Windows 11 Can't Access SMB/Samba Shares: SMB Signing Fix

Cause: since Windows 11 24H2 the SMB client requires signing by default. NAS devices and Samba servers without signing stop working.

Check the client:

Get-SmbClientConfiguration | Select-Object RequireSecuritySignature, EnableInsecureGuestLogons

Quick fix (elevated PowerShell):

Set-SmbClientConfiguration -RequireSecuritySignature $false -Force

By GPO: Computer Configuration > Windows Settings > Security Settings > Local Policies > Security Options > Microsoft network client: Digitally sign communications (always) = Disabled.

Better fix: enable signing on the server and keep the client secure. In Samba, smb.conf:

[global]
   server signing = mandatory

Guest shares: 24H2 also blocks guest access. Enable it only if you really need it: Set-SmbClientConfiguration -EnableInsecureGuestLogons $true -Force.