SQL injection (SQLi) is a code injection technique that exploits security vulnerabilities occurring in an application's database layer. The vulnerability exists when user input is incorrectly sanitized before being incorporated into SQL queries. This allows attackers to manipulate the database by injecting arbitrary SQL code.
SQL injection has been classified as the number one web application security risk by OWASP for over two decades. Despite being well-understood, it continues to plague applications ranging from small websites to enterprise systems. Understanding SQL injection is essential for any security professional.
💡 Always practice SQL injection techniques in authorized environments such as CTF challenges, vulnerable web apps (DVWA, WebGoat), or lab environments you control. Unauthorized testing is illegal.
Most web applications interact with databases using SQL queries. When a user submits data through a form field, URL parameter, or cookie, that data is often concatenated directly into a SQL query string without proper validation or sanitization.
In this example, the user-supplied 'id' parameter is directly concatenated into the SQL query. An attacker could manipulate this parameter to alter the query's behavior entirely.
⚠️ SQL injection can lead to complete database compromise, including data theft, modification, deletion, and in some cases, full server takeover through command execution.
| Impact Category | Description | Severity |
|---|---|---|
| Data Breach | Unauthorized access to sensitive data | Critical |
| Authentication Bypass | Login without valid credentials | Critical |
| Data Manipulation | Modify or delete database records | High |
| Command Execution | Execute OS commands on the server | Critical |
| Denial of Service | Crash the database or application | Medium |
Throughout this course, we will explore each type of SQL injection in depth, learning how to identify vulnerabilities, exploit them in controlled environments, and implement proper defenses to protect applications.
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