What is SMB? Explaining the Server Message Block Protocol

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If you follow tech news, you might have heard about the global cyberattacks that exploited an SMB vulnerability. You may not have heard of SMB or Server Message Block before, but if you're a Windows user, you've been using it. So, if this has got you worried about the security of your Windows system and wondering “What is SMB?” and how safe it is, read on.

What is the SMB Protocol?

SMB (Server Message Block) or Server Message Block is a communication protocol that employs a client-server model for sharing files, resources, and communications over a network. It enables connected systems to remotely open, edit, share, or print files across a network. The SMB protocol was designed to facilitate easy and secure file sharing among users within a local area network. Its purpose is to supersede earlier file-sharing protocols like CIFS and NFS in Windows systems.

How does SMB work?

Server Message Block (SMB) Protocol follows a client-server architecture for communication over a network. The server has files or resources that can be shared with other computers on the network, referred to as clients, upon request. SMB is also known as a request-response protocol because the client initiates a connection by sending an SMB request. The server responds with an SMB reply, establishing a bidirectional communication channel for resource or file sharing after confirmation.

SMB operates mainly at the Application Layer of a network and directly relies on TCP/IP or other networking protocols. There are four main components in an SMB operation: the SMB Server, the SMB Client, the SMB Share, and the SMB Port. The system where the resource is located is called the SMB Server, while the requesting system is called the SMB Client. The resource to be shared is referred to as the SMB Share, and the port where it runs is called the SMB Port.

[[[TOP]]](#part0) ### SMB Protocol Version Development

The Server Message Block (SMB) protocol was initially developed by IBM in 1983 and later adopted by Microsoft for use in their Windows operating systems. In response to new challenges, the protocol has gone through multiple evolutions and revisions. Different versions of the SMB protocol are referred to as "dialects." Here's a brief overview of some key dialects: 1. **SMB 1.0/CIFS**: The original SMB protocol, also known as Common Internet File System (CIFS), was widely used but is now considered outdated due to security concerns. It was the primary dialect for file sharing in Windows systems until the introduction of newer versions. 2. **SMB 2.0**: Introduced in 2007 with Windows Server 2008 and Windows Vista, SMB 2.0 aimed to improve performance, reduce latency, and add features such as directory change notifications. It introduced significant changes compared to SMB 1.0, including a more efficient packet format. 3. **SMB 2.1**: Released in 2009 with Windows 7 and Windows Server 2008 R2, this dialect focused on further performance enhancements and support for larger files. It also introduced support for multi-channel connectivity, allowing for better fault tolerance. 4. **SMB 3.0**: Debuted in 2012 with Windows 8 and Windows Server 2012, SMB 3.0 brought numerous improvements, including support for server-side caching, encryption, and disaster recovery. It also introduced concurrent connections to different volumes, making it more suitable for clustered environments. 5. **SMB 3.0.2**: A minor update to SMB 3.0, released with Windows Server 2012 R2, which addressed some bugs and improved performance. 6. **SMB 3.1.1**: This dialect, introduced with Windows 10 and Windows Server 2016, added support for AES-128 encryption, improved performance, and added new features like SMB Direct (SMB over RDMA) for low-latency, high-bandwidth network communication. It's worth noting that Microsoft has been pushing for the retirement of SMB 1.0 due to its inherent security vulnerabilities. Most modern systems and applications now default to using SMB 3.x dialects for file sharing and related tasks.

1. SMB 1.0: Server Message Block 1.0, a file sharing protocol commonly used in network communication within Windows operating systems.

This is the original version of SMB that IBM introduced for DOS systems in 1984. SMB 1.0 came with Oplock functionality and ran on top of NetBIOS and TCP/IP interfaces, but it had its issues, such as lack of encryption, excessive chatter, and poor security.

2. SMB 2.0 (Server Message Block 2.0)

With the release of Windows Vista in 2006, SMB 2.0 was introduced. It was a significant improvement over SMB 1.0, with added features such as reduced commands and messages for decreased communication complexity, support for WAN acceleration, and pre-authentication integrity. Unlike SMB 1.0, which used 16-bit data sizes, it utilized 32-bit or 64-bit data sizes.

3. SMB 2.1

SMB 2.1 was introduced with Windows 7 and Windows Server 2008 R2 in 2010. It offered minor improvements over SMB 2.0, particularly in Oplock (Opportunistic Locking) functionality for enhanced caching and performance. This version of SMB also added support for Maximum Transmission Units (MTU) and improved power-saving modes.

