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Event ID 31017: Rejected an insecure guest logon

Windows Event ID Lookup: What Windows event IDs mean: 4625, 4624, 4740, 6008, 41, 7045, 1102 and 3,000 more, with Windows' own message text, the fields and what to check.

Look up a Windows event ID from Event Viewer, a SIEM alert or a log export: what it means, the fields it records, and what to check. Many IDs are used by more than one source (event 41 is both a Kernel-Power crash and a boot error), so every definition is shown, the one people usually mean first. The message text is Windows' own, read from the event providers of Windows 10.0.26200.0, 2026-10-28; the notes are ours, based on Microsoft's security auditing reference.

Try: 4625, 4624, 4740, 6008, 41, 1074, 7045, 1102, 4104, 1149

Rejected an insecure guest logon.

Event 31017
SMBClient
SMBClient/Connectivity log
Error
Message and fields (as Event Viewer shows them) 
Rejected an insecure guest logon.

User name: …
Server name: …

Guidance:
This event indicates that the server attempted to log the user on as an unauthenticated guest and was denied by the client. Guest logons do not support standard security features such as signing and encryption. As a result, guest logons are vulnerable to man-in-the-middle attacks that can expose sensitive data on the network. Windows disables insecure guest logons by default. Microsoft does not recommend enabling insecure guest logons.