Номер порта smb windows

Organizations are increasing their use of various solutions to address communication needs across their infrastructure. As file systems are an integral part of collaboration, this article will dive into one of the most widely used protocols necessary for many systems. We will learn more about the SMB protocol, Port 139, Port 445, how it works, the risks associated with it, and remediation steps to provide a more secure communication channel.

What is SMB Port?

The SMB (Server Message Block) port is a network port primarily utilized for file and resource sharing across a computer network. SMB operates over TCP port 445 and enables shared access to files, printers, and serial ports among devices on a network.

Moreover, its core function of resource sharing, enables SMB to be utilized for following use cases:

• Involving mail slots (inter-process communication mechanisms)
• Named pipes (a method for processes to communicate either on the same machine or over a network).

What are Port 139 and Port 445?

For the SMB protocol to function correctly, network ports are required to communicate with other systems. SMB requires either port 139 or port 445 to be an open port.

Port 139

Originally, SMB ran on port 139 as an application layer protocol for Windows computers to communicate with each other on the same network. It was run on NetBIOS over TCP/IP and is being passed over by port 445 in modern environments.

Port 445

Port 445 port is used by newer versions of SMB as Windows 2000 adopted it for use for direct TCP/IP communication. Generally favored over port 139, it also allows for communication across different networks for things like internet-based file sharing.

How does SMB Protocol work?

Client-Server Communication

SMB is known as a response-request protocol. It uses the approach of a client-server relationship, where the client makes any specific request, and the server responds as requested. Some examples of practical use today are situations where file resources are requested or printers need to be shared. SMB is also used for other uses, such as mail slots and named pipe situations.

Historical Development

Historically, SMB originated with IBM and was designed in 1983 for DOS file access over networks. It wasn’t until 1990 that Microsoft merged the SMB protocol with its LAN Manager product. From there, continual maturation of the SMB protocol appeared in instances such as the introduction of CIFS, as well as milestone improvements in efficiency, performance, and security, as described through the aforementioned upgrades of SMB 2 and SMB 3.

SMB Protocol Dialects

With an increasing presence of SMB implementations across the industry, network requirements evolved to have different demands of SMB. This led to the emergence of different SMB protocol dialects to cater to different environments. Depending on the need and use, different dialects could be implemented for a variety of purposes.

SMB Dialect Variations

Here’s a list of popular SMB dialects along with their uses:

• CIFS (Common Internet File System): was a Microsoft developed dialect debuting in Windows 95 that was designed for network connections over remote servers. This dialect (CIFS Port) enabled clients to connect to remote file and printer shares as if they were accessed locally.

• Samba: Samba is an open source dialect (Samba port) that enables Linux/Unix machines to communicate with Windows devices.

• NQ: was developed by Visuality Systems that brings the SMB protocol to non-Windows platforms. Especially prevalent in devices such as printers and home network devices.

• Tuxera SMB and MoSMB: Dialects were also created as proprietary methods using the SMB protocol for specific features, such as enterprise file sharing and advanced authentication.

Security Risks Associated with Open SMB Ports

Ports like the ones used with the SMB protocol are necessary to communicate from within and across different networks. While their use isn’t itself dangerous, open ports can be used and exploited for malicious purposes.

Having over exposed ports can lead to the following vulnerabilities, such as:

• A Wormable port
• Man-In-The-Middle attacks,
• NetBIOS spoofing,

Case Study: WannaCry Ransomware:

Once recent occurrence was the WannaCry ransomware attack that targeted Windows clients running an outdated version of SMB. A worm infection was installed on a target machine, encrypting the user’s files in exchange for ransom. In addition to that, the infected system would also start searching for other machines via the SMB v1 protocol, and if other systems were using those open ports, they would be susceptible to the ransomware self-install on that machine and continue its spread.

While WannaCry created havoc and pain for many companies and networks, its disastrous results could have been much less impactful had systems been patched with up-to-date security measures.

Best Practices to Secure SMB Ports 139 and 445

Since SMB ports can be targeted, here are some best practices to implement to protect against various attacks:

Enable Firewall and Endpoint Protection

Enabling these network security devices can protect these ports from threats as well provide blacklisting services against known malicious IP addresses.

Utilize VPNs

By utilizing VPNs, network traffic can be encrypted and protected against malicious actors.

Create VLANs

Creating Virtual LANs can be utilized to isolate internal traffic to limit attack surface.

Implement MAC Address Filtering:

These filters can keep unknown systems from accessing and infiltrating your internal network.

