In the ever-evolving landscape of cybersecurity, businesses must disable SMBv1 to stay ahead of vulnerabilities, especially in Windows environments. A recent report from Microsoft highlights a significant issue with the September 2025 security updates, which are disrupting access to legacy SMBv1 file shares. If your organization is still using this outdated protocol, it could spell trouble—not just for connectivity, but for your overall security posture. In this article, we’ll break down the problem, explore the inherent risks of SMBv1, and outline practical mitigation steps to protect your business.
The September 2025 Update Issue: What Happened?
Server Message Block (SMB) is a protocol used for sharing files, printers, and other resources across a network. SMBv1, the original version, dates back to the 1980s and was designed for simpler networking needs. However, it hasn’t kept pace with modern security demands. Microsoft has long encouraged users to disable SMBv1 and migrate to SMBv2 or SMBv3, which offer enhanced performance and protection.
The September 2025 Windows security updates (applicable to Windows 11 versions 24H2, 23H2, and 22H2; Windows 10 versions 22H2 and 21H2; and servers like Windows Server 2025 and 2022) are causing connection failures to SMBv1 shares. This affects scenarios where SMBv1 is used over the NetBIOS over TCP/IP (NetBT) protocol. If either the client or server has the update installed, users may suddenly be unable to access shared files and folders.
Microsoft has acknowledged the issue and is actively working on a permanent fix. In the meantime, they’ve provided a temporary workaround: opening TCP port 445 in your firewall or network configuration. This allows SMB connections to switch from NetBT to direct TCP, restoring access without fully resolving the underlying compatibility problem. However, this is a band-aid solution that doesn’t address the real concern—why is your business still dependent on such an antiquated protocol? It’s time to disable SMBv1 for long-term security.
The Risks of Sticking with SMBv1
SMBv1 isn’t just incompatible with modern updates; it’s a security nightmare. Deprecated since 2014 and no longer installed by default in Windows 10 (version 1709) and later, it lacks the robust features of its successors. Here are the key risks your business faces if you’re still using it and haven’t taken steps to disable SMBv1:
- Exploitation by Malware and Ransomware: SMBv1’s vulnerabilities, including those exposed in the 2017 Shadow Brokers leak of NSA tools like EternalBlue and EternalRomance, have been weaponized in devastating attacks. Notable examples include the WannaCry ransomware outbreak in 2017, which infected over 200,000 computers worldwide, and NotPetya, which caused billions in damages. Other malware families like TrickBot, Emotet, Olympic Destroyer, and Retefe have leveraged these flaws for credential theft, data destruction, and lateral movement within networks.
- Lack of Modern Security Controls: Unlike SMBv2 and SMBv3, SMBv1 doesn’t support pre-authentication integrity checks, which prevent tampering during connection setup. It also fails to block insecure guest authentication and offers no defense against security downgrade attacks (where attackers force a connection to fall back to weaker protocols) or man-in-the-middle (MitM) exploits. This leaves your file shares open to unauthorized access and remote code execution with administrative privileges. Businesses should prioritize efforts to disable SMBv1 to mitigate these threats.
- Compliance and Operational Disruptions: Regulatory frameworks like GDPR, HIPAA, and PCI-DSS emphasize minimizing outdated software. Relying on SMBv1 could expose your business to compliance violations and fines. Moreover, as seen with the September updates, future patches could render your legacy systems unusable, leading to downtime, lost productivity, and costly emergency migrations.
In short, using SMBv1 is like leaving your front door unlocked in a high-crime neighborhood—it’s an invitation for cybercriminals. Don’t delay—disable SMBv1 today.
Mitigation Steps: How to Disable SMBv1
The good news? Transitioning away from SMBv1 is straightforward and essential for bolstering your cybersecurity. Microsoft has been phasing it out since 2017, disabling it by default in many Windows editions. Follow these steps to assess, mitigate, and eliminate your reliance on it:
1. Audit Your Network for SMBv1 Usage:
Start by identifying where SMBv1 is active. On Windows machines, open PowerShell as an administrator and run:
Get-WindowsOptionalFeature -online | Where-Object {$_.FeatureName -like "*SMB1*"}This will show if SMBv1 is enabled. For a network-wide scan, use tools like PowerShell scripts or third-party scanners (e.g., from Microsoft or open-source options like Nmap) to detect SMBv1 traffic. Check legacy devices, such as old printers, scanners, or embedded systems, that might require it.
2. Apply the Temporary Workaround for the September Update:
If you must maintain SMBv1 access in the short term, configure your firewall to allow inbound and outbound traffic on TCP port 445. This bypasses the NetBT issue without enabling new risks. However, treat this as a stopgap—do not rely on it long-term.
3. Disable SMBv1 on Windows Systems:
Once you’ve confirmed no critical dependencies, disable it via PowerShell:
Disable-WindowsOptionalFeature -Online -FeatureName SMB1ProtocolRestart the machine afterward. For domain environments, use Group Policy: Navigate to Computer Configuration > Administrative Templates > Network > Lanman Workstation, and enable “Enable insecure guest logons” only if needed during transition (then disable it). On servers, repeat the process and test thoroughly.
4. Migrate to SMBv2 or SMBv3:
Upgrade compatible devices to support newer protocols. Most modern Windows versions have SMBv2/3 enabled by default. For legacy hardware:
- Replace or virtualize outdated systems.
- Use intermediaries like file servers running SMBv3 to bridge old and new environments.
- Test migrations in a staging environment to avoid disruptions.
5.Enhance Overall Security:
Keep all systems patched with the latest updates, including the September 2025 ones once the SMBv1 fix is released.
- Keep all systems patched with the latest updates, including the September 2025 ones once the SMBv1 fix is released.
- Implement network segmentation to isolate legacy shares.
- Enable advanced threat protection tools, such as Windows Defender or endpoint detection solutions, to monitor for SMB exploits.
- Conduct regular vulnerability scans and employee training on secure file-sharing practices.
By following these steps, you’ll not only resolve the current update headache but also fortify your defenses against future threats. Remember, the key action is to disable SMBv1 across your network.
Conclusion: Secure Your Future Today
The September 2025 Windows updates serve as a stark reminder: SMBv1 is a relic that’s more liability than asset. Businesses clinging to it risk data breaches, operational halts, and regulatory headaches. If your audit reveals SMBv1 in use, prioritize migration—it’s a small investment that yields massive security returns. For more tailored advice, consult your IT team or a cybersecurity expert. Stay vigilant and keep your network evolving with the times.
Click here to read more blog articles!