SMB in 2025: Known Vulnerabilities, Evolution, and Mitigation Strategies

The Server Message Block (SMB) protocol continues to be a critical infrastructure component in Windows environments, facilitating the sharing of files and network resources. In 2025, its ubiquity represents both a functional advantage and a critical attack surface, making understanding and mitigating its vulnerabilities a top priority for cybersecurity professionals. This report delves into the historical evolution of SMB, its pervasiveness in on-premises and cloud environments, and the current state of known vulnerabilities.

The analysis reveals that legacy versions of SMB, particularly SMBv1, remain a significant risk due to their inherent insecurity and their role in high-profile past attacks such as WannaCry and NotPetya. Emerging threats in 2025 include artificial intelligence (AI)-based attacks that increase the sophistication of ransomware and phishing campaigns, often exploiting SMB weaknesses as an initial entry vector. SMBs are particularly vulnerable, facing a disproportionate impact from ransomware attacks due to limited resources and often outdated defenses.

The report highlights the critical importance of hardening practices, with Windows Server 2025 introducing new advanced security features to strengthen SMB defenses. Migration to the cloud, while beneficial, shifts the attack surface and requires specific security configurations for services such as Azure Files and AWS FSx. Key recommendations for 2025 include mandatory disabling of SMBv1, implementing SMB encryption and signing, adopting multi-factor authentication (MFA) and Kerberos, segmenting the network, and keeping systems up to date. It is also imperative to adopt a Zero Trust architecture and invest in employee security awareness training to build a resilient defense posture against evolving threats.

1. Introduction: The Enduring Role of SMB in Windows Ecosystems

The Server Message Block (SMB) protocol stands as a cornerstone of network communication, facilitating essential functions such as file and printer sharing across diverse environments. Its pervasiveness, spanning over three decades, underscores its critical role in both enterprise networks and the broader Internet. In 2025, understanding the security posture of SMB is not simply a technical exercise, but a strategic imperative, given the growing sophistication of cyber threats. This report aims to provide an in-depth analysis of known SMB vulnerabilities in Windows environments, tracing the evolution of the protocol, assessing its current deployment across on-premises and cloud infrastructures, detailing prevalent attack vectors, examining its deep connection to ransomware, and outlining advanced mitigation strategies.

SMB is a fundamental network file-sharing protocol that allows computers to communicate with each other and access shared files, printers, and other network resources. It functions as a client-server protocol, where a client makes requests to a server, facilitating file and printer sharing between computers and enabling remote file access. A user can open, read, create, modify, and delete files on a remote server as if they were local. Originally designed by IBM in the 1980s to transform local DOS file access into a network file system, SMB enabled files on separate computers to be accessed as if they were on the user's local hard drive, using a common network protocol. Its widespread adoption continues in enterprise networks and across the Internet, making it a critical component of modern IT infrastructure.

The cyber threat landscape of 2025 is characterized by increasing sophistication and relentless attacks, particularly targeting small and medium-sized businesses (SMBs). This dynamic environment requires a proactive and evolving approach to SMB security, going beyond reactive measures. The pervasiveness and critical function of SMB make it an inherently attractive target. Its ubiquity creates a large attack surface; Even minor flaws or misconfigurations can have widespread impact. This highlights that securing SMB is not just about fixing specific vulnerabilities, but about addressing a critical, high-value attack surface that is difficult to isolate or eliminate entirely. Organizations cannot simply “remove” SMB; they must rigorously secure it. The fundamental nature of SMB means that its vulnerabilities have a cascading effect across the entire network infrastructure, making its security an ongoing, high-priority effort, not a one-time fix.

The objectives of this report are to provide a comprehensive, forward-looking analysis of SMB vulnerabilities in Windows environments for 2025. We will provide historical context for the evolution of SMB, analyze its current prevalence and adoption trends, including in cloud services, detail common and emerging attack vectors and their impact, highlight the critical link between SMB vulnerabilities and ransomware, and outline advanced mitigation strategies and best practices for securing SMB in 2025.

2. The Evolution of the Server Message Block (SMB) Protocol

The Server Message Block (SMB) protocol has undergone significant transformations since its inception, evolving from a basic file sharing mechanism to a sophisticated enterprise-grade protocol. Understanding this history is critical to understanding the current security landscape, as legacy versions continue to pose substantial risks.

