What Is SQL Injection (SQLi), and How Do I Prevent Attacks?

SQL injection (SQLi) is a type of cyberattack in which an attacker manipulates a web application’s input to execute unauthorized SQL commands on a database. These attacks exploit vulnerabilities in how applications handle user-supplied data. This allows attackers to access, modify, or delete sensitive information. In some cases, the hacker can even gain administrative rights to a database. 

Here we will provide a comprehensive look at SQL injection. We’ll break down the attack mechanisms, explore SQLi examples, and walk through practical prevention strategies, with a focus on PostgreSQL and EnterpriseDB (EDB) Postgres® AI tools. By understanding the risks and the safeguards available, database administrators and developers can better protect their applications and sensitive data from these dangerous, yet common, attacks. 

Understanding SQL injection (SQLi)

Web applications rely on SQL databases to store and retrieve information, from user accounts to transaction records. When an application fails to properly handle user input, attackers can inject malicious SQL commands directly into queries, compromising the database. 

These vulnerabilities occur when data is linked directly into SQL statements without proper validation or parameterization. Cybercriminals exploit these weaknesses to manipulate queries, gain unauthorized access to sensitive information, tamper with existing data, or destroy all server data. 

There are three main types of SQL injection: 

• In-band SQLi: In this simplest and most common type of SQLi, attackers use the same communication channel to launch the attack and gather results. For example, attackers can retrieve sensitive data directly through manipulated or modified input fields.
• Union-based SQLi: This technique uses the SQL UNION operator to combine malicious queries with legitimate ones. This allows attackers to extract data from other tables in the database.
• Error-based SQLi: This injection method relies on database error messages to gain insights about the database structure. Attackers intentionally trigger these errors to learn table names, column names, or other schema details, which can then be used to execute further attacks. 

Theoretical and real-world SQL injection examples

To better understand how SQL injection works, it’s helpful to look at practical examples. 

In-band SQLi

Imagine that a website login box asks for a username and a password. Normally, the site will check to see if the username and password match what’s stored in the database. If they do, you’re allowed in. With an in-band SQL injection, the attacker doesn’t enter a real username and a password. Instead, the attacker types something tricky into the username box, such as ‘admin’ or 1=1. 

When the website checks the login, it’s being told to log this person in if the username is admin or if 1=1. Since 1=1 is always true, the check passes every time, and the attacker is logged in, even though they didn’t enter the real password.

Union-based SQLi

Imagine a shopping website that lets you type a product name into a search box. You search for shoes, and the site shows you all the shoes from its product database. Instead of typing a normal search, an attacker types something such as shoes UNION show me all usernames.

While the site is supposed to only show product results, the word UNION tells the database to combine the normal product results with something else requested. Instead of just showing shoes, the attacker can force the site to also display sensitive information, such as the list of usernames, email addresses, or other hidden data. 

Because the attacker sees the extra information right on the website’s search results page, it’s called a union-based SQL injection. This is because the attack and the results are joined together. 

Error-based SQLi

To understand an error-based SQLi, imagine the following scenario:

A travel website has a search box where you type a flight number to see details. Normally, if you type 1234, it shows that flight’s departure time, gate, etc.

However, an attacker can type a weird input instead of a flight number, such as a single quotation mark or some broken input. When the website tries to look up the flight, the database gets confused because of the non-numeric symbol. Instead of saying the flight wasn’t found, the site accidentally shows a detailed error message. 

That error message might show too much information, such as: 

• The name of the database system
• The exact table or column names inside
• Clues about how the query is structured

With those details, the attacker learns how the database works behind the scenes, which helps them build stronger attacks. 

These examples illustrate that SQL injection can affect any application that fails to validate or parameterize user input. Even simple input fields, search boxes, and login forms are common pathways of attack. Understanding these scenarios helps developers anticipate vulnerabilities and implement robust protection methods. 

Specific examples

The examples above discuss the code cybercriminals can use to initiate an attack. However, let’s explore some specific, real-world examples of successful attacks. 

• 2017 Equifax data breach: This major breach impacted millions of customers. It was caused by an unpatched vulnerability susceptible to SQL injections, and it exposed sensitive data such as birth dates and Social Security numbers.
• 2013 and 2014 Yahoo attack: SQLi attacks on Yahoo exposed the email addresses, names, and passwords of all Yahoo user accounts. There were approximately three billion people impacted.
• 2014 Sony Pictures hack: A group used SQL injection and other techniques to steal internal communications, personal employee information, unreleased films, and executive pay. 

The risks of SQL injection attacks

SQL injection attacks pose serious threats to both organizations and their customers. The consequences can be severe and can cause reputational, legal, and financial damage. 

Reputational damage and financial implications

A successful SQL injection attack can result in stolen customer data, account takeovers, or unauthorized financial transactions. The fallout can be catastrophic for businesses and erode customer trust. This can lead to lost revenue, legal fees, and costly incident response efforts. 

Compliance impact

Organizations that handle sensitive personal or financial data are often subject to strict regulatory frameworks, including:

• General Data Protection Regulation (GDPR)
• Health Insurance Information and Accountability Act (HIPAA)
• Payment Card Industry Data Security Standard (PCI DSS)

A breach caused by SQLi can lead to compliance violations, hefty fines, and heightened scrutiny from regulatory bodies. 

Data breaches and exposure of sensitive information 

SQL injection can expose sensitive data, including user credentials, Social Security numbers, financial records, or proprietary business information. In addition to the immediate risk, exposed data can be sold on the dark web or used for further attacks, which can compound the damage. 

