SQL Security Overview

This document provides a comprehensive overview of the security features and best practices for Microsoft SQL Server. Securing your SQL Server environment is critical to protect sensitive data from unauthorized access, modification, or destruction.

Key Security Pillars

SQL Server security is built upon several fundamental pillars:

Authentication: Verifying the identity of users or applications attempting to connect to the server.
Authorization: Granting appropriate permissions to authenticated principals, controlling what actions they can perform and what data they can access.
Data Protection: Implementing measures to protect data both in transit and at rest.
Auditing: Tracking and recording security-relevant events to detect and investigate suspicious activities.
Vulnerability Management: Regularly assessing and mitigating potential security weaknesses.

Authentication Methods

SQL Server supports two primary authentication modes:

Windows Authentication

This mode leverages the security infrastructure of Microsoft Windows. User accounts or groups are authenticated by Active Directory or local Windows accounts. This is generally the recommended authentication method for environments integrated with Windows.

SQL Server Authentication

This mode uses logins created directly within SQL Server, each with its own password. While simpler to set up in some scenarios, it requires careful password management and is generally considered less secure than Windows Authentication if not managed rigorously.

Authorization and Permissions

Once authenticated, SQL Server uses a robust permission system to control access:

Server-Level Permissions: Control access to server-wide resources and operations (e.g., creating databases, managing logins).
Database-Level Permissions: Control access to database objects such as tables, views, stored procedures, and functions.
Object-Level Permissions: Fine-grained control over specific actions on individual database objects.

Permissions are granted to security principals, which can be:

Logins (Windows users/groups or SQL Server logins)
Database Users
Roles (Database roles and fixed server roles)

Best Practice: Principle of Least Privilege

Always grant users and applications only the minimum permissions necessary to perform their required tasks. Avoid using overly broad permissions like `db_owner` for regular users.

Data Protection

Encryption in Transit

To protect data as it travels between the client and server, SQL Server supports encryption using Transport Layer Security (TLS), formerly known as SSL. This ensures that sensitive data cannot be intercepted and read by unauthorized parties on the network.

Encryption at Rest

SQL Server offers several features to protect data stored on disk:

Transparent Data Encryption (TDE): Encrypts the entire database files (data and log) at rest. It's transparent to applications, meaning no code changes are required.
Column-Level Encryption: Encrypts specific sensitive columns within a table.
Always Encrypted: A client-side encryption technology that keeps sensitive data encrypted at rest and in transit, with decryption performed only by authorized applications.

Auditing

SQL Server Audit allows you to monitor and audit database events, such as logins, failed logins, DDL statements, and DML statements. This is crucial for:

Compliance requirements
Investigating security breaches
Tracking data modifications

You can configure SQL Server Audit to send audit data to:

The Windows Security Log
The Windows Application Log
A specified file
The Windows Event Log

Vulnerability Management

Regularly assessing and addressing security vulnerabilities is essential:

Keep SQL Server updated with the latest service packs and security patches.
Use SQL Server Configuration Manager to disable unused services and features.
Regularly review and harden server configurations.
Employ security scanning tools to identify potential weaknesses.

Tip: Use SQL Server Management Studio (SSMS)

SSMS provides a graphical interface and tools to easily configure and manage most security features, including logins, users, permissions, encryption, and auditing.