2.1 From IBM's Origins to Microsoft's Modern Iterations

SMB was initially developed by IBM in the 1980s, with the goal of enabling network file systems on DOS. Its original purpose was to allow files on separate computers to be accessed as if they were local, using a common network protocol. The first version of SMB ran over NetBIOS, primarily using TCP ports 137, 138, and 139 for name services, datagram services, and session services, respectively. In 1990, Microsoft integrated SMB into its LAN Manager product, marking a significant step in its widespread adoption across Windows ecosystems.
During the mid-1990s, with Windows 95, Microsoft attempted to rename SMB to Common Internet File System (CIFS) and published draft standards to the IETF. CIFS is now widely considered a legacy dialect, referring specifically to SMB 1.0, which is known for its "chatty" nature, poor performance over wide area networks, and inherent flaws. The Samba project, started in 1991 by Andrew Tridgell, aimed to reverse engineer the SMB/CIFS protocol to enable interoperability between UNIX-like operating systems and Windows networks.
The protocol has seen several significant updates:

• SMB 1.0 (1980s): The original protocol designed by IBM, later integrated by Microsoft. It provided basic file sharing functionality but had limited security features and is now considered unsafe for use.
• SMB 2.0 (2006): Introduced with Windows Vista and Windows Server 2008, it was a major overhaul. It significantly reduced the "chatter" of the protocol by simplifying the commands (from hundreds to 19), improved performance for large file transfers, and added "durable file handles" for seamless reconnection after short network interruptions.
• SMB 2.1 (2009): Released with Windows 7 and Windows Server 2008 R2, this minor update included improvements such as leasing and caching.
• SMB 3.0 (2012): Launched with Windows 8 and Windows Server 2012, SMB 3.0 (also known as SMB 2.2) introduced substantial changes to the protocol. Key features included SMB Direct (SMB over Remote Direct Memory Access - RDMA) and SMB Multichannel (multiple connections per SMB session) to increase performance, especially in virtualized data centers. It also introduced significant security and management capabilities.
• SMB 3.0.2 (2013): A minor update included in Windows 8.1 and Windows Server 2012 R2.
• SMB 3.1.1 (2015): Introduced with Windows 10 and Windows Server 2016, this version added enhanced security measures. These included end-to-end encryption, pre-authentication integrity checks (to protect against man-in-the-middle and protocol downgrade attacks), and support for network fault tolerance. It also introduced the AES-256-GCM and AES-256-CCM cipher suites for SMB encryption.
  

The evolution of SMB ports is equally significant. Port 139 (TCP) was historically used for older SMB dialects that relied on NetBIOS for networking. Port 445 (TCP) was adopted by Microsoft from Windows 2000 onwards for newer SMB dialects (SMB2, SMB3, etc.) to run directly over TCP without NetBIOS, proving to be more efficient. Port 445 is also used by Microsoft Directory Services (Microsoft-DS). Overall, SMB has evolved from a basic file sharing mechanism to a robust, enterprise-grade protocol optimized for performance, security, and reliability.

2.2 SMB Version Compatibility Between Windows Operating Systems

When an SMB connection is established between a client and a server, they negotiate to use the highest version of SMB that both systems support. This mechanism, while ensuring compatibility, introduces a significant security challenge: backwards compatibility debt. While modern versions of SMB (such as SMB 3.x) offer robust security features such as encryption and signing, the need to support older versions, such as SMB 1.0, can expose the entire network to known and critical risks. SMB 1.0 is explicitly described as "inherently insecure" and has been at the center of high-profile attacks such as the WannaCry ransomware. Microsoft has deprecated it and recommends disabling it.
However, if a legacy device only requires or supports SMBv1 on the network, the connection will degrade to this less secure version unless SMBv1 is explicitly disabled on all endpoints. This means that securing a network depends not only on adopting the latest protocols, but also on actively managing and eliminating dependencies on legacy ones. Organizations must proactively audit their environments for SMBv1 dependencies and implement stringent policies to disable it, rather than assuming that modern operating system defaults are sufficient for the entire network. This tension between operational compatibility and security is an ongoing challenge that requires strategic attention. The following table summarizes SMB version compatibility with Windows operating systems:
Table 1: SMB Version Support for Windows Operating System

Modern Windows workstations (Windows 10 and 11) should be compatible with SMBv2 and SMBv3 and should not rely on SMBv1 for file sharing.

