SQL Security: Authorization

Authorization in SQL Server is the process of granting or denying permissions to users and roles, controlling what actions they can perform on database objects. This ensures that data is accessed and manipulated only by authorized individuals.

Key Concepts in SQL Authorization

Logins vs. Users

In SQL Server, a login is associated with the server instance, allowing access to the server itself. A user is associated with a specific database and is linked to a server login, granting permissions within that database.

Permissions

Permissions are the granular rights granted or denied to principals (logins or users) on securable objects. These can range from:

• Server-level permissions: e.g., ALTER SETTINGS, CONNECT SQL
• Database-level permissions: e.g., CREATE TABLE, SELECT, INSERT
• Object-level permissions: e.g., SELECT on a specific table, EXECUTE on a stored procedure.

Securables

Securables are the objects on which permissions can be granted or denied. These include:

• Server-level: Server itself, endpoints, logins, server roles.
• Database-level: Databases, schemas, roles.
• Schema-level: Tables, views, stored procedures, functions, types.

Managing Authorization

Granting Permissions

Permissions are typically managed using the GRANT statement. For example:

GRANT SELECT ON dbo.Customers TO db_readonly_role;
GRANT EXECUTE ON dbo.usp_UpdateProduct TO application_user;

Revoking Permissions

To remove previously granted permissions, the REVOKE statement is used:

REVOKE INSERT ON dbo.Orders TO reporting_user;

Denying Permissions

The DENY statement explicitly prevents a principal from performing an action, even if they are a member of a role that has been granted the permission. Deny permissions always override grant permissions.

DENY DELETE ON dbo.Products TO guest_user;

Roles

Roles are collections of permissions that can be assigned to users. This simplifies permission management by grouping related rights. SQL Server provides:

• Fixed Server Roles: Predefined roles with specific server-level permissions (e.g., sysadmin, serveradmin).
• Fixed Database Roles: Predefined roles with specific database-level permissions (e.g., db_datareader, db_datawriter, db_owner).
• User-Defined Roles: Custom roles created to group specific permissions tailored to application needs.

Best Practices

• Grant permissions using the principle of least privilege.
• Use roles extensively for efficient management.
• Avoid granting sysadmin or db_owner roles unless absolutely necessary.
• Regularly review permissions.
• Utilize Windows authentication where possible for centralized management.