Given these risks, understanding SQL injection and implementing preventative measures is a critical part of database security. By being proactive, you can protect your organization and customers from breaches. 

SQL injection prevention techniques

Preventing SQL injection requires a combination of secure coding practices, database configurations, and monitoring tools. By addressing multiple layers of vulnerabilities, you can significantly reduce your risk of an attack. 

Parameterized queries and prepared statements

Using parameterized queries ensures that user input is treated as data rather than executable code. Prepared statements allow developers to define SQL templates with placeholders for user input. This eliminates direct concatenation or linking. 

Database audit logging and monitoring

You can continuously monitor database activity to detect suspicious queries or unusual access patterns. Audit logs provide a historical record that is critical for forensic analysis and regulatory compliance. 

Stored procedures

Encapsulating database logic within stored procedures allows controlled execution of SQL commands. By limiting direct access to tables and validating inputs within the procedure, you reduce the surface for injections. 

ORM frameworks with built-in SQL safety

Object-relational mapping (ORM) frameworks, such as Hibernate or SQLAlchemy, automatically handle query construction. When used correctly, this reduces the likelihood of SQL injection. Your developers must ensure that queries generated by ORMs are not overridden with raw SQL, which can be unsafe and vulnerable. 

Input validation and sanitization

Properly validating and sanitizing user input is essential. Allowlisting allows you to accept only certain characters. Instead of trying to identify and block malicious characters, you just accept characters and formats that are safe for a particular input field. 

For example, in a username field, you can allowlist alphanumeric characters. Any input that contains special characters will be rejected, which prevents attackers from injecting malicious payloads. 

You can also utilize escaping techniques: Modify user input by neutralizing or encoding special characters that a system can interpret as part of the SQL syntax. This prevents attackers from altering the query’s intended logic. 

Least-privilege access

Least-privilege access allows you to limit the database permissions and roles for any user. You can restrict them to only the information they need to carry out their job functions. By limiting access, you can reduce the impact of a compromised account or SQLi. 

Web application firewalls (WAFs) and monitoring tools

A WAF can detect and block SQL injection attempts in real time. Additionally, utilizing other monitoring tools in conjunction with firewalls adds an extra layer of defense beyond the application level. 

Regular security testing

Routine penetration testing and SQL injection test cases help identify vulnerabilities before attackers exploit them. You can use automated tools and manual reviews to ensure a comprehensive cybersecurity strategy. 

By implementing these prevention techniques, developers and database administrators can significantly mitigate the risk of SQL injection attacks. These methods can prevent unauthorized access to sensitive data, protect your reputation, and save you from costly legal fines. 

Using EDB Postgres AI to Secure Your Database

EDB provides a suite of tools and extensions for PostgreSQL that make preventing SQL injection easier and more effective. These capabilities extend beyond basic database protections and offer enhanced monitoring, auditing, and security. 

EDB Postgres AI Advanced Server (EPAS)

EPAS includes built-in security extensions that strengthen PostgreSQL’s native defenses. Its features include enhanced password policies, stronger role management, and session controls. These capabilities reduce the risk of unauthorized database access. 

EDB Postgres AI Security Pack

This toolkit delivers advanced auditing, fine-grained access controls, and protective policies that help ensure compliance with security standards. It also supports blocking risky SQL patterns before they execute. 

PostgreSQL Extension Support

EDB Postgres AI (EDB PG AI) supports PostgreSQL extensions that enhance database security, including:

• Pgcrypto for encryption and secure hashing of sensitive data
• Pgaudit for detailed auditing of SQL activity
• Plpgsql_check for static analysis of PL/pgSQL code to detect vulnerabilities
• Pg_stat_statements to track the planning and execution of all SQL statements executed by a server

EDB Postgres Insight

EDB Postgres Insight offers visibility into database health and performance, but it also flags unusual SQL activity, such as repeated failed login attempts or atypical query patterns. This activity may indicate an injection attack in progress. 

EDB Postgres AI Enterprise Manager

With automated health checks, alerting, and centralized monitoring, EDB PG AI Enterprise Manager helps administrators quickly identify potential security issues. These may include SQL injection attempts across all database instances. 

By leveraging EDB PG AI’s specialized security features, organizations can detect and block SQLi attempts. Our solutions can also help you maintain ongoing organizational compliance and resilience in high-traffic environments. 

Maintaining SQL injection resilience

SQL injection prevention is not a one-time task. Instead, it requires consistent and ongoing effort. Even with strong defenses in place, new vulnerabilities can emerge through code changes, third-party interactions, and evolving attack methods. Building resilience means making security part of your organization’s everyday operations, including:

• Keeping database software up to date: Regularly apply security patches and updates for extensions and applications. Attackers often target outdated software because known vulnerabilities are easier to exploit.
• Regularly conducting security audits and code review: Auditing both your database configuration and application code helps catch risky patterns before they can be exploited. Code reviews should verify that all database queries use parameterized statements and safe bindings.
• Employing continuous testing: Automated penetration testing tools can simulate SQL injection attempts and uncover vulnerabilities in staging environments. This approach helps teams fix problems before they reach production.
• Integrating security practices: Security should be part of the software development lifecycle from the start. This includes using secure coding frameworks, enforcing database permission limits, and performing automated security scans during builds.
• Educating developers and database administrators: Training teams on secure coding practices, parameter binding, and proper input validation ensures that everyone who builds or maintains your system understands their role.