SQL injection is a code injection technique where an attacker inserts malicious SQL statements into input fields or URL parameters that are incorporated into database queries. If the application does not properly sanitize inputs, the injected SQL can read, modify, or delete data, bypass authentication, or even execute system commands.
SQL injection remains one of the most common and dangerous web vulnerabilities. The OWASP Top 10 consistently lists injection attacks among the most critical security risks. The attack exploits the practice of constructing SQL queries by concatenating user input with query strings, allowing attackers to alter the query's logic. Database security books on Amazon explain attack techniques and defenses.
For URL shortening services, SQL injection risks exist wherever user input interacts with the database: creating short URLs, looking up redirect destinations, querying analytics data, and managing user accounts. The primary defense is using parameterized queries (prepared statements) that separate SQL code from data.
Additional defenses include input validation, least-privilege database accounts, stored procedures, and web application firewalls. Modern ORMs and query builders typically use parameterized queries by default, but developers must remain vigilant against raw query construction. Application security books on Amazon cover defense-in-depth strategies.