Some questions are open-ended and difficult to address with exact requirements. Here’s one such question I was asked at a recent User Group Meeting: “In recent versions of SQL Server, we can create a user without login. What is the use of it?”
This is an excellent question! Let me try to answer it. However, I encourage you to add your insights to enhance the value of this explanation.
Answer
Let’s visualize a scenario. Consider an application that performs numerous operations, many of which are highly sensitive. Traditionally, applications were assigned specific roles with elevated permissions. When regular users logged in (non-system admins), they had limited permissions. However, the application itself required a username and password embedded in its code to connect to the database and perform its operations. This approach had several challenges:
- Developers could easily access the application’s credentials.
- If a developer left the organization or the password needed updating, parts of the application had to be modified.
- Developers could misuse the credentials to directly log in and perform unauthorized actions.
In earlier versions of SQL Server, application roles were used to address some of these issues. However, this was later replaced by the concept of creating a user without login.
How It Works
Now, let’s recreate the above scenario using this concept. Regular users log in to SQL Server with their own credentials (username and password). Once authenticated, they can access the application, which performs operations by impersonating the special user. This specific user is configured with additional permissions required for the application’s functionality but has no login of its own.
This setup ensures that:
- Regular users are limited to their own restricted permissions.
- Sensitive operations are executed only under the impersonation of the special user.
- Credentials of this special user are not accessible, reducing misuse risks.
To further enhance security, explicitly DENY VIEW DEFINITION permissions on the database. This makes it harder for unauthorized users to determine how the application interacts with the database or obtain additional permissions.
Caveats and Limitations
It’s important to note that this approach applies only to users with restricted permissions. If someone with System Admin privileges tries to exploit the system, these safeguards won’t be effective, as admins can access everything by design.
For further protection, implement additional auditing and policy-based management to monitor and prevent potential misuse. No single measure is foolproof against a determined attacker, but layered security makes exploitation more difficult.
A Call for More Scenarios
The example above illustrates just one use case. I’m certain there are many more scenarios where creating such a user is beneficial. I encourage you to share your ideas and experiences in the comments. Did I miss any important points? Are there other use cases for this feature?
Let’s collaborate and explore more about this topic together.
Reference:Â Pinal Dave (https://blog.sqlauthority.com), YouTube
