How do you prevent SQL injection?

To prevent SQL injection, use parameterized queries (also called prepared statements) as your primary defense. Parameterized queries separate SQL code from user input by defining all SQL logic first and then binding data values to placeholders. This approach ensures user input is treated strictly as data, not executable code. For example, in Python using SQLite, instead of writing cursor.execute(f"SELECT * FROM users WHERE name = '{user_input}'"), you’d use cursor.execute("SELECT * FROM users WHERE name = ?", (user_input,)). The database engine automatically escapes special characters in user_input, neutralizing injection attempts. Most programming languages and frameworks (e.g., Java with JDBC, PHP with PDO) support this pattern, making it a universal solution.

Input validation and sanitization provide additional layers of protection. Validate user input against strict rules: reject invalid data entirely rather than trying to “fix” it. For instance, if a field expects a numeric ID, use server-side checks to ensure the input contains only digits. For text fields, whitelist allowed characters (e.g., alphanumerics and hyphens for usernames) using regular expressions. Avoid blacklisting “bad” characters like quotes or semicolons, as attackers often find ways to bypass these filters. Sanitization tools like PHP’s mysqli_real_escape_string() can escape dangerous characters, but this method is error-prone and should not replace parameterized queries. Always validate inputs before using them in SQL, even if they come from “trusted” sources like cookies or internal APIs.

Use additional safeguards to reduce attack surfaces. Object-relational mapping (ORM) libraries like SQLAlchemy or Hibernate automatically generate parameterized queries, reducing manual SQL string manipulation. Limit database permissions: application accounts should only have the minimum privileges required (e.g., SELECT/INSERT access without schema modification rights). Enable strict mode in your database to reject malformed queries. Regularly audit code for raw SQL concatenation and test inputs using tools like SQLMap. For legacy systems where rewriting queries isn’t feasible, employ Web Application Firewalls (WAFs) to filter suspicious payloads, but treat this as a temporary fix. Combining these practices creates a defense-in-depth strategy against SQL injection.