SQL Server Security Best Practices

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While SQL Server is designed to be a secure database platform, following best practices for configuring, managing , and monitoring your SQL Server environment can significantly reduce your risk of costly breaches, downtime, and violations of data protection and privacy regulations such as GDPR, HIPAA, PCI DSS, and SOX. 

Below, we’re sharing the critical SQL Server security best practices to implement. You’ll learn about implementing robust access controls, regularly patching and updating software, conducting security assessments and more.

Harden the Windows Server where SQL Server Operates

Hardening the Windows Server operating system before installing SQL Server is one of the most critical security best practices. Attackers who gain access to the OS can copy your valuable database files to their server, where they can break passwords and encryption at their leisure. To learn how to strengthen your Windows Server, review these Windows Server hardening best practices.

Understand Common SQL Threats

Like any database management system, SQL Server is susceptible to threats that could compromise data integrity, confidentiality and availability. Common threats to be aware of include:

  • SQL injection attacks occur when malicious SQL code is injected into the input fields or parameters of a SQL query. This can enable attackers to execute commands or to steal sensitive data, modify database records or gain access to the underlying system.
  • Unauthorized access refers to exploiting weak authentication mechanisms or misconfigured access controls to gain entry into SQL Server instances or databases. Attackers may attempt to brute-force passwords, exploit default credentials or bypass access controls to gain elevated privileges or access sensitive data.
  • Database exploitation involves the exploitation of vulnerabilities in SQL Server or the underlying operating system to gain unauthorized access to or control over the database server. Attackers may exploit unpatched vulnerabilities, insecure configurations or weak encryption mechanisms to compromise the integrity or availability of SQL Server databases.
  • Privilege escalation occurs when attackers exploit vulnerabilities or misconfigurations to elevate their privileges in order to gain access to sensitive data or administrative functions on the database server.

Download the guide for the full list.

Install Only the Required SQL Database Components

You should limit the installation to just the components your database needs to perform its tasks. This approach reduces your attack surface area by eliminating components that could have security vulnerabilities. It also minimizes resource utilization by the database and simplifies administration by removing services and components that must be managed.

Below are some essential components to consider:

  • Database Engine Services — This is the core component of SQL Server responsible for storing, processing and securing data.
  • SQL Server management tools — Include SQL Server Management Studio (SSMS) or Azure Data Studio for managing and administering the SQL Server instance.
  • Integration services — If your applications require ETL (extract, transform, load) functionality, select Integration Services to enable SSIS package execution.
  • Full-text and semantic extractions for search — Enable this feature if your applications require full-text search capabilities.
  • Analysis services  — Choose this option if you need multidimensional or tabular data analysis services.

Limit the Permissions of Service Accounts According to the Principle of Least Privilege

Each SQL Server service runs under a specified account. Those service accounts should be configured based on the principle of least privilege, which states that each account should have the minimum permissions it needs to function. Those rights should be assigned using security groups, rather than directly, to improve accuracy and transparency. 

Best practices include assigning each service a separate account. That way, even if the account for one service is compromised or damaged, other services will still operate normally. For example, Active Directory (AD) managed service account (MSA) — This is the best option for two reasons. First, managed service accounts cannot be used to log on to a server, so they are more secure than domain user accounts. Second, you do not need to manually manage password resets for service accounts, which reduces the risk of account compromise.

Follow Firewall and Network Security Best Practices

You can further enhance the security posture of your SQL Server environment by implementing firewall and network security best practices, which can be found in the downloadable PDF.

Configure SSL to Encrypt SQL Data in Transit

Configuring SSL/TLS to encrypt SQL data in transit helps protect sensitive information from unauthorized access during communication between client applications and the SQL Server instance. You should obtain a server authentication certificate from a trusted Certificate Authority (CA) or create a self-signed certificate. The certificate should include the fully qualified domain name (FQDN) of the SQL Server computer as the Common Name (CN) or as a Subject Alternative Name (SAN). 

Test SSL/TLS encryption by connecting to the SQL Server instance from a client application using SQL Server Management Studio (SSMS) or another database client.

Turn Off the SQL Server Browser Service

The SQL Server Browser service eliminates the need to assign port numbers to instances. While enabling this service enables SQL admins and authorized users to discover database instances over the network, it also makes it possible for attackers to gain knowledge of the available SQL Server resources. 

When running a default instance of SQL Server, you should turn off the SQL Server Browser service or configure another port for it to use to communicate. Then restart the SQL Server instance service, test application and client connectivity to the SQL Server, and update your firewall rules to allow direct access to the SQL Server.

Understand SQL Server Roles

Server roles provide an easy way to delegate administrative privileges, but you must assign these roles carefully. Always follow the principle of least privilege when assigning roles to users. For example, if a user needs only to be able to shut down the server and end processes, they should be assigned the server admin and process admin roles; assigning them the sysadmin role would violate the principle of least privilege. 