3. SMB Pervasiveness and Usage Landscape in 2025

The persistence of SMB in the IT landscape in 2025 is remarkable, evidenced by its widespread adoption in both on-premises and increasingly in cloud infrastructures. This pervasiveness, however, introduces new challenges and security considerations, as the attack surface evolves with migration to the cloud.

3.1 Widespread Adoption in Enterprise and Small and Medium Business (SMB) Networks

SMB continues to be widely used in enterprise networks and on the Internet. It is a fundamental protocol for sharing files, printers, and intercommunicating systems in local networks and on the Internet. Its relevance is particularly accentuated in small and medium businesses (SMBs), which represent a significant part of the enterprise landscape. In 2025, it is estimated that there will be over 34.8 million small businesses in the United States, representing 99.9% of all businesses. SMBs employ 45.9% of private sector workers, or 59 million people.
SMBs are investing significantly in technology, with an increasing emphasis on online operations. In 2024, 38% of SMBs added online/digital operations, leading to technology investments to support this digitization. This includes internet bandwidth upgrades (66% of respondents). While SMBs use fewer applications on average than large organizations, they show a higher density of apps per employee. The fastest growing app categories for SMBs include security tools (61% increase year-over-year in unique users) and compliance and security apps.
These data underscore that despite the emergence of new technologies and paradigms, SMB remains an essential network protocol for SMBs and large enterprises. Its continued relevance means that SMB vulnerabilities are not marginal issues, but core risks that can impact a broad user base and critical business functions.

3.2 SMB in Cloud Environments: Azure Files and AWS FSx

The shift to cloud computing is a dominant trend in 2025, with over 90% of organizations using the cloud and 60% running more than half of their workloads in the cloud. SMBs are leading this adoption, with over half of their technology budgets going to cloud services in 2025. It is expected that 63% of SMB workloads and 62% of SMB data will be hosted in the public cloud by next year. By 2025, it is expected that over 85% of SMBs will adopt “cloud-first” strategies.
In this context, SMB plays a crucial role in facilitating file sharing across hybrid and cloud environments. Services such as Microsoft’s Azure Files and AWS’s Amazon FSx for Windows File Server extend SMB capabilities to the cloud, allowing organizations to leverage the scalability and resiliency of the cloud while maintaining familiarity with the SMB protocol.
Migration to the cloud, while offering significant scalability, cost, and resiliency benefits, introduces a change in the attack surface for organizations. Traditional operating system vulnerabilities remain relevant, but they are joined by new cloud-specific threats, such as cloud misconfigurations, publicly exposed storage, and weakly configured access keys. This means that as organizations move to the cloud, their attack surface is not simply shrinking, but transforming, requiring a new set of security skills and tools.
SMB remains relevant even in a cloud-dominated landscape, especially in hybrid scenarios and for specific workloads that require compatibility with Windows file systems. For example, Azure Files manages hundreds of millions of file shares with billions of files, supporting large-scale production workloads, including business-critical application data, general and departmental shares, and hybrid data sets with seamless cloud tiering. Similarly, Amazon FSx for Windows File Server is used by companies such as 3M and Vital Energy to host SQL Server databases and seismic analysis data, benefiting from high availability, scalability, and improved performance.
Hybrid and multi-cloud architectures are becoming the norm, with 89% of companies using multi-cloud solutions and 80% adopting hybrid strategies. This added complexity requires organizations to implement consistent and robust SMB security policies across different platforms, managing integration between on-premises and multiple clouds. Securing SMB in these distributed environments becomes more complex, requiring careful management of network configurations, access controls, and encryption practices.

Table 2: SMB Cloud Services Adoption and Key Security Features

Security in cloud environments should prioritize the implementation of end-to-end encryption for data in transit and at rest, regular security audits, vulnerability assessments, detailed access logs, and robust authentication measures. Smart organizations add extra protection for cloud-connected SMB shares, such as strong data encryption and careful user access management.

4. The State of Known SMB Vulnerabilities in 2025

Despite continued improvements, the SMB protocol remains a frequent target for attackers due to its inherent weaknesses and pervasiveness. In 2025, awareness of SMB vulnerabilities is essential for network administrators, as SMB-related attacks have increased significantly over the past year.