Implement System Configuration Changes

Following changes can be made to harden your security against SMB attacks:

Disable NetBIOS over TCP/IP

• Select Start, point to Settings, and then select Network and Dial-up Connection.
• Right-click Local Area Connection, and then select Properties.
• Select Internet Protocol (TCP/IP), and then select Properties.
• Select Advanced.
• Select the WINS tab, and then select Disable NetBIOS over TCP/IP.

Commands to monitor port status

To determine if NetBIOS is enabled on a Windows computer, run a net config redirector or net config server command to see if if any ‘NetBT_Tcpip’ device is bound to the network adapter.

Conclusion

The SMB protocol has proved to be a valuable and vital method of accessing different network resources. While it has enabled things like file sharing and connectivity, security measures should be taken to ensure authorized access within the network. Securing ports and keeping up to date with protocols are a couple of examples of how to heighten your security profile in modern-day networking.

In conjunction with network security, Netwrix can fulfill your security plan at the data layer. With Netwrix solutions, we can help your organization see who has access to your data and the activity that surrounds it. Monitoring is a critical part of detecting attacks and protecting against breaches.

Картинка с сайта: blog.netwrix.com

Introduction to SMB (Server Message Block)

Server Message Block (SMB) is a widely used network protocol that allows shared access to files, printers, and serial ports between nodes on a network. It’s heavily used in Windows environments but also supported on Linux and macOS.Understanding which port SMB uses is crucial for configuring firewalls, enhancing security, and enabling successful network file sharing.

What is the Default Port for SMB?

The default port used by SMB is TCP 445. This enables direct communication without relying on older NetBIOS services. Previously, SMB also ran over TCP 139 through NetBIOS, but this method is now mostly deprecated.

Port 445: SMB over TCP

Port 445 supports SMB directly over TCP/IP and is used by modern operating systems. It eliminates the dependency on NetBIOS, simplifying configuration and increasing security.

Port 139: NetBIOS Session Service

Port 139 is associated with older SMB implementations using NetBIOS over TCP/IP. Although some legacy systems may still use it, it’s considered less secure and should be disabled if possible.

Why Does SMB Use Port 445?

Modern SMB versions (SMBv2 and SMBv3) require port 445 to establish secure and efficient communication. Port 445 supports authentication, encryption, and direct connection between devices without relying on name resolution services.

TCP vs UDP for SMB Communication

SMB primarily uses TCP for data transfer. However, NetBIOS services historically required UDP for name resolution and datagram services.

Does SMB Use Both Ports 445 and 139?

Most modern environments use only port 445, but older systems may still use both ports 445 and 139. Ensuring your infrastructure is up-to-date helps simplify this and boosts security.

Disable SMBv1 using PowerShell:

Set-SmbServerConfiguration -EnableSMB1Protocol $false

SMB Ports and Security: Why Blocking Port 445 Matters

The WannaCry and NotPetya ransomware attacks exploited vulnerabilities in SMBv1 over port 445. Blocking or monitoring this port can protect your infrastructure from similar attacks.

Key Tips:

Block port 445 at the perimeter firewall

Disable SMBv1 on all devices

Use Endpoint Detection & Response (EDR) for monitoring SMB usage.

Best Practices: Firewall Rules for SMB

Windows

New-NetFirewallRule -DisplayName "Block SMB 445" -Direction Inbound -LocalPort 445 -Protocol TCP -Action Block

Linux (UFW)

sudo ufw deny 445/tcpsudo ufw deny 139/tcp

How to Open SMB Ports on Windows and Linux

To enable SMB for internal file sharing:On Windows:

Go to Windows Firewall > Advanced Settings. Create a new inbound rule for TCP 445.

Allow access from trusted IP ranges only.

On Linux:

sudo ufw allow from 192.168.0.0/16 to any port 445 proto tcp

Alternatives to SMB fo

SFTP (SSH File Transfer Protocol)

NFS (Network File System)

WebDAVCloud-based sharing (e.g., OneDrive, Google Drive)

These options offer encryption, centralized access control, and better protection for remote sharing.

Conclusion: Proactive SMB Port Security

Understanding the role of ports 445 and 139 is essential for secure SMB implementation. Modern networks should rely exclusively on TCP port 445, with legacy ports disabled. Firewalls must be configured to restrict external access and reduce risk from exploits.

The server message block (SMB) protocol provides “client-server communication,” which allows programs and services on networked computers to communicate with one another. SMB enables network functions like file, print and device sharing, among others.

What Is an SMB Port?

A server message block (SMB) port is a network port that allows devices within the same network to communicate with each other, so they can exchange files and share data, printers and other resources. In the case of files, users on different devices can perform various actions like opening, editing and moving files. While SMB ports have relied on different protocols through the years, they currently use port 445 (more on this to come).  

