Microsoft just broke SMBv1 connections with their September 2025 security updates, and sysadmins are scrambling to fix shared folders and printers that went dark overnight. The issue affects SMBv1 shares over NetBIOS over TCP/IP (NetBT) connections.
Every Windows Version Is Fucked
Microsoft's service alert confirms this hits all current Windows versions - 10, 11, and Server editions. If you're running SMBv1 for file sharing, your shared folders and printers just went dark.
The problem hits when either the SMB client or server has the September patch. So even if half your network is patched and half isn't, everything breaks anyway. It's like Microsoft designed this to cause maximum pain.
Why SMBv1 Still Exists in 2025
Here's the thing about SMBv1: Microsoft has been trying to kill it since 2017. The protocol was superseded by SMBv2 in 2007 and deprecated in 2014. It's been disabled by default in newer Windows versions since 2017, yet somehow millions of organizations still rely on it.
The problem is legacy hardware that refuses to die. I've got clients with network printers from 2010 that still work perfectly - except they only speak SMBv1. Industrial control systems running Windows XP embedded, medical devices that cost $50K to replace, and random network-attached storage boxes that were "temporary" solutions in 2015 and somehow became permanent infrastructure.
Microsoft's been warning about SMBv1's security vulnerabilities since the WannaCry ransomware attack in 2017, which exploited weaknesses in the protocol. The NSA's leaked EternalBlue exploit specifically targeted SMBv1 flaws, leading to billions in damage when weaponized by cybercriminals.
The Temporary Workaround
Microsoft's recommended workaround involves opening TCP port 445 to force direct TCP connections instead of NetBT. This approach restores connectivity in many cases but doesn't address the underlying SMBv1 security concerns.
IT admins are getting mixed results with the workaround. Some factory couldn't print shipping labels for half a day while IT figured out the port settings. The fix works sometimes, but you're still running a 30-year-old protocol that's basically held together with duct tape and prayers.
This Breaks More Than Just File Sharing
Insurance companies now exclude breaches involving legacy protocols like SMBv1. Running it violates NIST cybersecurity frameworks and fails most security audits.
Manufacturing companies are shutting down production lines because their industrial control systems can't talk to the file server. Hospitals have X-ray machines that can't save images because they're stuck on legacy medical devices from the Obama administration. Law firms can't access client files because someone bought a document management system in 2012 and never bothered upgrading it.
Microsoft's been trying to kill SMBv1 since 2017, and every Patch Tuesday brings new ways to break legacy shit. This isn't a bug - it's Microsoft's way of saying "upgrade your crap or suffer."
Migration Pressure Increases
Organizations will likely face continued SMBv1 reliability issues until they migrate to SMBv2/SMBv3. Microsoft's ongoing deprecation efforts suggest future Windows versions may remove SMBv1 support entirely.
Audit your SMBv1 dependencies first. Network printers usually support SMBv2/SMBv3 with firmware updates. Legacy applications might work with file server modernization tools or Windows compatibility modes.
The alternative is continued exposure to dozens of active SMBv1 exploits that ransomware groups actively target. Security researchers note that organizations running SMBv1 in 2025 face significantly elevated cyberattack risks.
Microsoft has indicated they're developing a permanent fix, though no timeline has been provided. Industry analysts expect SMBv1 removal from Windows to accelerate, making migration planning critical for organizations still dependent on the legacy protocol.