What is SMB Port? (A Complete Guide: SMB Port Numbers)

Server Message Block (SMB) is a network protocol that enables devices within the same network to share resources like files, printers, and services. It was previously known as the Common Internet File System (CIFS). SMB facilitates communication between computers over a local network, ensuring seamless access to shared resources.

This local network could be as small as a single office for a small business or as large as a global network connecting multiple offices for a multinational company.

SMB relies on specific SMB ports for communication: Port 135 is used for Microsoft Remote Procedure Call (RPC) to help establish and manage SMB connections. Port 445 is used for direct SMB communication over TCP/IP without requiring older protocols like NetBIOS.

In this article, we will explore what is SMB port and the different SMB port numbers it relies on for efficient resource sharing over networks. In addition, we will explain how smb works on different smb ports.

What is SMB?

The Server Message Block (SMB) protocol is a network communication protocol used to share files, printers, and other resources between devices on the same network. It also offers a way for processes on different computers to communicate securely. Originally developed by IBM in the 1980s with SMB 1.0, the protocol has undergone multiple updates to improve its security, performance, and functionality.

SMB Protocol Dialects Overview 

The Server Message Block (SMB) protocol has evolved through various dialects since its inception, each designed to meet changing network needs and enhance security. Here’s a brief overview of key SMB protocol dialects:

SMB 1.0 (1984)

Developed by IBM for DOS, SMB 1.0 laid the foundation for file and printer sharing across networks. It introduced opportunistic locking (OpLock) to improve performance by enabling client-side data caching. However, its lack of robust security made it vulnerable to exploits, notably the WannaCry ransomware attack in 2017, which highlighted the urgent need to disable SMB 1.0/CIFS to mitigate risks.

Netsmb (2004)

Emerging around 2004, Netsmb represented a crucial update in the SMB protocol, focusing on enhancing security and performance. While specific details are scarce, this dialect aimed to address vulnerabilities in earlier versions, reflecting the growing importance of network security at that time.

SMB 3.02 (2014)

Introduced with Windows 8.1 and Windows Server 2012 R2, SMB 3.02 brought significant improvements in performance and security. It optimized data transmission efficiency and allowed administrators to disable support for the outdated CIFS/SMB 1.0, reducing potential security risks. This version continued the trend of integrating advanced security measures, and enhancing data protection within the SMB framework.

How does SMB Work? 

SMB follows a client-server architecture, where the client sends requests, and the server responds accordingly. This setup makes it easy for devices on the same network to share files and other resources seamlessly, regardless of the operating system—whether it's Windows, Linux, or macOS. 

Once a connection is established, users or applications can send requests to a remote file server, gaining access to resources like mail slots, shared printers, and named pipes. This setup allows users to open, view, edit, move, and update files on the remote server as if they were stored locally.

In earlier versions of Windows, SMB operated on top of the NetBIOS network layer. However, starting with Windows 2000, Microsoft enhanced SMB to run directly over TCP/IP, using a dedicated IP port to improve performance and reliability. Below, we have listed key features of SMB:

1. File Sharing
2. SMB allows multiple users to access shared files over the network, supporting simultaneous use. This is essential in collaborative environments, such as offices, where teams work together on shared documents and projects.
3. Printer Sharing
4. Besides files, SMB enables printer sharing. Users on the same network can send print jobs to a shared printer, making resource management more efficient.
5. Authentication and Authorization
6. SMB includes user authentication mechanisms to ensure that only authorized individuals can access shared resources. This feature enhances network security by controlling access to files and devices.
7. Inter-process Communication
8. SMB also supports communication between processes on different computers, extending its functionality beyond file and printer sharing. It enables network services and applications to interact smoothly.
9. Cross-Platform Compatibility
10. One of SMB’s strengths is its compatibility with various operating systems, allowing different devices to communicate and share resources effectively across diverse environments.

SMB Versions and Updates

The protocol has evolved with newer versions like SMB 2.0, SMB 3.0, and later. These versions introduced encryption for secure data transfers, performance improvements, and support for modern networking needs such as virtualization and cloud storage.

SMB's ongoing development reflects the need to balance usability with security. Its role in file and resource sharing has made it a key element of network infrastructure for businesses of all sizes, ensuring efficient collaboration and secure communication across connected devices.

SMB 2.1

Released with Windows 7 and Windows Server 2008 R2, this version replaced opportunistic locking with a client oplock leasing model to improve caching and performance. It also introduced support for high MTU (Maximum Transmission Unit) and better energy efficiency, allowing clients to enter sleep mode while keeping files open on the server.