How Does SMB Work?

The SMB protocol sends and receives request-response messages to establish communication between clients and servers. This arrangement sets up a file-sharing system as if a user were accessing data on their hard drive. It makes dealing with networked systems all over the world a lot easier.

Other operating systems, such as Unix, Linux and OS/2, use Samba to connect and provide file-sharing services within a network by speaking the same language as SMB.

SMB History and Evolution

During the mid-1990s, Microsoft incorporated SMB in their LAN Manager product, which IBM initially built. SMB 1.0 was renamed common internet file system (CIFS) , and Microsoft published draft standards to the Internet Engineering Task Force (IETF), though these have now expired.

SMB and early CIFS implementation had a number of flaws that limited its applicability to managing small files for end-users. The protocol was “chatty,” which resulted in poor performance over long distances or when there was a lag between client and server. Around this time, the Samba project was born, with the goal of reverse-engineering the SMB/CIFS protocol and developing an SMB server that would allow MS-DOS clients to access files on Unix machines. 

SMB has gone through a few evolutions since then. 

SMB 2.0

Microsoft released SMB2 with Windows Vista in 2006. SMB2.0 had a significant number of improvements over SMB 1.0, particularly reducing the “chattiness” of the protocol by reducing the number of commands and subcommands from hundreds to 19.

The term CIFS becomes redundant, as it only applied to SMB version 1.0.

SMB2 supported many other improvements like TCP window scaling and WAN acceleration, opportunistic locking and a feature known as “pipelining” to enable multiple requests to be queued at the same time.

Performance improvements included allowing larger block sizes, which improved large file transfers. Microsoft introduced “durable file handles” that allowed the connection to an SMB server to survive brief network failures frequently seen in wireless networks. They did this by allowing clients to transparently reconnect to servers. 

SMB 2.1

SMB 2.1 was released alongside Windows 7 and Windows Server 2008, and included minor upgrades. 

SMB 3.0

With Windows 8 and Windows Server 2012, SMB 3.0 (also known as SMB 2.2) was released. SMB3 included significant protocol modifications such as the SMB Direct Protocol (SMB over remote direct memory access (RDMA) and SMB Multichannel (many connections per SMB session), which are meant to improve SMB2 performance, particularly in virtualized data centers.

SMB 3.1.1

SMB 3.1.1 was introduced alongside Windows Server 2016 and Windows 10. The protocol comes with additional security measures, including advanced encryption, expanded caching options and pre-authentication features to address man-in-the-middle attacks.  

SMB Protocol Ports

To provide file and print-sharing services within a network, SMB uses a number of ports. The following are all known SMB v2/v3 ports:

• TCP 445 — SMB over transmission control protocol (TCP) without the need for a network basic input/output system (NetBIOS).
• UDP 137 — SMB over user datagram protocol (UDP or Name Services).
• UDP 138 — SMB over UDP (datagram).
• TCP 139 — SMB over TCP (session service).

More on CybersecurityWhat Is Smishing

SMB Ports 139 and 445 Explained

There are two common ports you will see in SMBs — Port 139 and Port 445. Here’s what they do.

Port 139

Port 139 is used by the NetBIOS session service. Prior to Windows 2000, most operating systems used TCP 139, with SMB running on top of NetBIOS. NetBIOS is a service on the Open Systems Interconnection (OSI) model’s session layer that allows applications to communicate with one another within a local area network (LAN). This might be anyone on the internet, but because of security concerns, it’s not a recommended alternative.

Port 445

Windows uses port 445 for file sharing across the network. From Windows 2000 onward, Microsoft changed SMB to use port 445. Microsoft directory services, often known as Microsoft-DS, use port 445.

TCP and UDP protocols both use port 445 for numerous Microsoft services. For file replication, user and computer authentication, group policy and trusts, Microsoft Active Directory and Domain Services use this port. SMB, CIFS, SMB2, DFSN, LSARPC, NbtSS, NetLogonR, SamR and SrvSvc protocols and services are most likely to be found on these ports.

Is SMB Secure?

While different versions of SMB provide varying levels of security and protection, SMBv1 was discovered to have a vulnerability that hackers may exploit to execute their code without the user’s knowledge. When a device becomes infected, it attacks other devices that are linked to it. The National Security Agency (NSA) uncovered the flaw in 2017.

The exploit was called EternalBlue, and it was taken from the NSA and posted online by the Shadow Brokers hacker group. Microsoft did issue a patch to address the vulnerability, but the WannaCry ransomware attack hit the world just a month later.

