Event ID 1906: Session key for connection is weaker than required
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Windows 10.0.26200.0, 2026-10-28; the notes are ours, based on Microsoft's
security auditing reference.
Session key for connection is weaker than required.
Event 1906
SMBServer
SMBServer/Operational log
Error
Message and fields (as Event Viewer shows them)
Session key for connection is weaker than required. Connection will be closed as a result.
Client: …
User: …
Session key length: …
Required Session key length: …
Guidance:
To establish a connection with a shorter session key, set the following registry DWORD value name with the value as decimal bits:
[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\LanmanServer\Parameters]
"MinimumSessionKeyLength"
Important: If you have configured the 'Network security: Configure encryption types allowed for Kerberos' security policy to prevent use of 256-bit keys but also set the MinimumSessionKeyLength greater than 128 bits, the computer will not be able to make SMB connections. Setting MinimumSessionKeyLength higher than 128 bits will also prevent SMB connections using NTLM.