SMB 3.0

Introduced in Windows Server 2012 and Windows 8, SMB 3.0 enhanced management, performance, backup capabilities, security, and availability. It became crucial for modern data centers and cloud environments.

SMB 3.02

This version, which debuted with Windows 8.1 and Windows Server 2012 R2, offered performance improvements. It also included an option to disable SMB 1.0/CIFS support, requiring the removal of legacy components to enhance security.

SMB 3.1.1

Released with Windows 10 and Windows Server 2016, this version introduced advanced features like pre-authentication integrity to prevent man-in-the-middle attacks, enhanced encryption, and cluster dialect fencing for improved security in distributed systems.

Knowing which SMB version is in use is important, especially for businesses relying on Windows-based environments. While modern offices rarely use older systems like Windows 95 or XP that rely on SMBv1, some outdated servers may still run these early versions. For optimal performance and security, it’s essential to upgrade to newer SMB versions whenever possible.

What is SMB Port Number? (SMB Port Numbers)

To provide file and print-sharing functions within a network, SMB uses several ports. However, smb ports 139 and 445 are the most often utilized SMB port numbers on a network when using file and print services. But, most users still don’t know what is smb port that you will learn in this section.

Verifying that the ports are open is important to ensure the smooth functioning of SMB on your VPS. To get started with a dependable VPS, consider MonoVM's Linux VPS offerings or their Windows VPS options.

Port 139

SMB dialects that interact over NetBIOS use smb default port 139. It functions as an application layer protocol for device communication across a network in Windows operating systems. For instance, Port 139 is used by printers and serial ports to connect.

Port 445

Simply put, Windows smb port 445 is for file sharing across the network. Microsoft changed Windows 2000 to use port 445 for SMB.

Microsoft-DS also referred to as directory services from Microsoft, uses port 445. Both TCP and UDP protocols use port 445 for several Microsoft services.

Microsoft Active Directory and Domain Services use this port for file replication, user and device authentication, group policies, and trusts.

SMB, CIFS, LSARPC, SMB2, DFSN, NbtSS, SamR, NetLogonR, and SrvSvc protocols and services are most likely involved in the traffic on these ports.

What is SMB Port or SMB Protocol Port? (Samba Port )

In networking, a port serves as a virtual endpoint that manages different types of network connections on the same IP address. This allows multiple services, such as file sharing or printing, to coexist on a single device without conflict.

Samba is a software suite that implements the Server Message Block (SMB) protocol, enabling Unix-like systems (such as Linux) to share files and printers with Windows systems. Samba relies on specific network samba ports, aligning with those used in the SMB/CIFS protocols. Below is an overview of the key samba ports used:

• TCP 139: This port is utilized for SMB communication through NetBIOS over TCP/IP. It allows sharing of files, printers, and other network resources over a local area network (LAN). NetBIOS provides a way for applications on different systems to communicate over the network.
• TCP 445: This port enables direct SMB communication over TCP/IP, bypassing the NetBIOS layer. As a result, it has become the primary port for file sharing, printer access, and inter-process communication, especially in modern networks.
• UDP 137 and 138: These ports handle NetBIOS Name Service (UDP 137) and NetBIOS Datagram Service (UDP 138), respectively. While not directly involved in Samba’s core file-sharing functionality, they support broader SMB-related services in some network setups.

What are the different Variants of the SMB Protocol?

Over time, developers have introduced different SMB dialects to serve various purposes, similar to how languages evolve. One well-known variant is the Common Internet File System (CIFS), which facilitates file sharing. Despite some misconceptions, CIFS and SMB share the same core principles. Here are some of the most notable SMB implementations:

1. CIFS

CIFS is a standard protocol used for file sharing, primarily found on Windows servers and compatible NAS (Network-Attached Storage) devices.

2. Samba

Samba is an open-source implementation of SMB that supports authentication, authorization, name resolution, file and printer sharing, and service announcements. It allows Linux/Unix servers to interact with Windows clients and integrates with Microsoft Active Directory, making it essential for cross-platform environments.

3. NQ (Visuality Systems)

The NQ suite, developed by Visuality Systems, provides portable SMB client and server solutions. It supports the SMB 3.1.1 dialect and can run on non-Windows platforms like Linux, iOS, and Android.

4. MoSMB (Ryussi Technologies)

MoSMB is a proprietary SMB implementation designed by Ryussi Technologies. It is optimized for Linux and other Unix-like systems, making it suitable for specific enterprise environments.

5. Tuxera SMB

This proprietary implementation from Tuxera can operate in either kernel or user space, providing flexibility for various networking environments.

