SQL Injection
SQL Injection is a web security vulnerability where an attacker inserts malicious SQL statements into an application's input fields, tricking the backend database into executing unintended queries that can expose, modify, or delete data.
Definition
SQL Injection is a web security vulnerability where an attacker inserts malicious SQL statements into an application's input fields, tricking the backend database into executing unintended queries that can expose, modify, or delete data.
Overview
SQL Injection occurs when user-supplied input is concatenated directly into a SQL query string without proper sanitization or parameterization. If an application builds a query like `SELECT * FROM users WHERE username = '" + input + "'`, an attacker can supply input such as `' OR '1'='1` to alter the query's logic, potentially bypassing authentication or extracting entire database tables. SQL Injection has consistently ranked among the most dangerous and prevalent vulnerabilities in the OWASP Top 10, and it can lead to data breaches, authentication bypass, and in severe cases full database or server compromise. Variants include classic in-band injection (where results are returned directly), blind injection (where the attacker infers results from application behavior), and out-of-band injection (using external channels to exfiltrate data). The standard defense is to use parameterized queries or prepared statements, which separate SQL code from user data so input can never be interpreted as executable SQL. Input validation, least-privilege database accounts, and web application firewalls provide additional layers of protection. Security teams routinely test for SQL Injection using tools like OWASP ZAP and Metasploit as part of Penetration Testing engagements, and the vulnerability class is covered in depth in courses like Web App Security OWASP.
Key Concepts
- Exploits unsanitized user input concatenated into SQL queries
- Can bypass authentication, exfiltrate data, or modify database contents
- Includes in-band, blind, and out-of-band injection variants
- Consistently listed among the OWASP Top 10 web application risks
- Prevented primarily through parameterized queries and prepared statements
- Detectable through static analysis, dynamic scanning, and manual penetration testing
- Affects any application layer that builds SQL queries from user input