Microsoft has made a significant change in its approach to network security by dropping SMB1 Windows Defender Firewall rules in the latest Windows 11 build, commencing with the Canary Channel Insider Preview Build 25992. Until now, Windows 11 automatically added SMB1 Windows Defender Firewall rules when creating new SMB shares, establishing them within the “File and Printer Sharing” group for specific firewall profiles.
However, this alteration configures the updated “File and Printer Sharing (Restrictive)” group, excluding inbound NetBIOS ports 137-139, which are considered SMB1 artifacts. This change not only bolsters network security but also aligns SMB firewall rules more closely with the Windows Server “File Server” role behavior.
Administrators are granted the flexibility to configure the “File and Printer Sharing” group and make modifications to the new firewall group as needed. Moreover, future updates are planned to further refine the rule set by removing inbound ICMP, LLMNR, and Spooler Service ports while restricting them to the essential ports for SMB sharing.
These changes are part of Microsoft’s extensive effort to enhance Windows and Windows Server security, as reflected in recent updates. In addition, administrators can now enforce SMB client encryption for all outbound connections, ensuring secure connections by requiring destination servers to support SMB 3.x and encryption, thus mitigating eavesdropping and interception risks.
Furthermore, Windows 11 systems can be configured to automatically block the sending of NTLM data over SMB on remote outbound connections, thus thwarting pass-the-hash, NTLM relay, and password-cracking attacks. The initiative to strengthen security also encompasses requiring SMB signing by default for all connections to defend against NTLM relay attacks.
Microsoft is phasing out the decades-old SMB1 file-sharing protocol for Windows 11 Home Insiders, and additional measures to protect against brute-force attacks include the introduction of an SMB authentication rate limiter in September 2022, designed to mitigate the impact of unsuccessful inbound NTLM authentication attempts. These collective efforts aim to create a more secure Windows environment and reduce the vulnerabilities associated with various security threats.