What is SQL Injection?
SQL Injection Definition: SQL injection is a code injection technique that exploits vulnerabilities in database-driven applications by inserting malicious SQL statements into entry fields, tricking the system into executing unintended commands that can allow attackers to bypass authentication, access, modify, or delete data, compromising the database and potentially the entire system.
Understanding SQL Injection
SQL Injection is one of those security vulnerabilities that perfectly illustrates how simple coding oversights can lead to devastating consequences. At its core, it's an attack technique that exploits flawed input validation to trick a database into executing malicious SQL commands that were never intended by the application developers.
The vulnerability typically occurs when applications construct SQL queries by directly concatenating user input with SQL command strings. Imagine a login form where the application builds a query like: "SELECT * FROM users WHERE username = '" + userInput + "' AND password = '" + passwordInput + "'". When used as intended, this works fine. But what happens when a malicious user enters something like "admin' --" as their username? The resulting query becomes "SELECT * FROM users WHERE username = 'admin' --' AND password = '...'" where everything after the double dash is treated as a comment and ignored by the database. Suddenly, the attacker has bypassed password verification entirely.
More sophisticated SQL injection attacks can extract sensitive data from other tables, modify database contents, delete entire databases, or even gain access to the underlying operating system. What makes these attacks particularly dangerous is that they exploit the legitimate communication channel between the application and its database, making them difficult to detect through network monitoring alone.
The damage potential is enormous. In one infamous case, a major retailer suffered a breach where attackers stole data from 40 million payment cards through SQL injection. Another attack compromised hundreds of thousands of government databases by injecting malicious code that was automatically executed when administrators viewed the compromised data.
Fortunately, preventing SQL injection is straightforward with proper coding practices—using parameterized queries or prepared statements that separate SQL code from data, implementing proper input validation, employing least-privilege database accounts, and regularly testing applications with security scanning tools designed to identify such vulnerabilities.