Microsoft recently acknowledged that its September 2025 security updates are disrupting SMBv1 file shares using NetBIOS over TCP/IP (NetBT). Systems with SMBv1 enabled on Windows 10, Windows 11, and Windows Server are experiencing failed connectivity for shares. Administrators report that the update has impacted both client and server sides.
Why This Matters
- SMBv1 is a deprecated protocol without modern security features. It has long been considered a liability due to its history of exploitation (e.g., ransomware).
- Disruption of file sharing can hamper business operations, especially in mixed or legacy environments that still rely on SMBv1.
- The break underlines how patching-even when addressing security issues-can unintentionally impact functionality if legacy components are still part of infrastructure.
Impacted Systems
- Windows 10 (earlier builds) and Windows 11 devices with SMBv1 over NetBT enabled.
- Windows Server instances where SMBv1 is still active.
- Legacy network storage devices and mixed-OS environments depending on SMBv1.
Recommended Actions
- Enable TCP port 445 traffic to allow SMB connections over TCP instead of NetBT as a workaround.
- Audit your network to find all systems still using SMBv1; plan to disable or phase out its use.
- Migrate shares to use more secure protocols like SMBv2 or SMBv3.
- After applying security updates, validate that file shares and network functionality are working as expected.
- Keep systems updated and monitor Microsoft’s fixes for this issue.
What This Incident Reveals
- Legacy protocols continue to be a weak point; even deprecated features can cause major issues if still in use.
- Security updates need to be tested in environments that include legacy systems to detect such disruptions early.
- Organizations should balance security with operational continuity by ensuring that infrastructure modernization is part of their cyber hygiene strategy.
About COE Security
COE Security helps organizations in financial services, healthcare, retail, manufacturing, and government to modernize their IT infrastructure, reduce risk, and maintain compliance. Our services include:
- AI-enhanced threat detection and monitoring
- Data governance aligned with GDPR, HIPAA, PCI DSS
- Secure model validation and adversarial defenses
- Customized training in cybersecurity best practices
- Penetration testing across Mobile, Web, AI, IoT, Network, and Cloud domains
- Secure Software Development Lifecycle consulting (SSDLC)
- Comprehensive Cybersecurity Services
We assist enterprises in auditing legacy dependencies, modernizing file sharing protocols, and ensuring resilience against both security threats and operational disruptions.
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