4.1 The Persistent Threat of Legacy SMBv1

SMBv1, the original version of the protocol, is considered inherently insecure due to its outdated design, unencrypted connections, and weak authentication methods. Its deprecation by Microsoft and recommendation to disable it are direct consequences of its role in high-profile attacks.
The most notable example is the May 2017 WannaCry ransomware attack, which used EternalBlue, an exploit developed by the US National Security Agency (NSA) and leaked by The Shadow Brokers. WannaCry targeted computers running Microsoft Windows, encrypting data and demanding payment in Bitcoin. It propagated by scanning vulnerable systems and using the EternalBlue exploit to gain access and the DoublePulsar tool to install and run a copy of itself. Organizations that had not installed Microsoft's March 2017 security update were affected, particularly those running unsupported versions of Windows such as Windows XP and Windows Server 2003.
Another notable attack was NotPetya (June 2017), a variant of Petya malware that encrypted files and the master boot record (MBR), rendering infected Windows computers unusable. NotPetya exploited multiple propagation methods, including PsExec, WMI, and EternalBlue (the same SMBv1 exploit used by WannaCry) and EternalRomance, another SMBv1 exploit. These incidents demonstrated SMBv1's ability to act as a vector for "wormable" attacks, allowing malware to spread rapidly across networks.

4.2 Common SMB Attack Vectors and Their Impact

SMB implementations contain numerous security weaknesses that expose organizations to potential threats. Microsoft research indicates that authentication vulnerabilities cause a large number of SMB-related security incidents.
Authentication Weaknesses: Poor password practices and insufficient credential checks create significant security gaps. Many SMB servers still accept basic authentication methods, making them targets for brute force attacks and credential theft when stronger security protocols are not enforced.
Protocol Implementation Flaws:
Buffer Overflow: This is a critical vulnerability that can lead to memory corruption and arbitrary code execution. Attackers can exploit buffer overflow weaknesses to execute malicious code. For example, Samba (an open source SMB server) was vulnerable to a remote stack-based buffer overflow in the reply_netbios_packet() function.
Protocol Downgrade: This high-impact attack forces a connection to switch from a highly secure protocol to an older, less secure version. Attackers can intercept the protocol negotiation phase and modify it to force the client and server to agree to use an older, more vulnerable SMB version. This can allow attackers to exploit known vulnerabilities in the degraded protocol to decrypt, modify, or inject malicious data.
Session Hijacking: This medium-impact attack involves intercepting and taking over authenticated sessions. Attackers with access to the same network as the client or server can interrupt, terminate, or steal an ongoing session. They can intercept and modify unsigned SMB packets to cause the server to perform questionable actions, or impersonate the server or client after legitimate authentication to gain unauthorized access to data.
Specific Attack Techniques:
SMB Relay Attacks: Attackers exploit the inherent trust of the SMB protocol by intercepting and forwarding authentication attempts to gain unauthorized access to network resources. This attack often exploits the NTLM authentication mechanism and can be achieved by positioning themselves as a "man-in-the-middle" (e.g., via ARP spoofing or DNS poisoning) to redirect SMB traffic through the attacker's machine.
Pass-the-Hash Attacks: This common technique exploits weaknesses in SMB to steal authentication credentials and potentially control the domain. Instead of cracking the password, attackers use a stolen password hash to authenticate themselves as a user without knowing the actual password, allowing lateral movement across the network. Tools such as Mimikatz are commonly used to extract hashes and conduct these attacks.

4.3 The Critical Nexus: SMB Vulnerabilities and Active Directory Integration

SMB vulnerabilities become particularly dangerous when they connect to Active Directory (AD) services, creating potential entry points throughout the network infrastructure. Active Directory operations depend on SMB for critical functions such as user authentication and resource sharing. Research indicates that the majority of Active Directory attacks arise from compromised SMB connections. Communication between client systems and AD domain controllers occurs over SMB channels when accessing network resources, making this connection a vital security focal point.
Attacks often target SMB vulnerabilities to infiltrate Active Directory environments. Malicious actors frequently use SMB relay attacks, intercepting SMB authentication requests for privilege escalation. Pass-the-hash attacks, as mentioned, exploit SMB weaknesses, leading to the theft of authentication credentials and potential takeover of the domain.

