What’s the issue?
Every SQL Server database has an owner SID stored in sys.databases, which links the database to a server-level principal in sys.server_principals. When the SID points to a login that exists on the instance, the owner can be resolved to a name and used by SQL Server for ownership-related operations.
When the owner SID does not match any existing login on the instance, the owner becomes effectively unknown. Queries that try to resolve the owner name return NULL or display the raw SID, and the database is considered to have no valid owner from the server’s perspective.
This finding identifies databases whose owner cannot be resolved to a current login. The condition most often appears after a database is restored from another instance where the original owner login does not exist on the destination, or after a login has been dropped without first reassigning the databases it owned.
Why is this a problem?
A database with an unresolvable owner has no functional trust anchor for ownership-related operations. Cross-database ownership chaining, certain permission resolutions, and operations that need to evaluate the owner’s identity can produce errors or NULL results, which can break stored procedures, jobs, and integrations that depend on consistent owner resolution.
The condition also produces audit findings, since reviewers cannot determine who is responsible for the database. The owner column appears blank or shows an unrecognizable SID, which makes it impossible to evaluate whether the ownership is appropriate or whether it represents a privilege escalation risk. This is particularly important because the issues described in the preferred owner finding (members of db_owner creating objects that execute as the owner) still apply even when the owner cannot be resolved by name.
Some SQL Server features behave unpredictably with unresolvable owners. Backup and restore operations may produce warnings, replication and Always On configurations can encounter errors during certain operations, and database mail or other features that resolve principals can fail in ways that are hard to diagnose without checking ownership first.
The condition often persists because it is invisible during normal use. The database functions for read and write operations, applications connect successfully, and routine maintenance runs without obvious problems. The unknown owner only surfaces during specific operations or during security reviews, by which time the original context for who should own the database may have been lost.
What should you do about this?
Reassign ownership to a valid login using ALTER AUTHORIZATION ON DATABASE::[DatabaseName] TO [PreferredOwnerLogin];. Choose the same dedicated, disabled, low-permission login recommended for the preferred owner check, since the same security reasoning applies: avoid using sa or any other privileged login as the new owner to prevent the db_owner privilege escalation path.
Investigate why the original owner login does not exist on the instance to determine whether the absence is expected or whether it points to a process gap. If the database was restored from another instance, confirm that the standard restore procedure includes the ownership reassignment step. If the original login was dropped intentionally, confirm that ownership was not transferred at the same time.
Update your standard restore, attach, and login removal procedures to include explicit ownership handling. Restores should reassign ownership to the preferred owner immediately after recovery, and login removals should reassign any owned databases before the login is dropped. These two steps together prevent unknown-owner conditions from accumulating in the future.