Guest user permits access to a database for any logins that are not mapped to a specific database user. The guest user cannot be dropped but it can be disabled by revoking the CONNECT permission. The recommendation is not valid for master, msdb, and tempdb system databases. If the Guest user is disabled in msdb system database, it may cause some issues.
The distribution database is also a system database and more information about the Guest User in the distribution database can be
found below. It is recommended to disable a guest user in every database as a best practice for securing the SQL Server.
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