In a stunning revelation, Microsoft has confirmed that its September 2025 Windows security updates are wreaking havoc for users relying on Server Message Block (SMB) v1 shares.

This widespread connection debacle affects a vast array of platforms, including various versions of Windows 11 (24H2, 23H2, 22H2) and Windows 10 (22H2, 21H2), as well as Windows Server 2025 and 2022.

According to an official service alert uncovered by BleepingComputer, the issue arises when users attempt to connect to SMBv1 shares using the NetBIOS over TCP/IP (NetBT) protocol.

Microsoft warns, "After installing the September 2025 Windows security update or later, connectivity issues with shared files and folders over the SMBv1 protocol using NetBT may occur." This problem can manifest if either the SMB client or server has the September update installed.

While Microsoft scrambles to find a permanent fix, the tech giant has rolled out a temporary workaround for affected customers. By enabling traffic on TCP port 445, users can pivot to TCP connections, restoring access to their shared resources.

It's crucial to note that SMBv1 has been on life support for years. Originally superseded by SMBv2 in 2007 and officially deprecated in 2014, this outdated protocol is no longer installed by default in Windows 10 since version 1709 and Windows Server 1709.

Back in April 2022, Microsoft began phasing out SMBv1 for Windows 11 Home Insiders, continuing a trend first announced in June 2017. In fact, internal builds of Windows Server 2016 and Windows 10 Enterprise set the stage for the eventual removal of this relic.

For years, Microsoft has urged network admins to ditch SMBv1, as it lacks crucial security features found in newer versions, such as pre-authentication integrity checks and protection against man-in-the-middle attacks. The urgency intensified following the 2017 exposure of NSA exploits that preyed on the protocol's vulnerabilities.

As users cope with these connectivity headaches, the spotlight is on Microsoft to resolve this glitch swiftly and restore functionality for those still clinging to the aging SMBv1.