6. Likewise

EMC acquired Likewise in 2012. This software offers multi-protocol file sharing with identity-aware access, providing seamless network file sharing with integrated security features.

What is SMB Authentication?

Like any other network protocol, SMB requires security measures to ensure safe communication. At the user level, SMB authentication involves verifying a username and password to grant access to a server's resources.

A system administrator manages access by adding or removing users and monitoring permissions. To access a shared file or server, users typically provide a one-time password at the share level. However, this method does not require identity verification, focusing only on access to the specific shared resource.

Is SMB Safe?

Is it safe to use SMB? Generally, it appears to be secure for now, but new vulnerabilities can emerge at any time. To protect your system from potential threats, it's advisable to disable SMB entirely if you don't have any applications relying on it.

As of October 2017, SMB is not enabled by default in Windows 10, so you only need to take precautions if you're using an older version of Windows.

What Actions Should You Take to Ensure the Security of Your SMB Port?

To ensure the security of your SMB port, the following measures should be taken:

Avoid Exposing SMB Ports

For over a decade, opening ports 135 through 139 and 445 has been considered unsafe. While exposing ports 139 and 445 to the Internet isn't inherently dangerous, there are several recognized risks associated with it.

To check if a port is open, you can use the netstat command.

Patch Vulnerabilities

Regularly update your systems to guard against threats such as Man-in-the-Middle (MITM) attacks and NetBIOS Name Service (NBNS) spoofing.

Eliminate Single Points of Failure

To ensure data security, maintain at least one additional secure backup location, as risks can arise from malware, hardware failures, or database issues.

Utilize Firewalls and Endpoint Security

Effective security solutions typically include a blacklist of known malicious IP addresses and their most frequently used ports. Want to learn more about IP addresses? Check out our detailed articles for a deeper understanding!

Implement a Virtual Private Network (VPN)

VPNs encrypt and safeguard your network traffic. Looking to boost your online privacy? Explore our comprehensive guide on "What is a VPN? How Does a VPN Work?" to learn how to enhance your digital security!

Use VLANs

In business environments, utilizing Virtual Local Area Networks (VLANs) can help segregate internal traffic according to specific requirements. This practice is crucial for preventing lateral movement and privilege escalation attacks.

Employ MAC Address Filtering

This method helps block unauthorized devices from accessing your network. The strategies mentioned above are common ways to prevent malicious entities from exploiting vulnerabilities in SMB.

However, this list is not exhaustive, as attackers employ various tactics, including masquerading as legitimate assets on compromised employee workstations.

Therefore, a proactive cybersecurity strategy is essential for organizational security. This approach should be grounded in strong fundamentals, incorporating a defence-in-depth methodology, layered architecture adhering to the principle of least privilege, and a collaborative effort involving people, processes, and technology.

Are Open SMB Ports Dangerous? (SMB Ports)

The idea that open ports are inherently dangerous often stems from misunderstandings about their function and potential vulnerabilities. Here’s a clearer perspective on the safety of open ports:

• Understanding Open SMB Ports

Open ports are essential for network communication, acting as gateways that allow services and applications to communicate across networks.

• Not Inherently Dangerous

Open ports themselves do not pose an inherent risk; rather, the danger lies in how well the services or applications running on those ports are configured and secured.

• Factors Determining Safety

The safety of open ports is influenced by several factors:

• Service Configuration: Proper configuration is crucial for preventing vulnerabilities.
• Software Updates: Using outdated software can leave services exposed to risks.
• Security Measures: Adequate security protections must be in place to mitigate potential threats.
• Real-World Example

A notable illustration of the risks associated with open ports is the exploitation of certain SMB default ports during the WannaCry ransomware attack. In this case, the danger was not simply due to the open ports, but rather vulnerabilities in the SMB services that were exploited by the EternalBlue exploit.

Conclusion

We have learned about what is smb port and smb port numbers. We explored how the Server Message Block (SMB) protocol facilitates inter-process communication and allows programs and services on networked computers to interact seamlessly. SMB ports support various essential network functions, including file and printer sharing, as well as access to devices.

In essence, SMB enables applications on a computer to read and write files and request services from server software across a network.

As computers increasingly connect over the internet for resource sharing, it's crucial to remain vigilant against potential attacks from malicious users.

Exposed SMB ports on Windows servers present a tempting target for attackers, potentially granting them unauthorized access to specific systems or corporate networks. However, SMB administrators can implement several straightforward strategies to reduce the risks and vulnerabilities associated with SMB ports against internet threats.

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