SQL Server Security Administration

This documentation provides comprehensive guidance on securing your SQL Server instances. Security is paramount for protecting sensitive data.

Authentication Methods

SQL Server supports two primary authentication modes:

  • Windows Authentication: Leverages Windows security principals (users and groups) for authentication. This is generally the recommended method for domain-joined environments.
  • SQL Server Authentication: Uses logins created directly within SQL Server. This requires careful management of passwords and is suitable for non-domain environments or specific scenarios.

Configuring Authentication Mode

You can configure the authentication mode using SQL Server Management Studio (SSMS) or Transact-SQL (T-SQL):


-- Using T-SQL to set mixed mode authentication
USE master;
GO
ALTER LOGIN sa WITH PASSWORD = 'YourStrongPasswordHere'; -- Change password
GO
ALTER SERVER CONFIGURATION SET MEMORY_OPTIMIZED TEMPDB_METADATA = ON; -- Example: unrelated setting for demo
GO
EXEC xp_instance_regwrite N'HKEY_LOCAL_MACHINE', N'Software\Microsoft\MSSQLServer\MSSQLServer', N'LoginMode', REG_DWORD, 2;
GO
-- Restart SQL Server service for changes to take effect.

Note: Mixed mode allows both Windows and SQL Server authentication. Setting it to '1' enables Windows Authentication only.

Managing Logins and Users

  • Create logins with strong passwords.
  • Grant the principle of least privilege: grant only necessary permissions.
  • Regularly review and remove unused logins.

Authorization and Permissions

Once a user is authenticated, authorization determines what they can do. SQL Server uses a granular permission system.

Database Roles

Use fixed and user-defined database roles to manage permissions efficiently. Common fixed roles include:

  • db_owner: Full control over the database.
  • db_datareader: Read access to all data.
  • db_datawriter: Write access to all data.

Server Roles

Server-level roles control administrative privileges on the SQL Server instance:

  • sysadmin: Full administrative control over the SQL Server instance.
  • securityadmin: Manages server logins and their properties.
  • serveradmin: Configures server-level settings.

GRANT, DENY, REVOKE

Permissions can be explicitly granted, denied, or revoked for logins and roles at various levels (server, database, schema, object).


-- Granting SELECT permission on a table to a specific user
USE YourDatabase;
GO
GRANT SELECT ON dbo.YourTable TO YourLogin;
GO

-- Denying DELETE permission
DENY DELETE ON dbo.YourTable TO YourLogin;
GO

-- Revoking permissions
REVOKE SELECT ON dbo.YourTable TO YourLogin;
GO
Best Practice: Avoid using DENY where possible, as it can override GRANT statements and lead to complex permission management. Prefer granting permissions directly or through roles.

Data Encryption

Protecting data both in transit and at rest is crucial. SQL Server offers several encryption features.

Always Encrypted

Always Encrypted allows sensitive data to be encrypted within SQL Server databases. The encryption and decryption of the data happen outside of SQL Server. This provides a strong separation between those who own the data and can see it, and those who manage the database.

Transparent Data Encryption (TDE)

TDE encrypts data files and log files at rest. When the database is attached or opened, TDE decrypts the data on the fly. TDE protects against the threat of detached database files or whole database backups being stolen.

Dynamic Data Masking

Dynamic Data Masking limits sensitive data exposure by masking it to non-privileged users. You can define masks on specific columns, and the data is dynamically masked when queried by users without specific permissions.

Column-Level Encryption

You can encrypt specific columns using the ENCRYPTBYKEY and DECRYPTBYKEY functions, providing granular control over data protection.

Auditing and Logging

Auditing provides a record of database events, helping with security investigations, compliance, and troubleshooting.

SQL Server Audit

SQL Server Audit allows you to create server audits and database audits. You can capture information about:

  • Logins and logouts
  • Access to data and schema changes
  • Changes to server and database roles
  • Permission modifications

Creating a Server Audit


USE master;
GO
-- Create a server audit specification
CREATE SERVER AUDIT AuditToLog
TO APPLICATION_LOG
WITH ( QUEUE_DELAY = 1000, ON_FAILURE = CONTINUE );
GO
CREATE SERVER AUDIT SPECIFICATION ServerSecurityAudits
FOR SERVER AUDIT AuditToLog
ADD (SUCCESSFUL_LOGIN_GROUP),
ADD (FAILED_LOGIN_GROUP),
ADD (DATABASE_OBJECT_CHANGE_GROUP)
WITH ( STATE = ON );
GO

Log Management

Ensure that audit logs and SQL Server error logs are regularly reviewed and retained according to your organization's policies.

Security Alert: Unauthorized access to audit logs can compromise security investigations. Ensure audit logs are stored securely and access is restricted.

Network Security

Securing the network communication between clients and SQL Server instances is vital.

SQL Server Browser Service

The SQL Server Browser service listens for incoming requests for SQL Server resources and provides information about SQL Server instances installed on the computer. Disable it if not explicitly needed.

Firewall Configuration

Configure Windows Firewall or network firewalls to allow connections only from authorized IP addresses and on the specific ports used by SQL Server (default: TCP 1433).

Enabling Encryption (SSL/TLS)

Configure SQL Server to enforce encrypted connections using SSL/TLS. This encrypts data in transit, protecting it from eavesdropping.

  1. Install an SSL certificate on the SQL Server.
  2. Enable forced encryption in SQL Server Configuration Manager.
  3. Configure clients to trust the certificate and connect using encryption.

Named Pipes and Shared Memory

While convenient, Named Pipes and Shared Memory protocols can be less secure in certain network configurations. Consider disabling them if not required or if using a secure network.