SQL injection exploits vulnerabilities in applications connected to databases by injecting malicious SQL code through user input fields like search boxes, login forms, and text fields.
SQL injection is extremely serious and ranks as one of the most critical web application security threats, consistently appearing at the top of the OWASP Top 10 list of web application vulnerabilities.
How SQL Injection Works
SQL injection attacks exploit insufficient input validation by inserting malicious SQL code through application input fields. Attackers leverage poorly designed input handling to transform user data into executable database commands. When an application fails to properly sanitize user input, attacker-supplied SQL code gets interpreted as part of the database query.
Attack Impact
Attackers can spoof identities, tamper with existing data, and cause repudiation issues such as voiding transactions or changing balances. Complete data disclosure, data destruction, or database server administration access all become possible through successful exploitation.
Attack Categories
Security experts classify SQL injection attacks into three primary categories based on how attackers extract information from compromised databases:
In-Band SQL Injection: The most straightforward approach where attackers use the same communication channel to launch attacks and retrieve results. This includes error-based SQL injection (using database error messages to extract information) and union-based SQL injection (using the UNION operator to retrieve data from other tables).
Inferential (Blind) SQL Injection: Attackers infer database structure and content without receiving direct data output. Boolean-based and time-based blind SQL injection techniques are used when the application does not return data directly but behaves differently based on true/false conditions.
Out-of-Band SQL Injection: Less common technique where attackers use different channels for attack execution and data retrieval, such as DNS or HTTP requests to external servers.
Prevention
Effective SQL injection prevention requires parameterized queries (prepared statements), stored procedures, input validation and sanitization, principle of least privilege for database accounts, and web application firewalls.