Understand SQL Server Effective Permissions

Create containers (such as groups or roles) and assign them permissions to access resources. Then, make accounts of members of those groups of roles. Following this best practice will be easier to understand the effective permissions for each account. Moreover, simply by putting a user in the right groups or roles, you can easily assign the correct permissions to new hires, accurately modify permissions as a user’s role changes and remove a user’s permissions when they leave the organization. When multiple permissions are granted to a user through different roles or groups, SQL Server follows a hierarchy to determine the effective permissions. Generally, the most permissive permission prevails, but if any permissions are explicitly denied, that overrides any grants.

Use Strong Passwords for Database Administrators

Strong passwords are necessary for all database administrator accounts to make them resistant to brute-force attacks. Be sure to follow current password best practices for password length and complexity. 

Install SQL Server Updates Promptly

Both white-hat and malicious hackers are constantly discovering vulnerabilities and exploits in SQL Server. Microsoft releases several types of updates to fix them:

  • Hotfixes, also known Quick Fix Engineering (QFE), are released to solve problems ASAP. Due to the tight time constraints, hotfixes receive limited testing, so they should be applied only to systems known to have the specific issues they address.
  • Cumulative updates (CUs) are periodic releases of hotfixes with thorough testing.
  • Service packs (SPs) are collections of patches and fixes that have been adequately tested and can easily be installed as a single package.

The simplest way to keep SQL Server up to date is to enable automatic updates from Microsoft. Organizations with a solid change process should apply updates only after performing their own testing.

Understand SQL Server Authentication Options

SQL Server offers several options for authenticating users: 

  • Windows Authentication is recommended in environments where SQL Server and client applications are in a Windows domainUsers connect to the SQL Server using their Windows credentials and the SQL Server validates their identity. This provides a more secure and centralized authentication mechanism.
  • SQL authentication or mixed mode authentication requires users to provide an SQL server login ID and password when connecting to the SQL server. User credentials are stored in SQL Server's security system rather than managed by Windows; this provides flexibility for environments where Windows authentication is not feasible. If you use this authentication mode to connect to SQL Server, do not use the SA account since it is the first account attackers will try to compromise in a brute-force attack.
  • Microsoft Entra authentication (introduced in SQL Server 2022) allows users to connect to SQL Server using their Entra ID identities. It provides centralized identity management and integrates with Azure AD's security features, such as conditional access and multifactor authentication. It requires the SQL Server to be configured for Azure AD authentication and for users to be synchronized with Azure AD. Microsoft Entra authentication supports Azure SQL database, Azure SQL managed instance, SQL Server on Windows Azure VMs, Azure Synapse Analytics and SQL Server.

Control Password Options for Logins

In a Windows environment, administrators can enable policies that control user password complexity and expiration. 

Be Diligent about Disabling and Deleting Logins

If a login will not be used for longer than one month, it should be disabled for the interim and then re-enabled. Regularly review all logins and deleted any that have been disabled for more than one year.

Back Up Your Databases

Backups help ensure that data can be recovered in case of system failure. Full backups back up the entire database, while differential backups back up only the changes since the last full backup. Differential backups are much faster and occupy less disk space than full backups, so they are especially useful for large databases. However, full backups should still be taken periodically. For small databases, the best practice is to use full backups every time. You can also take file and filegroup backups, which back up only specific files or filegroups. This strategy can reduce backup time and speed recovery of a single file or filegroup. However, be aware that managing filegroup backups can be complex. 

Monitor and Alert on SQL Server Activity

Effective monitoring is critical to detecting, diagnosing and resolving problems. For example, you might be able to identify long-running queries that could be malicious using SQL monitoring tools. In addition, configure alerts and notifications to proactively notify administrators about critical events, performance issues and system failures. You can use SQL Server Agent alerts, Database Mail or external monitoring systems to send alerts via email, SMS or other communication channels.

Mitigate the Risk of SQL Server Concurrency Issues

Concurrency issues in SQL Server include deadlocks and blocking. Deadlocks occur when two or more transactions wait for each other to release resources, so none of the transactions can proceed. Blocking occurs when one transaction holds a lock on a resource, preventing other transactions from accessing or modifying it. To identify and troubleshoot concurrency issues, monitor SQL Server performance metrics like locks, blocking and deadlock events using  tools like SQL Server Profiler, Extended Events and performance monitoring dashboards. Download the guide for additional strategies.

Baseline SQL Activity and Watch for Deviations 

Establish a baseline of normal behavior for your SQL Server instance, including CPU usage, memory utilization, disk I/O, locking and blocking events, query execution times, and other relevant performance indicators. Monitor these metrics to capture typical usage patterns and performance characteristics under normal operating conditions and establish threshold values. Be sure to periodically update the baselines and threshold values to account for changes in workload patterns, system configuration or database schema modifications.

Implement anomaly detection rules to identify deviations from the baselines. This can include simple threshold-based alerts or more advanced statistical methods for anomaly detection. Then investigate the root causes of the deviations, which can include attacks, resource contention and application issues.