4.4 Notable SMB-Related Vulnerabilities and Exploits (2024-2025)

2024 and 2025 have seen and will continue to see a steady stream of vulnerabilities that, while not all directly in the SMB protocol, can significantly impact Windows environments that use SMB. Remote code execution (RCE) and escalation of privilege (EoP) vulnerabilities are the most common.
Notable CVEs (2024-2025):

• CVE-2025-29956: A specific SMB vulnerability that allows an authorized attacker to disclose information over a network via a buffer over-read in Windows SMB. It has a CVSS score of 5.4.
• CVE-2022-32230: A Denial of Service (DoS) vulnerability in the Windows SMB protocol (SMBv3) that can cause a Windows kernel crash (Blue Screen of Death - BSOD) by sending a malformed SMBv3 FileNormalizedNameInformation request over a named pipe. It has a CVSS score of 7.5.
• CVE-2020-0796: A remote code execution (RCE) vulnerability in SMBv3.1.1, also known as "Wormable" or "SMBGhost". Although it was discovered in 2020, its "wormable" nature and critical impact make it a benchmark for newer SMB vulnerabilities.
• CVE-2025-24054: A Windows NTLM hash disclosure vulnerability that was exploited in attack campaigns in March 2025. It allows attackers to capture the NTLMv2 response and attempt offline brute force or relay attacks. While not directly an SMB vulnerability, it does exploit the NTLM authentication often used with SMB.
• Zero-Day Vulnerabilities: As of May 2025, Microsoft has fixed 72 vulnerabilities, including five actively exploited zero-day vulnerabilities. While not all are directly related to SMB, some such as vulnerabilities in the Windows Common Log File System driver (CVE-2025-32701, CVE-2025-32706) and the Windows Ancillary Function Driver for WinSock driver (CVE-2025-32709) have been exploited for privilege escalation. These privilege escalation vulnerabilities can be used by attackers to gain more control over compromised systems, which can then facilitate access and exploitation of SMB shares.
• CVE-2025-37899: A zero-day vulnerability in the Linux kernel (ksmbd component, which handles the SMB3 protocol) discovered using a large language model (OpenAI o3). It is a use-after-free vulnerability in the handling of the SMB2 LOGOFF command. While not specific to Windows, it highlights the potential of AI in discovering complex vulnerabilities in network protocols like SMB and the “double-edged” nature of AI in cybersecurity (both for defense and offense).
  

Table 3: Key SMB-Related CVEs (2024-2025) with CVSS Scores and Impact

Windows Common Log File System (CLFS) vulnerabilities (e.g. CVE-2025-32701, CVE-2025-32706) and DWM Core Library (CVE-2025-30400), while not directly SMB, were actively exploited as zero-days in 2025, highlighting a general trend of EoP and RCE attacks in Windows environments. These types of vulnerabilities can be chained with SMB exploits to gain deeper control over systems.

5. Ransomware and SMB: The Escalating Threat in 2025

Ransomware continues to be one of the most profitable and destructive cyber threats, and in 2025, its impact on small and medium-sized businesses (SMBs) is particularly alarming.

5.1 The Disproportionate Impact on Small and Medium-Sized Businesses

Ransomware remains a financial nightmare for businesses of all sizes. Ransomware incidents are set to increase by approximately 25% in 2024, with data exfiltration (stealing sensitive data before encryption) nearly doubling in frequency. What’s even more concerning is that 82% of ransomware attacks hit businesses with fewer than 1,000 employees, making SMBs prime targets. 76% of SMBs have experienced a ransomware attack in the past year, exceeding the rate of attacks reported by large enterprises.
SMBs are often perceived as “easy fruit” due to their smaller size and often weaker security measures. Many small business owners hold onto the dangerous belief that “it won’t happen to us,” a complacency that is dangerous: 1 in 3 SMBs have experienced a cyberattack in the past year, and 32% say that even a single day of downtime (or about $10,000 in losses) could force them to close their doors. 75% of small businesses would go bankrupt if they suffered a ransomware attack. The average loss for SMBs due to security incidents in 2024 rose to $1.6 million, up from $1.4 million in 2023, highlighting that attacks are becoming more sophisticated and costly.
The ransomware ecosystem is becoming more sophisticated, with approximately 80 active ransomware groups globally and 16 new ones emerging since January 2025. This includes the growth of Ransomware-as-a-Service (RaaS), which has made it easier for less technical attackers to access and use sophisticated tools. Ransomware kits now include pre-built malware payloads, clear step-by-step instructions, and tools for lateral movement, privilege escalation, and encryption.