More recently, LemonDuck malware has taken advantage of EternalBlue and launched brute-force attacks on SMB services to gain network access. Meanwhile, hackers used DarkGate malware to spread their malware via Samba file shares in a brief campaign. SMB security has improved over the years, but the protocol isn’t immune to attacks — especially as malicious players invent new methods for infiltrating SMB services.

 More on Cybersecurity: What Is a Phishing Attack? (With 18 Examples)

How to Prevent SMB Vulnerabilities

To keep your SMB services secure, combine the following tools and best practices for shoring up your defenses against SMB attacks.  

Patch All Devices 

Attackers will be unable to access a patched machine, but a huge number of Windows computers have yet to be patched. The March 2017 update from Microsoft can assist in patching the server message block vulnerabilities. If you use a Windows 10 or later system, the fixes are already built in. This is why most SMB assaults target Windows 7 and earlier. Furthermore, the WannaCry patch can prevent EternalBlue exploits and similar flaws. 

Practice Healthy SMB Habits 

It’s better to have layers of security when it comes to protecting yourself from cyberattacks, as it is with other things. Apart from the WannaCry and ransomware patches, you can further safeguard your systems by restricting SMB access from the internet, blocking SMB in offsite computers when in public areas and removing SMB if it’s not needed.

Establish Firewall and Endpoint Protection Measures

Firewalls are excellent tools for regulating network traffic, ensuring only authorized users can access network information. For any devices that fall outside firewalls, endpoint protection methods like antivirus software can shield laptops, phones and other devices from the initial attempts of cyber attackers. 

Invest in Detection Tools and Services

Finally, vulnerability scanning and managed detection and response services can help your system avoid and identify SMB attacks and other cyberattacks.

Server Message Block (SMB) is a communication protocol^[1] used to share files, printers, serial ports, and miscellaneous communications between nodes on a network. On Microsoft Windows, the SMB implementation consists of two vaguely named Windows services: «Server» (ID: LanmanServer) and «Workstation» (ID: LanmanWorkstation).^[2] It uses NTLM or Kerberos protocols for user authentication. It also provides an authenticated inter-process communication (IPC) mechanism.

SMB was originally developed in 1983 by Barry A. Feigenbaum at IBM^[3] to share access to files and printers across a network of systems running IBM’s IBM PC DOS. In 1987, Microsoft and 3Com implemented SMB in LAN Manager for OS/2, at which time SMB used the NetBIOS service atop the NetBIOS Frames protocol as its underlying transport. Later, Microsoft implemented SMB in Windows NT 3.1 and has been updating it ever since, adapting it to work with newer underlying transports: TCP/IP and NetBT. SMB over QUIC was introduced in Windows Server 2022.

In 1996, Microsoft published a version of SMB 1.0^[4] with minor modifications under the Common Internet File System (CIFS ) moniker. CIFS was compatible with even the earliest incarnation of SMB, including LAN Manager’s.^[4] It supports symbolic links, hard links, and larger file size, but none of the features of SMB 2.0 and later.^[4][5] Microsoft’s proposal, however, remained an Internet Draft and never achieved standard status.^[6] Microsoft has since discontinued the CIFS moniker but continues developing SMB and publishing subsequent specifications. Samba is a free software reimplementation of the SMB protocol and the Microsoft extensions to it.

Server Message Block (SMB) enables file sharing, printer sharing, network browsing, and inter-process communication (through named pipes) over a computer network. SMB serves as the basis for Microsoft’s Distributed File System implementation.

SMB relies on the TCP and IP protocols for transport. This combination allows file sharing over complex, interconnected networks, including the public Internet. The SMB server component uses TCP port 445. SMB originally operated on NetBIOS over IEEE 802.2 — NetBIOS Frames or NBF — and over IPX/SPX, and later on NetBIOS over TCP/IP (NetBT), but Microsoft has since deprecated these protocols. On NetBT, the server component uses three TCP or UDP ports: 137 (NETBIOS Name Service), 138 (NETBIOS Datagram Service), and 139 (NETBIOS Session Service).

In Microsoft Windows, two vaguely named Windows services implement SMB. The «Server» service (ID: LanmanServer) is in charge of serving shared resources. The «Workstation» service (ID: LanmanWorkstation) maintains the computer name and helps access shared resources on other computers.^[2] SMB uses the Kerberos protocol to authenticate users against Active Directory on Windows domain networks. On simpler, peer-to-peer networks, SMB uses the NTLM protocol.