Audit Access Attempts and Changes to Access Permissions

Enable login auditing in SQL Server and monitor the SQL Server error logs for information about failed and successful login attempts, as well as changes and deletions of database objects containing restricted data. 

In addition, track changes to SQL Server configurations and permissions so you can spot and remediate unwanted changes before you suffer significant damage. This tracking can be done using SQL traces or third-party software like Netwrix Auditor for SQL Server.

Enable SQL Server Audit

Enable the SQL Server Audit feature of SQL Server and specify the events to be audited, such as SELECT, INSERT, UPDATE, DELETE and EXECUTE. Configure audit log filtering to capture relevant events and minimize the volume of audit data generated.

For more granular information, use SQL Server Audit to capture database level events such as data access, schema changes and object modifications.

Mitigate SQL Injection Risks

SQL injection is a technique in which an attacker injects malicious SQL code into an application's input fields, forms or queries. As a result, they can steal or modify data, alter database schemas, execute resource-intensive SQL queries that overload the database server, deface websites, and hijack user sessions. 

Minimize the Risk of Side-Channel Attacks

In a side-channel attack, an adversary attempts to gather information or influence the execution of a system by measuring or exploiting its indirect effects, rather than targeting the system.  Download the guide for some strategies to minimize the risk of side-channel attacks.

Use Encryption Wisely

Encrypting data helps keep it secure even if unauthorized users access it, but encryption and decryption operations can introduce overhead and impact database performance. Evaluate the performance impact of encryption on your workload and optimize queries, indexes and server configurations to mitigate performance bottlenecks.

You can use several encryption features in SQL Server to protect your data:

  • Transparent data encryption (TDE) — TDE encrypts database files on disk, so it requires minimal changes to applications and queries. However, it does not protect data in memory or during transmission.
  • SQL column-level protection — The Always Encrypted option allows you to encrypt individual columns containing sensitive data, such as credit card details or Social Security numbers, while still allowing the database users to perform operations on the data. The data is encrypted in client applications before being sent to SQL Server and decrypted in the application after retrieval from SQL Server, ensuring the data remains encrypted both at rest and in transit.
  • SQL row-level protection — Row-level security (RLS) enables you to define security policies that specify which rows users can access based on user attributes, session context or other criteria, allowing fine-grained control over row-level access. You can also create indexes on a subset of rows in a table that meet specified filter criteria. SQL table views can also implement row-level security by limiting the rows returned to users based on their permissions. Triggers can enforce row-level security by intercepting data modification operations (e.g., INSERT, UPDATE, DELETE) and applying custom security logic.

Use Data Masking Techniques

SQL Server provides several data masking techniques to obfuscate sensitive information while preserving data integrity and usability for non-production environments. These techniques help prevent unauthorized access to sensitive data during development, testing or troubleshooting activities. 

The following are some common data masking techniques in SQL Server:

  • Dynamic data masking (DDM) masks sensitive data in real time based on user permissions without modifying the underlying data.
  • Static data masking permanently obfuscates sensitive data in non-production environments while preserving data relationships and characteristics. Static data masking can be applied to entire databases, specific tables or individual columns.
  • Hashing involves transforming sensitive data into irreversible hashed values using cryptographic hash functions such as SHA-256 or MD5. Hashing masks sensitive data by converting it into a fixed-length string that cannot be reversed to obtain the original value. While hashing helps protect passwords and other one-way encrypted data, it is unsuitable for preserving data usability in all scenarios.
  • Subsetting involves extracting a subset of data from a production database for non-production environments. During data extraction, you can use subsetting techniques to mask sensitive data by excluding or obfuscating specific rows or columns.
  • Tokenization replaces sensitive data with randomly generated tokens or placeholders while storing the original data in a secure vault. Tokenization allows you to preserve data relationships and usability while masking sensitive information. Tokenization is commonly used in payment processing and other applications where data security in SQL and compliance are critical.
  • Format-preserving encryption encrypts sensitive data while preserving its original format, such as maintaining the same data type, length and structure. FPE ensures that the masked data remains compatible with existing applications and databases without requiring extensive modifications. FPE techniques can encrypt credit card numbers, Social Security numbers and other structured data elements.

Choose Effective SQL Security Tools

For help in evaluating and improving the security posture of your SQL Server environment, consider the following Microsoft tools: 

  • Assessment and Planning Toolkit (MAP) is a free tool that helps organizations assess their SQL Server environment's readiness for migration, identify security vulnerabilities and generate reports with actionable recommendations. The assessment reports cover SQL Server versions, security configurations and compliance with best practices.
  • Secure Score for SQL Server is a feature of Microsoft Defender for SQL Server (formerly SQL Advanced Threat Protection). It analyzes SQL Server configurations, security settings and user permissions to identify potential security risks and provides actionable recommendations for improving security posture.
  • SQL Server Vulnerability Assessment (SSVA) is a feature of SQL Server Management Studio (SSMS) that helps identify security vulnerabilities in SQL Server databases. It performs automated checks against a predefined set of security best practices and recommendations, and provides detailed findings and remediation steps.
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