SQL Server Security

SQL Server Security Model Overview

SQL Server security consists of two primary aspects: authentication and authorisation. Authentication is the process of verifying the identity of a user, while authorisation determines the permissions assigned to the user. By implementing proper authentication and authorisation mechanisms, you can ensure that only authorised users have access to sensitive information and perform specific actions within your database system. In this section, we will cover various authentication methods and authorisation mechanisms in SQL Server.

Authentication Methods for SQL Server

SQL Server provides two main authentication modes, which are:

• Windows Authentication
• SQL Server Authentication

Authorisation and Permissions

Once a user is authenticated, SQL Server uses an authorisation mechanism to determine the user's permissions. Authorisation in SQL Server is based on:

• Principals
• Securables
• Permissions

Permissions can be granted, revoked, or denied for specific principals and securables, allowing fine-grained control over who can access and manipulate the data stored within the SQL Server.

SQL Server Security Features

SQL Server offers various security features that help protect your data through encryption, certificates, and auditing options. These features enable you to create a robust security framework and enhance overall database security.

Encryption and Certificates

Encryption is the process of converting data into an unreadable format to prevent unauthorised access. SQL Server supports multiple encryption technologies, including:

• Transparent Data Encryption (TDE)
• Column-level Encryption
• Always Encrypted

Certificates play a crucial role in encryption, as they contain public and private keys used for encrypting and decrypting the data. SQL Server provides a comprehensive certificate management system to create, store, and manage certificates used for encryption.

Auditing Options

Auditing is the process of tracking and monitoring activities within your SQL Server to maintain security, ensure compliance, and investigate potential threats or incidents. SQL Server offers the following auditing options:

• SQL Server Audit
• C2 Audit Tracing
• Common Criteria Compliance

By utilising the powerful security features in SQL Server, you can create a reliable and secure database environment that meets your data protection needs and complies with industry-specific regulations.

SQL Server Security Best Practices

Applying best practices in SQL Server security helps minimise risks, maintain compliance, and protect valuable data from unauthorised access or potential threats. These recommendations ensure your SQL Server environment stays secure and robust.

Protecting SQL Server Instances

Protecting your SQL Server instances involves various activities such as performing regular updates and patches, using secure configuration settings, and monitoring for threats to safeguard your databases.

Regular Updates and Patches

Staying up-to-date with SQL Server updates and security patches ensures that your system benefits from the latest security enhancements and bug fixes. Microsoft regularly releases patches to address vulnerabilities, improve performance, and provide additional features.

• Subscribe to the Microsoft Security Updates to stay informed about the latest security patches and updates.
• Schedule regular maintenance windows to apply updates – consider balancing between immediate security fixes and potential system downtime.
• Test the updates in a non-production environment before deployment to ensure compatibility and minimise the risk of system outages.
• Monitor the performance and stability of your SQL Server instances to detect any unexpected issues resulting from the applied updates.

Secure Configuration Settings

Applying secure configuration settings in SQL Server further strengthens your security posture. Assess and modify the SQL Server configurations to reduce vulnerabilities and enhance overall instance security:

• Minimise the surface area – disable unneeded services, features, and components that could expose potential attack vectors.
• Configure appropriate authentication modes – prefer Windows Authentication or use Mixed Mode only when necessary, ensuring strong password policies are in place for SQL Server accounts.
• Limit SQL Server administrator privileges – restrict administrative access to only trusted users who require the highest level of access.
• Encrypt sensitive data – use encryption options such as TDE, Column-level Encryption, or Always Encrypted to protect your data at rest and in transit.
• Enable security and system monitoring – utilise SQL Server Audit and other monitoring tools to promptly identify potential security incidents or vulnerabilities.

Integrated Security in SQL Server

Integrated Security refers to the seamless and secure integration of SQL Server with the Windows operating system and its security mechanisms, leveraging the capabilities of Windows Authentication for your databases.

Benefits of Integrated Security

Implementing Integrated Security offers numerous advantages, leading to a more secure and manageable SQL Server environment:

• Enhanced security – Windows Authentication provides stronger security mechanisms by leveraging Kerberos or NTLM, mitigating the risk of replay and eavesdropping attacks.
• Simplified management – reducing additional username and password management, as users can use their Windows credentials to access SQL Server instances.
• Centralised account management – Active Directory integration enables centralised user and group management, simplifying the assignment and revocation of access permissions.
• Auditing and monitoring – user activities can be tracked using their domain account, ensuring greater accountability and traceability of actions within the SQL Server environment.
• Compliance – meeting regulatory requirements that demand strict access control and the use of secure authentication methods.

Implementing Integrated Security

To implement Integrated Security in your SQL Server environment, follow these steps to configure Windows Authentication and synchronise SQL Server with Active Directory:

1. Set the SQL Server instance to use Windows Authentication mode by modifying the "server authentication mode" property in SQL Server Management Studio (SSMS).
2. Create Windows user accounts or groups in Active Directory for users who need access to the SQL Server instance.
3. Add the Windows user accounts or groups to the SQL Server instance as logins using SSMS, granting the appropriate permissions based on the least privilege principle.
4. Assign the logins to appropriate database users and database roles within each database, controlling access to securables such as tables and stored procedures.
5. Configure your client applications to use Windows Authentication when connecting to the SQL Server instance, either by specifying "Integrated Security=true" or "Trusted_Connection=yes" in the connection string.
6. Regularly review and update user access, ensuring that only authorised users have access to the system and minimising potential security risks.

