Written by Christian Ahmer | 11/19/2023

Server Message Block (SMB)

Server Message Block (SMB) is a network communication protocol designed for sharing access to files, printers, serial ports, and other resources on a network. It was originally designed by IBM and has been adopted and extended by Microsoft. SMB is most commonly used in Windows operating systems, where it forms the basis of Windows file and printer sharing.

Key Aspects of SMB

  • File and Printer Sharing: SMB allows users to share files and printers with other network users. It can also handle more complex interactions like file locking and conflict resolution.

  • Network Browsing: The protocol supports the discovery of network devices and resources, enabling users to see the available computers, printers, and files on the network.

  • Authentication and Authorization: SMB provides a mechanism for user authentication and access control to resources.

  • Opportunistic Locking: It supports an efficiency mechanism known as opportunistic locking (oplocks), which allows a client to lock a file and cache data locally to improve performance.

Versions of SMB

  • SMB 1.0 (SMB1): The original version, which became widely used but is now considered outdated and insecure.

  • SMB 2.0: Introduced with Windows Vista and Windows Server 2008, it improved performance, had better error handling, and supported event-driven architecture.

  • SMB 2.1: Released with Windows 7 and Windows Server 2008 R2, adding minor improvements over SMB 2.0.

  • SMB 3.0: Introduced with Windows 8 and Windows Server 2012, adding significant new features, including end-to-end encryption, improved performance, and better fault tolerance.

  • SMB 3.1.1: Included with Windows 10 and Windows Server 2016, further improving security with pre-authentication integrity to prevent man-in-the-middle attacks.

SMB in Non-Windows Systems

While SMB is most commonly associated with Windows, it is also used in other operating systems:

  • Samba: An open-source implementation of the SMB protocol found in Unix-like systems such as Linux. It allows these systems to interact with Windows clients and servers.

  • macOS: Apple’s operating systems have included support for SMB for file sharing with Windows systems.

Security Considerations

Historically, SMB has had vulnerabilities that were exploited by malware, most notably the WannaCry ransomware attack that took advantage of the SMBv1 protocol. As a result, SMBv1 is generally disabled by default in modern systems, and the use of newer versions with better security features is recommended.

SMB and Modern Networks

SMB continues to evolve to meet the needs of modern networked environments. It is a versatile and integral protocol for enterprise environments where file and resource sharing is necessary. Given its widespread use, knowledge of SMB configuration and security is important for network administrators to ensure seamless and secure operations across networked devices.