Windows NT 4.0 SP3 and later can digitally sign SMB messages to prevent some man-in-the-middle attacks.^[7][8][9] SMB signing may be configured individually for incoming SMB connections (by the «LanmanServer» service) and outgoing SMB connections (by the «LanmanWorkstation» service). The default setting for Windows domain controllers running Windows Server 2003 and later is to not allow unsigned incoming connections.^[10] As such, earlier versions of Windows that do not support SMB signing from the get-go (including Windows 9x) cannot connect to a Windows Server 2003 domain controller.^[8]

SMB supports opportunistic locking (see below) on files in order to improve performance. Opportunistic locking support has changed with each Windows Server release.

In the SMB protocol, opportunistic locking is a mechanism designed to improve performance by controlling caching of network files by the client.^[11] Unlike traditional locks, opportunistic lock (OpLocks) are not strictly file locking or used to provide mutual exclusion.

There are four types of opportunistic locks.

Batch Locks

Batch OpLocks were created originally to support a particular behavior of DOS batch file execution operation in which the file is opened and closed many times in a short period, which is a performance problem. To solve this, a client may ask for an OpLock of type «batch». In this case, the client delays sending the close request and if a subsequent open request is given, the two requests cancel each other.^[12]

Level-1 OpLocks / Exclusive Locks

When an application opens in «shared mode» a file hosted on an SMB server which is not opened by any other process (or other clients) the client receives an exclusive OpLock from the server. This means that the client may now assume that it is the only process with access to this particular file, and the client may now cache all changes to the file before committing it to the server. This is a performance improvement, since fewer round-trips are required in order to read and write to the file. If another client/process tries to open the same file, the server sends a message to the client (called a break or revocation) which invalidates the exclusive lock previously given to the client. The client then flushes all changes to the file.

Level-2 OpLocks

If an exclusive OpLock is held by a client and a locked file is opened by a third party, the client has to relinquish its exclusive OpLock to allow the other client’s write/read access. A client may then receive a «Level 2 OpLock» from the server. A Level 2 OpLock allows the caching of read requests but excludes write caching.

Filter OpLocks

Added in Windows NT 4.0, Filter Oplocks are similar to Level 2 OpLocks but prevent sharing-mode violations between file open and lock reception. Microsoft advises use of Filter OpLocks only where it is important to allow multiple readers and Level 2 OpLocks in other circumstances. Clients holding an OpLock do not really hold a lock on the file, instead they are notified via a break when another client wants to access the file in a way inconsistent with their lock. The other client’s request is held up while the break is being processed.

Breaks

In contrast with the SMB protocol’s «standard» behavior, a break request may be sent from server to client. It informs the client that an OpLock is no longer valid. This happens, for example, when another client wishes to open a file in a way that invalidates the OpLock. The first client is then sent an OpLock break and required to send all its local changes (in case of batch or exclusive OpLocks), if any, and acknowledge the OpLock break. Upon this acknowledgment the server can reply to the second client in a consistent manner.

The use of the SMB protocol has often correlated with a significant increase in broadcast traffic on a network. However the SMB itself does not use broadcasts—the broadcast problems commonly associated with SMB actually originate with the NetBIOS service location protocol.^{[clarification needed]} By default, a Microsoft Windows NT 4.0 server used NetBIOS to advertise and locate services. NetBIOS functions by broadcasting services available on a particular host at regular intervals. While this usually makes for an acceptable default in a network with a smaller number of hosts, increased broadcast traffic can cause problems as the number of hosts on the network increases. The implementation of name resolution infrastructure in the form of Windows Internet Naming Service (WINS) or Domain Name System (DNS) resolves this problem. WINS was a proprietary implementation used with Windows NT 4.0 networks, but brought about its own issues and complexities in the design and maintenance of a Microsoft network.

Since the release of Windows 2000, the use of WINS for name resolution has been deprecated by Microsoft, with hierarchical Dynamic DNS now configured as the default name resolution protocol for all Windows operating systems. Resolution of (short) NetBIOS names by DNS requires that a DNS client expand short names, usually by appending a connection-specific DNS suffix to its DNS lookup queries. WINS can still be configured on clients as a secondary name resolution protocol for interoperability with legacy Windows environments and applications. Further, Microsoft DNS servers can forward name resolution requests to legacy WINS servers in order to support name resolution integration with legacy (pre-Windows 2000) environments that do not support DNS.

