SMBv1 shares broken by September Patch Tuesday update, Microsoft confirms

Microsoft has confirmed that the September Patch Tuesday updates are breaking connections to SMBv1 shares for some users.

The problem reportedly affects both Windows client and server platforms, including Windows 11 (24H2, 23H2, 22H2), Windows 10 (22H2, 21H2), Windows Server 2025, and Windows Server 2022.

According to a report by Bleeping Computer, the issue occurs when connecting to SMBv1 shares over the NetBIOS over TCP/IP (NetBT) protocol. Microsoft notes that failures may happen whether the update is installed on the client or the server side.

Until a full patch is released, Microsoft is recommending a workaround. Affected organizations can allow traffic on TCP port 445, which forces connections to use TCP instead of NetBT, restoring access to SMB shares.

As noted by the news outlet, the risks of using SMBv1 were highlighted in 2017, when leaked NSA-developed exploits like EternalBlue and EternalRomance were weaponized in major cyberattacks.

These exploits powered WannaCry and NotPetya, along with malware families such as TrickBot and Emotet, leading to widespread damage.

Microsoft says it is actively working on a permanent fix. For now, admins who still have SMBv1 enabled should apply the TCP workaround or, where possible, upgrade systems to SMBv2 or newer for long-term security.