Understanding Database Roles and Permissions in SQL Server to Restrict User Creation and Management

Understanding Database Roles and Permissions in SQL Server

SQL Server provides a robust security model for managing access to databases. One key component of this model is the concept of database roles, which define a set of permissions that can be applied to users or other roles within the database. In this article, we’ll delve into the world of database roles and explore how to restrict the creation, alteration, and dropping of other users from the database.

What are Database Roles?

In SQL Server, a database role is a collection of permissions that define what actions can be performed on an object within the database. For example, the super_users role has been created with a set of permissions that allow it to select, alter, update, execute, insert, delete, create views, and create tables on a specific database.

Understanding the Problem

The user who owns the user_1 login is able to delete or drop other users from the database despite having been granted the super_users role. This behavior seems counterintuitive, as one would expect that owning the role should grant them full control over the permissions defined within it.

Understanding the Issue

The problem lies in the fact that SQL Server distinguishes between two types of privileges: granting and revoke.

When a user is granted permission to perform an action on an object, they are given explicit rights to do so. However, when you revoke control over an object, you are only removing your own permissions from it, not those that may have been previously granted to other roles or users.

In the case of the user_1 login, their permissions were initially granted as part of the super_users role. While the REVOKE CONTROL statement is used to remove the user’s own control over the object, it does not remove the grants that may have been previously made to other roles or users.

Deny vs Grant

To restrict the creation, alteration, and dropping of other users from a database, you need to understand the difference between DENY and GRANT.

When you use the GRANT statement, you are explicitly allowing a user or role to perform certain actions on an object. However, when you use the DENY statement, you are explicitly preventing a user or role from performing those same actions.

In SQL Server, it is not possible to revoke control over an object by name alone. Instead, you need to use the DENY statement along with the specific permission being denied.

Restricting Permissions using DENY

To restrict the creation, alteration, and dropping of other users from a database, we can use the following script:

DENY ALTER ANY USER,ALTER ANY ROLE,CREATE ROLE TO super_users;

This statement denies the user_1 login permission to create, alter, or drop other users within the super_users role.

Best Practices

Here are some best practices for managing database roles and permissions:

Always use explicit grants rather than relying on default permissions.
Use the DENY statement when possible to prevent users from performing certain actions.
Regularly review and update your database role assignments to ensure they remain relevant.

Additional Considerations

There are additional considerations that must be taken into account when managing database roles and permissions:

Role hierarchy: Roles can have a hierarchical relationship, where one role is subordinate to another. This allows for fine-grained control over permissions.
Login vs User: There is a distinction between logins and users in SQL Server. Logins are the identity of a user that connects to the database, while users are the objects within the database.
Object-level permissions: Permissions can be granted at the object level (e.g., table, schema) rather than at the role or login level.

Conclusion

Managing database roles and permissions is an essential part of maintaining security in SQL Server. By understanding the difference between granting and revoking control, using DENY statements to restrict permissions, and following best practices, you can ensure that your users are granted only the necessary permissions to perform their jobs.