Network designers have found that latency has a significant impact on the performance of the SMB 1.0 protocol, that it performs more poorly than other protocols like FTP. Monitoring reveals a high degree of «chattiness» and a disregard of network latency between hosts.^[13] For example, a VPN connection over the Internet will often introduce network latency. Microsoft has explained that performance issues come about primarily because SMB 1.0 is a block-level rather than a streaming protocol, that was originally designed for small LANs; it has a block size that is limited to 64K, SMB signing creates an additional overhead and the TCP window size is not optimized for WAN links.^[14] Solutions to this problem include the updated SMB 2.0 protocol,^[15] Offline Files, TCP window scaling and WAN optimization devices from various network vendors that cache and optimize SMB 1.0^[16] and 2.0.^[17]

Barry Feigenbaum originally designed SMB at IBM in early 1983 with the aim of turning DOS INT 21h local file access into a networked file system.^[3] Microsoft made considerable modifications to the most commonly used version and included SMB support in the LAN Manager operating system it had started developing for OS/2 with 3Com around 1990.^[18][19][20] Microsoft continued to add features to the protocol in Windows for Workgroups (c. 1992) and in later versions of Windows. LAN Manager authentication was implemented based on the original legacy SMB specification’s requirement to use IBM «LAN Manager» passwords, but implemented DES in a flawed manner that allowed passwords to be cracked.^[21] Later, Kerberos authentication was also added. The Windows domain logon protocols initially used 40-bit encryption outside of the United States, because of export restrictions on stronger 128-bit encryption^[22] (subsequently lifted in 1996 when President Bill Clinton signed Executive Order 13026^[23]).

SMB 1.0 (or SMB1) was originally designed to run on NetBIOS Frames (NetBIOS over IEEE 802.2). Since then, it has been adapted to NetBIOS over IPX/SPX (NBX), and NetBIOS over TCP/IP (NetBT). Also, since Windows 2000, SMB runs on TCP using TCP port 445, a feature known as «direct host SMB».^[24] There is still a thin layer (similar to the Session Message packet of NetBT’s Session Service) between SMB and TCP.^[24] Windows Server 2003, and legacy NAS devices use SMB1 natively.

SMB1 is an extremely chatty protocol, which is not such an issue on a local area network (LAN) with low latency. It becomes very slow on wide area networks (WAN) as the back and forth handshake of the protocol magnifies the inherent high latency of such a network. Later versions of the protocol reduced the high number of handshake exchanges. One approach to mitigating the inefficiencies in the protocol is to use WAN optimization products such as those provided by Riverbed, Silver Peak, or Cisco. A better approach is to upgrade to a later version of SMB. This includes upgrading both NAS devices as well as Windows Server 2003. The most effective method to identify SMB1 traffic is with a network analyzer tool, such as Wireshark. Microsoft also provides an auditing tool in Windows Server 2016 to track down devices that use SMB1.^[25]

Microsoft has marked SMB1 as deprecated in June 2013.^[26] Windows Server 2016 and Windows 10 version 1709 do not have SMB1 installed by default.^[27]

In 1996, when Sun Microsystems announced WebNFS,^[28] Microsoft launched an initiative to rename SMB to Common Internet File System (CIFS)^[3] and added more features, including support for symbolic links, hard links, larger file sizes, and an initial attempt at supporting direct connections over TCP port 445 without requiring NetBIOS as a transport (a largely experimental effort that required further refinement). Microsoft submitted some partial specifications as Internet Drafts to the IETF.^[6] These submissions have since expired.

Microsoft introduced a new version of the protocol (SMB 2.0 or SMB2) in 2006 with Windows Vista and Windows Server 2008.^[29] Although the protocol is proprietary, its specification has been published to allow other systems to interoperate with Microsoft operating systems that use the new protocol.^[30]

SMB2 reduces the ‘chattiness’ of the SMB 1.0 protocol by reducing the number of commands and subcommands from over a hundred to just nineteen.^[13] It has mechanisms for pipelining, that is, sending additional requests before the response to a previous request arrives, thereby improving performance over high-latency links. It adds the ability to compound multiple actions into a single request, which significantly reduces the number of round-trips the client needs to make to the server, improving performance as a result.^[13] SMB1 also has a compounding mechanism—known as AndX—to compound multiple actions, but Microsoft clients rarely use AndX.^{[citation needed]} It also introduces the notion of «durable file handles»: these allow a connection to an SMB server to survive brief network outages, as are typical in a wireless network, without having to incur the overhead of re-negotiating a new session.

