Microsoft has acknowledged a significant issue with its September 2025 Windows security updates that prevents users from connecting to older file-sharing systems. The problem affects a wide range of Windows versions and highlights ongoing security concerns with legacy networking protocols.

## What’s Affected

The connectivity issue impacts both desktop and server versions of Windows, including:
– **Client systems**: Windows 11 (versions 24H2, 23H2, 22H2) and Windows 10 (versions 22H2, 21H2)
– **Server systems**: Windows Server 2025 and Windows Server 2022

The problem specifically affects connections to SMBv1 (Server Message Block version 1) file shares that use NetBIOS over TCP/IP networking. Users may find themselves unable to access shared files and folders after installing the security update.

## Temporary Fix Available

While Microsoft works on a permanent solution, the company has provided a workaround for affected users. The fix involves allowing network traffic on TCP port 445, which forces Windows to switch from NetBIOS to direct TCP connections for SMB file sharing.

## Why SMBv1 Remains a Security Risk

SMBv1 is an outdated protocol that Microsoft has been actively discouraging for years. Originally developed in the 1990s, it was replaced by more secure versions in 2007 and officially deprecated in 2014. Since Windows 10 version 1709, SMBv1 is no longer installed by default.

The protocol lacks critical security features found in newer versions, including:
– Protection against man-in-the-middle attacks
– Secure authentication mechanisms
– Defense against security downgrade attacks

## Historical Security Concerns

SMBv1’s vulnerabilities became widely known after the 2017 leak of NSA hacking tools that exploited weaknesses in the protocol. These exploits, including EternalBlue and EternalRomance, were later weaponized by major malware campaigns such as WannaCry, NotPetya, and TrickBot, causing billions in damages worldwide.

## Moving Forward

This latest issue serves as another reminder for organizations to migrate away from SMBv1 to more secure file-sharing protocols. While the temporary workaround addresses immediate connectivity problems, the long-term solution involves upgrading to SMBv2 or later versions that provide robust security protections against modern cyber threats.

Microsoft continues to work on resolving the compatibility issue while maintaining its stance that organizations should eliminate SMBv1 from their networks entirely.