How SQL Injection Works

SQL injection is a common web security vulnerability that enables attackers to interfere with the queries an application makes to its database. By exploiting this, attackers can view, modify, or delete data they are not authorized to access, potentially compromising the entire database.

How SQL Injection Works

SQL injection occurs when an application directly concatenates user-supplied input into an SQL query without proper sanitization. Consider a typical login form where a user enters their username. The application might construct a query like this:

SELECT * FROM users WHERE name = ' + input + ';

If a legitimate user enters `admin`, the query becomes `SELECT * FROM users WHERE name = 'admin';`.

Injecting Malicious Code

An attacker can exploit this by entering a carefully crafted string into the input field, such as `' OR '1'='1`. When this input is directly inserted into the query, it transforms into:

SELECT * FROM users WHERE name = '' OR '1'='1';

Because `'1'='1'` is always true, the `OR` condition makes the entire `WHERE` clause evaluate to true for every row. This effectively bypasses any authentication logic, causing the database to return all rows from the `users` table, including sensitive information.

Preventing SQL Injection with Parameterized Queries

The most effective defense against SQL injection is to use parameterized queries (also known as prepared statements). With parameterized queries, the SQL command structure is defined separately from the actual data. The database engine then treats the user input purely as data, not as executable code.

For example, a parameterized query would look like this:

SELECT * FROM users WHERE name = ?;

The input `' OR '1'='1'` would be sent to the database as a literal string value for the `name` parameter. The database would then search for a user whose name is exactly `' OR '1'='1'`, which is highly unlikely to exist, preventing any malicious code execution.

Key Takeaways

• SQL injection exploits applications that directly embed user input into SQL queries.
• Attackers can manipulate query logic to bypass authentication or extract unauthorized data.
• Parameterized queries separate SQL code from user data, preventing injection.
• Always treat user input as untrusted and never concatenate it directly into database queries.