Error 18456 occurs when a login attempt to SQL Server fails. This error is triggered by authentication issues such as incorrect usernames or passwords, disabled accounts, or mismatches between the authentication mode and the login credentials. SQL Server does not reveal the exact reason for the failure in the error message returned to the client to avoid security risks. Instead, a corresponding error state code provides more specific detail in the SQL Server error logs.
Each state code gives insight into why the login failed:
Admins should review the SQL Server logs to find the specific state number and use that to diagnose the issue further.
Q: Why don’t I see the reason for the login failure in the client error?
A: SQL Server deliberately hides detailed reasons for login failures to prevent attackers from gathering information.
Q: Where can I find the exact reason for error 18456?
A: Check the SQL Server error logs. The state code (e.g. 8, 11, 18) gives more specific context.
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