5.2 Initial Entry and Exploitation via SMB Vulnerabilities

SMB vulnerabilities serve as primary entry points for ransomware. The Verizon Data Breach Investigations Report (DBIR) 2025 highlights that vulnerability exploitation has grown as an initial entry vector for breaches, reaching 20%. Specifically, within the “System Intrusion” model, which is largely driven by ransomware (present in 75% of breaches in this model), vulnerability exploitation is the most common vector, surpassing credential abuse. This is especially relevant for ransomware, as ransomware operators have exploited vulnerabilities in file server software (in 2023) and edge devices (in 2024).

While DBIR 2025 does not explicitly specify “SMB vulnerabilities” as an initial entry vector, the high prevalence of ransomware in SMBs (88% of ransomware-related breaches in SMBs compared to 39% in large organizations) and the historical connection between SMBv1 and mass ransomware attacks such as WannaCry and NotPetya strongly imply that SMB vulnerabilities are a significant entry point. Attackers are exploiting SMB misconfigurations, outdated versions, and authentication weaknesses to gain an initial foothold in the network.

The emergence of artificial intelligence (AI) has intensified these attacks, allowing cybercriminals to reach more potential victims at scale, create more convincing impersonations, craft well-written messages without grammatical errors, and build detailed profiles of targets using aggregated data. AI-based phishing scams are booming and will be a major threat to SMBs in 2025 and beyond, with a 703% increase in credential-based phishing attacks identified in 2024.

5.3 Emerging Ransomware Tactics and Groups

The ransomware ecosystem continues to evolve rapidly. In March 2025, the RansomHub ransomware group emerged as a significant threat, leading with a victim count of 84. The manufacturing sector was the top target of ransomware attacks, with 91 incidents globally in March 2025. New groups such as Arkana, CrazyHunter, NightSpire, RALord, and VanHelsing have emerged in the ransomware landscape.

Tactics are evolving:
Triple Extortion Attacks: These attacks are on the rise, where attackers encrypt corporate data, exfiltrate it, and then threaten third parties (vendors, customers, and partners) connected to the victim. Triple extortion jumped to 14% of ransomware cases in the first half of 2023 and continues to rise.
Exploitation of IoT and Edge Devices: Some ransomware groups, such as Akira, may increasingly exploit IoT and edge devices to evade detection. Future attacks may target other Linux-based systems, such as security cameras, NAS devices, or industrial control systems, to gain persistence and perform encryption.
Dependence on Custom Malware: Future ransomware operations will likely increase their reliance on custom malware, such as Betruger, to improve stealth, persistence, and automation. Ransomware groups may reduce their reliance on public tools by developing all-in-one backdoors for pre-encryption tasks.
Ransomware and Supply Chain Attacks Convergence: 91% of organizations are concerned about ransomware attacks targeting their software supply chain, third-party partners, and connected partners. SMBs are particularly vulnerable to these supply chain threats, as they often rely on a small network of managed service providers and third-party platforms.
These developments underscore the need for organizations to adopt multi-layered defense strategies and stay up-to-date on the latest attacker tactics.

6. Advanced Mitigation Strategies and Best Practices for 2025

To address the evolving landscape of SMB vulnerabilities and ransomware threats in 2025, organizations must adopt a comprehensive and proactive security approach. This goes beyond simple patching and includes hardening measures, adopting new security features, and integrating advanced defense strategies.