4. SMB 3.0 (Server Message Block 3.0)

In 2012, with the release of Windows 8 and Windows Server 2012, SMB 3.0 was introduced. This was a major update to the protocol, introducing end-to-end encryption and many other features such as SMB Direct, SMB Multichannel, and support for Remote Volume Shadow Copy Service, among others. These enhancements significantly improved SMB's performance, security, manageability, availability, and backup capabilities.

5. SMB 3.02 (Server Message Block 3.02)

SMB 3.0.2 was introduced in 2014 with Windows 8.1 and Windows Server 2012 R2, primarily to address vulnerabilities in SMB 1.0. It allows users to completely disable SMB 1.0 on their systems, enhancing security and improving SMB performance.

6. SMB 3.1.1 Protocol

The latest major dialect of SMB is SMB 3.1.1, which was released in 2015 alongside Windows 10 and Windows Server 2016. This version introduced features such as the use of AES-128 encryption, directory caching, improved protection against man-in-the-middle attacks, and cluster dialect fencing. The most recent operating system, Windows 11, also utilizes the SMB 3.1.1 dialect with additional enhancements.

Differences Between SMB and CIFS

CIFS, or Common Internet File System, is a version or dialect of SMB (Server Message Block) introduced by Microsoft in 1996 with Windows 95. It's an improved version of SMB 1.0, but since then, several more enhanced and secure versions of SMB have been released. The table below explains the significant differences between SMB and CIFS.

Frequently Asked Questions (FAQ) for Small and Medium-sized Businesses (SMBs)

We've covered all the important details about what SMB is, how it works, and its different versions. If you have more questions about SMB, check out the FAQ section below where we answer the most common queries about SMB found on the internet.

1. Is the Server Message Block (SMB) protocol still in use?

Yes, the latest Windows 11 operating system still employs SMB (Server Message Block) for network file transfer. It utilizes the most recent version of the SMB protocol, which is SMB 3.1.1, featuring enhancements such as AES-256 encryption and support for encrypted SMB Direct.

2. Is SMB secure?

Yes, the latest versions of SMB are highly secure and resistant to malware attacks. Older versions like SMB 1.0 and CIFS, on the other hand, are vulnerable to network breaches and should be removed from your system.

The Server Message Block (SMB) protocol typically uses the following ports: - TCP 445: This is the primary port for SMBv2 and SMBv3. - UDP 137 and 138: These ports are used for NetBIOS (Network Basic Input/Output System) name resolution, which is part of SMBv1 but not mandatory. It's worth noting that SMBv1 has been deprecated due to security concerns, and most modern systems use SMBv2 or SMBv3.

The Server Message Block (SMB) protocol requires an open port to transmit files over a network. Currently, SMB uses port 445 since it runs directly over TCP/IP. Older versions used ports 137, 138, and 139.

SMB (Server Message Block) and FTP (File Transfer Protocol) are both protocols used for file sharing and transfer, but they have some distinct advantages: 1. **Integration**: SMB is more tightly integrated into the Windows operating system, making it easier to share files and printers in Windows network environments. In contrast, FTP requires dedicated server software to run. 2. **Security**: SMB supports various security protocols such as NTLM, Kerberos, and SSL/TLS, providing authentication and data encryption. FTP, without additional security extensions like FTPS or SFTP, can be less secure during data transfer. 3. **Permission Management**: SMB offers more granular permission control, allowing administrators to assign specific access rights to users, like read, write, and execute. FTP typically has basic read/write access control. 4. **Resume Transfer**: While FTP supports resuming interrupted transfers, this requires support from both the server and client. SMB usually doesn't need this feature since it typically operates in continuous network environments. 5. **Network Efficiency**: SMB optimizes performance over the network with features like caching and reduced network communication. FTP is simpler and might require more network roundtrips. 6. **Multi-Session Handling**: SMB supports multiple concurrent sessions, enabling users to handle multiple files or operations simultaneously. FTP generally handles one file transfer at a time. In summary, SMB provides a more comprehensive, secure, and efficient file-sharing experience in Windows environments, while FTP serves as a more general, cross-platform file transfer solution.

SMB (Server Message Block) and FTP (File Transfer Protocol) are protocols used for transferring files over a network. SMB is relatively simpler and more user-friendly compared to FTP. In addition to file transfer, SMB also allows the sharing of resources such as printers, which FTP does not support. Within a local network, SMB is the preferred choice for file transfers and resource sharing. When it comes to transferring files across the internet, FTP becomes a better option.

Conclusion

System security is crucial, as it often contains your important and sensitive data. Cyberattacks, particularly ransomware, are on the rise. It's essential to keep a close eye on the software and processes running on your system to ensure they don't pose a security risk. If you're using an older version of MSB, it's recommended to disable or uninstall it immediately to safeguard your system.