SMB2 includes support for symbolic links. Other improvements include caching of file properties, improved message signing with HMAC SHA-256 hashing algorithm and better scalability by increasing the number of users, shares and open files per server among others.^[13] The SMB1 protocol uses 16-bit data sizes, which amongst other things, limits the maximum block size to 64K. SMB2 uses 32- or 64-bit wide storage fields, and 128 bits in the case of file-handles, thereby removing previous constraints on block sizes, which improves performance with large file transfers over fast networks.^[13]

Windows Vista/Server 2008 and later operating systems use SMB2 when communicating with other machines also capable of using SMB2. SMB1 continues in use for connections with older versions of Windows, as well various vendors’ NAS solutions. Samba 3.5 also includes experimental support for SMB2.^[31] Samba 3.6 fully supports SMB2, except the modification of user quotas using the Windows quota management tools.^[32]

When SMB2 was introduced it brought a number of benefits over SMB1 for third party implementers of SMB protocols. SMB1, originally designed by IBM, was reverse engineered, and later became part of a wide variety of non-Windows operating systems such as Xenix, OS/2 and VMS (Pathworks). X/Open standardized it partially; Microsoft had submitted Internet-Drafts describing SMB2 to the IETF, partly in response to formal IETF standardization of version 4 of the Network File System in December 2000 as IETF RFC 3010;^[33] however, those SMB-related Internet-Drafts expired without achieving any IETF standards-track approval or any other IETF endorsement. (See http://ubiqx.org/cifs/Intro.html for historical detail.) SMB2 is also a relatively clean break with the past. Microsoft’s SMB1 code has to work with a large variety of SMB clients and servers. SMB1 features many versions of information for commands (selecting what structure to return for a particular request) because features such as Unicode support were retro-fitted at a later date. SMB2 involves significantly reduced compatibility-testing for implementers of the protocol. SMB2 code has considerably less complexity since far less variability exists (for example, non-Unicode code paths become redundant as SMB2 requires Unicode support).

Apple migrated to SMB2 (from their own Apple Filing Protocol, now legacy) starting with OS X 10.9 «Mavericks».^[34] This transition was fraught with compatibility problems though.^[35][36] Non-default support for SMB2 appeared in fact in OS X 10.7, when Apple abandoned Samba in favor of its own SMB implementation called SMBX^[34] after Samba adopted GPLv3.^[37][38]

The Linux kernel’s CIFS client file system has SMB2 support since version 3.7.^[39]

SMB 2.1, introduced with Windows 7 and Server 2008 R2, introduced minor performance enhancements with a new opportunistic locking mechanism.^[40]

SMB 3.0 (previously named SMB 2.2)^[41] was introduced with Windows 8^[41] and Windows Server 2012.^[41] It brought several significant changes that are intended to add functionality and improve SMB2 performance,^[42] notably in virtualized data centers:

• the SMB Direct Protocol (SMB over remote direct memory access [RDMA])
• SMB Multichannel (multiple connections per SMB session),^[43][44]
• SMB Transparent Failover^[45][46]

It also introduces several security enhancements, such as end-to-end encryption and a new AES based signing algorithm.^[47][48]

SMB 3.0.2 (known as 3.02 at the time) was introduced with Windows 8.1 and Windows Server 2012 R2;^[49][50] in those and later releases, the earlier SMB version 1 can be optionally disabled to increase security.^[51][52]

SMB 3.1.1 was introduced with Windows 10 and Windows Server 2016.^[53] This version supports AES-128 GCM encryption in addition to AES-128 CCM encryption added in SMB3, and implements pre-authentication integrity check using SHA-512 hash. SMB 3.1.1 also makes secure negotiation mandatory when connecting to clients using SMB versions that support it.^[54]

The specifications for the SMB are proprietary and were initially closed, thereby forcing other vendors and projects to reverse-engineer the protocol to interoperate with it. The SMB 1.0 protocol was eventually published some time after it was reverse engineered, whereas the SMB 2.0 protocol was made available from Microsoft’s Open Specifications Developer Center from the outset.^[55]

In 1991, Andrew Tridgell started the development of Samba, a free-software re-implementation (using reverse engineering) of the SMB/CIFS networking protocol for Unix-like systems, initially to implement an SMB server to allow PC clients running the DEC Pathworks client to access files on SunOS machines.^[3][56] Because of the importance of the SMB protocol in interacting with the widespread Microsoft Windows platform, Samba became a popular free software implementation of a compatible SMB client and server to allow non-Windows operating systems, such as Unix-like operating systems, to interoperate with Windows.

As of version 3 (2003), Samba provides file and print services for Microsoft Windows clients and can integrate with a Windows NT 4.0 server domain, either as a Primary Domain Controller (PDC) or as a domain member. Samba4 installations can act as an Active Directory domain controller or member server, at Windows 2008 domain and forest functional levels.^[57]

Package managers in Linux distributions can search for the cifs-utils package. The package is from the Samba maintainers.