6.1 Key Security Measures for SMB Protection

The following practices are essential to strengthen your SMB security posture:

Mandatory SMBv1 Disablement: SMBv1 is an outdated version of the protocol that is known for its security flaws and must be disabled on all devices. Microsoft has deprecated SMBv1 and recommends disabling it due to its vulnerability to attacks such as WannaCry. Disabling can be done via PowerShell (Disable-WindowsOptionalFeature -Online -FeatureName "SMB1Protocol") and requires a server reboot.
Enable SMB Encryption and Signing: SMB encryption, available starting with SMB 3.0, protects sensitive data in transit, ensuring end-to-end privacy and integrity between the file server and the client, regardless of the networks traversed. SMB signing helps prevent man-in-the-middle attacks that modify SMB packets in transit, preventing impersonation of client and server computers. Although signing can impact performance, it should be enabled for sensitive environments.
Implement Strong Authentication Mechanisms:
Multi-Factor Authentication (MFA): MFA adds an additional layer of security by requiring users to provide multiple forms of authentication to access resources. SMBs that do not use MFA (14% in 2025) are most vulnerable. Adoption of FIDO2, which uses biometric factors or hardware keys, is considered the “gold standard” for MFA.
Kerberos: A modern protocol with stronger security measures than NTLMv2, recommended for secure environments. Enabling Kerberos and disabling NTLMv2 is critical.
Principle of Least Privilege (PoLP): Assign permissions based on roles and regularly review and update permissions, avoiding the use of "Everyone" or "Authenticated Users".
Network Segmentation and Strict Firewall Configurations: Use Windows Firewall or a dedicated network firewall to restrict access to SMB ports (TCP 445 and 139). Configuring the firewall to limit SMB traffic to trusted IP addresses or internal networks can mitigate exposure to potential attackers. Isolate essential Active Directory resources on the network. Adherence to Strict Patch Management and Regular System Updates: Keeping your Windows Server environment up to date is critical to security. Enable automatic updates or schedule regular maintenance windows to apply security patches. 57% of data breaches could have been prevented by installing an available patch.

6.2 Windows Server 2025: New Hardening Features

Windows Server 2025 introduces several new SMB security features and hardening options to improve the protection of SMB traffic. These innovations are designed to address modern threats and provide administrators with more granular control:

SMB NTLM Disable: This feature is designed to block NTLM authentication for SMB connections, thereby improving security. It can be configured via Group Policy and PowerShell.
SMB Firewall Rule Hardening: This security feature aims to improve the protection of SMB traffic through several key aspects: stronger default security settings, mitigation of unauthorized access by limiting SMB port exposure, and integration with other security features such as SMB signing and NTLM deprecation to provide a comprehensive security posture.
SMB Authentication Rate Limiter: This feature is designed to counter brute force authentication attacks. The SMB Server service implements a delay between each failed authentication attempt based on NTLM or PKU2U.
SMB Dialect Control: This feature allows administrators to manage SMB2 and SMB3 dialects in Windows Server. Administrators can specify the SMB protocols used, blocking older, less secure versions from connecting to the server. This can be configured via Group Policy or PowerShell.
SMB Alternative Ports: The SMB client can now connect to alternative TCP, QUIC, and RDMA ports, other than their IANA/IETF defaults of 445, 5445, and 443. This can be configured via Group Policy or PowerShell.
Post-Quantum Resilient Kerberos: This enhanced security feature protects Kerberos authentication from potential threats posed by quantum computing. It incorporates cryptographic algorithms that are resistant to quantum attacks, ensuring that Kerberos authentication remains secure even as quantum computing advances.
Remote Mailslots Deprecated: Remote Mailslots are now deprecated and disabled by default for SMB and for using the DC locator protocol with Active Directory.

These features in Windows Server 2025 provide critical tools for administrators to improve SMB security, but require careful planning and implementation.

6.3 Securing SMB in Cloud Environments

With the increasing adoption of cloud, securing SMB in environments like Azure Files and AWS FSx has become a priority.
Azure Files:
Encryption in Transit: By default, all Azure file shares have encryption in transit enabled, allowing only SMB mounts using SMB 3.x with encryption. Azure Files supports AES-256-GCM with SMB 3.1.1 and AES-128-GCM with SMB 3.0.
Private Endpoints: Using private endpoints is strongly preferred over public exposure for Azure file shares. Private endpoints allow access to Azure file shares from your on-premises network without exposure to the public internet.
Azure AD Authentication and NTFS Permissions: Use Azure Active Directory authentication and NTFS permissions for granular control.
Storage Account and NSG Firewall: Use storage account firewall to restrict access by IP or VNet and Network Security Groups (NSG) to restrict traffic (port 445 for SMB).
Monitoring: Enable logging and monitoring with Azure Monitor and Azure Security Center to identify suspicious activity.
AWS FSx for Windows File Server:
Encryption at Rest and in Transit: All Amazon FSx file systems are encrypted at rest with keys managed by AWS Key Management Service (AWS KMS). Data is automatically encrypted before being written and decrypted when being read. Encryption in transit is supported for data between client and server.
Active Directory Integration: FSx for Windows File Server integrates with Active Directory for authentication and access control. It is critical to ensure that domain controllers are reachable and that service account credentials are valid.
Access Controls: Implement Windows ACLs and use Amazon VPC to control access to the file system.
Monitoring: Create a monitoring plan using file system metrics in Amazon CloudWatch to monitor storage usage and performance.