By following these best practices and implementing Integrated Security, you can significantly improve your SQL Server security, protect your data, and maintain a robust and compliant database environment.

Advanced SQL Server Security Techniques

In addition to the fundamental security practices, SQL Server offers advanced techniques to further protect your data and ensure that only authorised users access the information they need. These advanced techniques entail Row Level Security and advanced security features such as data masking, encryption, and Azure Active Directory integration for authentication.

Row Level Security in SQL Server

Row Level Security (RLS) is a powerful security feature in SQL Server that enables you to define granular access control for data rows within a table. By implementing RLS, you can control which users can view or modify specific rows, based on security predicates, ensuring that users can only access the data relevant to their roles or responsibilities.

Implementing Row Level Security

To implement RLS in SQL Server, follow these steps:

1. Create a security predicate function: This is a user-defined, inline table-valued function that returns a Boolean value (1 or 0) for each row, determining whether a user has access to that row. The function typically contains logic evaluating the user's access rights or user-specific attributes.
2. Create a security policy: This is a database object that binds the security predicate function to a specific table and defines the access control behaviour using filter predicates (for row visibility) and block predicates (for restricting data modification).
3. Activate the security policy: Enable the security policy, allowing it to take effect and enforce RLS on the table.

-- Create security predicate function
CREATE FUNCTION dbo.SecurityPredicateFunction(@EmployeeID INT)
RETURNS TABLE
WITH SCHEMABINDING
AS
RETURN SELECT 1 AS [AccessGranted]
FROM dbo.EmployeeAccess
WHERE EmployeeID = @EmployeeID AND UserName = USER_NAME();
GO

-- Create security policy
CREATE SECURITY POLICY dbo.RowLevelSecurityPolicy
ADD FILTER PREDICATE dbo.SecurityPredicateFunction(EmployeeID) ON dbo.Employees,
ADD BLOCK PREDICATE dbo.SecurityPredicateFunction(EmployeeID) ON dbo.Employees;
GO

-- Enable security policy
ALTER SECURITY POLICY dbo.RowLevelSecurityPolicy WITH (STATE = ON);
GO

Use Cases and Limitations

Row Level Security is particularly beneficial for:

• Multi-tenant applications: Segregate data based on tenant or customer, ensuring that users only access their own data.
• Confidential data: Restrict access to rows containing sensitive information such as financial records, medical data, or personally identifiable information (PII).
• Regulatory compliance: Enforce data access control for compliance with regulations such as GDPR, HIPAA, or PCI DSS.

However, RLS has certain limitations:

• Performance impact: As the security predicate function is executed per row, RLS can lead to increased query execution times if not optimised carefully.
• Schema changes: When altering the table schema, you may need to modify the security predicate function and security policy to accommodate the changes.
• Elevation of privileges: Users with elevated privileges, such as database administrators, may still view or modify data, necessitating additional security measures, such as data encryption or auditing.

Advanced Security Features in SQL Server

SQL Server offers a multitude of advanced security features that cater to specific data protection requirements. These features include data masking, encryption, and authentication using Azure Active Directory.

Data Masking and Encryption

Dynamic data masking is a technique that helps secure sensitive data by obfuscating it for unauthorised users, without changing the underlying data. This means, when a user without masking permissions queries the data, they receive masked results. SQL Server supports two types of dynamic data masking:

• Default masking: Replaces character data with "x" and numeric data with "0".
• Custom masking: Uses custom expressions to define the masking pattern.

To implement data masking in SQL Server, modify the table schema and define masking rules for the specific columns you want to protect. Additionally, assign the UNMASK permission to authorised users who need access to the original data.

While data masking provides limited protection by obfuscating the data, if you require stronger guarantees, consider using data encryption solutions such as Transparent Data Encryption, Column-level Encryption, or Always Encrypted.

Using Azure Active Directory for Authentication

Azure Active Directory (AAD) is Microsoft's cloud-based directory and identity management service that offers many benefits over traditional on-premises Active Directory, such as flexibility, scalability, and easy integration with other cloud services.

To use AAD for SQL Server authentication:

1. Provision an Azure Active Directory administrator for your SQL Server instance, linking it to your AAD tenant.
2. Create AAD users and groups, and grant them access to the SQL Server instance by adding them as logins and assigning appropriate permissions.
3. Utilise the "Active Directory Universal Authentication" option in your client applications and specify the AAD tenant when connecting to the SQL Server instance.

Azure Active Directory offers enhanced security features such as Multi-Factor Authentication (MFA), Conditional Access policies, and comprehensive auditing and monitoring capabilities that you can leverage to bolster your SQL Server security.