NSMB (Netsmb and SMBFS) is a family of in-kernel SMB client implementations in BSD operating systems. It was first contributed to FreeBSD 4.4 by Boris Popov, and is now found in a wide range of other BSD systems including NetBSD and macOS.^[58] The implementations have diverged significantly ever since.^[59]

The macOS version of NSMB is notable for its now-common scheme of representing symlinks. This «Minshall-French» format shows symlinks as textual files with a .symlink extension and a Xsym\n magic number, always 1067 bytes long. This format is also used for storing symlinks on native SMB servers or unsupported filesystems. Samba supports this format with an mfsymlink option.^[60] Docker on Windows also seems to use it.^{[citation needed]}

NQ is a family of portable SMB client and server implementations developed by Visuality Systems, an Israel-based company established in 1998 by Sam Widerman, formerly the CEO of Siemens Data Communications. The NQ family comprises an embedded SMB stack (written in C), a Pure Java SMB Client, and a storage SMB Server implementation. All solutions support the latest SMB 3.1.1 dialect. NQ for Linux, NQ for WinCE, iOS, Android, VxWorks and other real-time operating systems are all supported by the configurable NQ solution.

MoSMB is a user space SMB implementation for Linux. It supports SMB 2.x and SMB 3.x. Key features include Cloud-scale Active-Active Scale-out Clusters, SMB Direct (RDMA), SMB Multichannel, Transparent Failover and Continuous Availability. MoSMB also supports Amazon S3 object storage as storage backend in addition to POSIX file systems such as ext4, ZFS, Lustre, Ceph, etc.^[61]

Fusion File Share by Tuxera is a proprietary SMB server implementation developed by Tuxera that can be run either in kernel or user space.^[62] It supports SMB 3.1.1 and all previous versions, additionally advanced SMB features like continuous availability (persistent handles) scale-out, RDMA (SMB Direct), SMB multichannel, transparent compression, shadow copy.

Likewise developed a CIFS/SMB implementation (versions 1.0, 2.0, 2.1 and SMB 3.0) in 2009 that provided a multiprotocol, identity-aware platform for network access to files used in OEM storage products built on Linux/Unix based devices. The platform could be used for traditional NAS, Cloud Gateway, and Cloud Caching devices for providing secure access to files across a network. Likewise was purchased by EMC Isilon in 2012.

KSMBD is an open source in-kernel CIFS/SMB server implementation for the Linux kernel. Compared to user-space implementations, it provides better performance and makes it easier to implement some features such as SMB Direct. It supports SMB 3.1.1 and previous versions.

Over the years, there have been many security vulnerabilities in Microsoft’s implementation of the protocol or components on which it directly relies.^[63][64] Other vendors’ security vulnerabilities lie primarily in a lack of support for newer authentication protocols like NTLMv2 and Kerberos in favor of protocols like NTLMv1, LanMan, or plaintext passwords. Real-time attack tracking^[65] shows that SMB is one of the primary attack vectors for intrusion attempts,^[66] for example the 2014 Sony Pictures attack,^[67] and the WannaCry ransomware attack of 2017.^[68] In 2020, two SMB high-severity vulnerabilities were disclosed and dubbed as SMBGhost (CVE-2020-0796) and SMBleed (CVE-2020-1206), which when chained together can provide RCE (Remote Code Execution) privilege to the attacker.^[69]

• «[MS-CIFS]: Common Internet File System (CIFS) Protocol». Open Specifications. Microsoft. 30 October 2020.
  • Specifies the Common Internet File System (CIFS) Protocol, a cross-platform, transport-independent protocol that provides a mechanism for client systems to use file and print services made available by server systems over a network
• «[MS-SMB]: Server Message Block (SMB) Protocol». Open Specifications. Microsoft. 25 June 2021.
  • Specifies the Server Message Block (SMB) Protocol, which defines extensions to the existing Common Internet File System (CIFS) specification that have been implemented by Microsoft since the publication of the CIFS specification.
• «[MS-SMB2]: Server Message Block (SMB) Protocol Versions 2 and 3». Open Specifications. Microsoft. 14 December 2021.
  • Specifies the Server Message Block (SMB) Protocol Versions 2 and 3, which support the sharing of file and print resources between machines and extend the concepts from the Server Message Block Protocol.
• «[MS-SMBD]: SMB2 Remote Direct Memory Access (RDMA) Transport Protocol». Open Specifications. Microsoft. 25 June 2021.
  • Specifies the SMB2 Remote Direct Memory Access (RDMA) Transport Protocol, a wrapper for the existing SMB2 protocol that allows SMB2 packets to be delivered over RDMA-capable transports such as iWARP or Infiniband while utilizing the direct data placement (DDP) capabilities of these transports. Benefits include reduced CPU overhead, lower latency, and improved throughput.

• DFS section in «Windows Developer» documentation
• the NT LM 0.12 dialect of SMB. In Microsoft Word format