6.4 Proactive Defense and Strategic Cybersecurity Trends

In addition to technical configurations, a proactive and strategic approach to cybersecurity is critical to resilience in 2025.
Adopting Zero Trust Architecture and the Principle of Least Privilege: The guiding principle of Zero Trust is “never trust, always verify.” Every user, device, and application, regardless of physical location, must be authenticated and authorized before access is granted. This is a key element of the Principle of Least Privilege, which reduces the attack surface and limits the impact of potential breaches. SMBs must implement stringent access controls and monitor internal activities.
Leveraging AI in Cybersecurity Defense for Unified Detection and Response: AI is set to be the primary driver of change for SMB cybersecurity in 2025, particularly through its ability to power unified detection and response platforms. These AI-integrated platforms simplify and centralize cybersecurity operations, making security management significantly easier for SMBs and the managed service providers (MSPs) that serve them. AI can analyze large amounts of data quickly and accurately to identify anomalies, predict potential threats, and automate responses.
However, only 11% of SMBs have adopted AI-based security tools , leaving the vast majority unprepared for AI-enhanced attacks. This gap between awareness and action is a significant concern.
Importance of Continuous Employee Security Awareness Training and Phishing Simulations: Employees are the first line of defense against some of the most common cyber risks, such as social engineering. Security awareness training can reduce cyber risk by 60% within a year. Regular phishing simulations test employee vigilance and prepare them to recognize and report attack attempts.
The Strategic Role of Cyber ​​Insurance and Managed Security Service Providers (MSSPs): Cyber ​​insurance adoption is a key trend in 2025. Modern policies offer proactive risk management services, supporting SMBs with incident response planning, vulnerability assessments, and employee training. However, SMBs should not rely on insurance alone, but view it as part of a balanced approach.
Managed service providers (MSPs/MSSPs) can offer SMBs access to advanced tools such as unified detection and response platforms, threat intelligence feeds, and 24/7 monitoring, as well as bring expertise in regulatory compliance. Nearly 70% of SMBs rely on MSPs or external consultants to manage their cybersecurity strategies.

7. Conclusion and Future Outlook

The SMB protocol, despite its evolution and significant security improvements in its latest versions, remains a hot spot for vulnerabilities in Windows environments in 2025. Its ubiquity, both in on-premises and cloud networks, makes it a persistent and high-value target for attackers. The continued presence of SMBv1, although deprecated, represents a significant security debt that organizations must proactively address.
The threat landscape is rapidly evolving, with ransomware disproportionately targeting SMBs and artificial intelligence amplifying the sophistication of attacks. SMB vulnerabilities are often exploited as initial access vectors, allowing attackers to gain a foothold and compromise critical systems, including Active Directory environments.
To mitigate these risks, organizations must adopt a layered security approach. This includes rigorously implementing key best practices, such as disabling SMBv1, enabling SMB encryption and signing, and strong authentication enforcement (MFA, Kerberos). Adopting Windows Server 2025 provides advanced hardening capabilities that, if configured correctly, can significantly improve your security posture. SMB security in cloud environments requires specific attention to configuring services such as Azure Files and AWS FSx, ensuring private endpoints, end-to-end encryption, and granular access controls.
Looking ahead, cyber resilience will increasingly depend on adopting Zero Trust architectures, integrating AI into defenses for unified detection and response, and continuing to invest in employee security awareness. SMBs, in particular, need to overcome resource and skill limitations by leveraging strategic partnerships with MSPs and considering cyber insurance as part of a holistic risk management strategy. Continuous vigilance, adaptation, and a proactive security culture will be key to safeguarding digital assets in 2025 and beyond.