virtual Local Area Networks (VLANs) should be implemented
• MAC Address Filtering should be used

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