SQL Injection (SQLi)

SQL Injection is a vulnerability that allows an attacker to inject malicious SQL code into database queries through unvalidated input. One of the most common and dangerous web application vulnerabilities.

Types of SQL Injection

• In-band SQLi — result visible in response
• Blind SQLi — result not directly visible
• Out-of-band SQLi — data transferred via different channel

Example of Vulnerable Code

SELECT * FROM users WHERE username = '$username' AND password = '$password'

When entering ' OR '1'='1 the query becomes:

SELECT * FROM users WHERE username = '' OR '1'='1' AND password = ''

Protection

• Prepared Statements (parameterized queries)
• ORM frameworks
• Input validation
• Principle of least privilege for DB