SQL injection is a type of security vulnerability that occurs when an attacker is able to manipulate SQL queries in a way that was not intended by the application developer. This can happen when user input is not properly sanitized or validated before being incorporated into SQL queries.
Here's how SQL injection works:
Input Validation: When a web application takes user input and uses it to construct SQL queries dynamically, if the input is not properly validated or sanitized, it can allow an attacker to inject malicious SQL code.
Injection: An attacker can input specially crafted SQL code into forms or URL parameters, hoping to manipulate the SQL query being executed by the application.
Execution: If the application does not properly handle the user input, the injected SQL code can be executed by the database server along with the legitimate query.
Exploitation: Depending on the nature of the injected SQL code, the attacker can exploit the vulnerability in various ways, such as retrieving sensitive data, modifying or deleting data, or even executing administrative commands on the database server.
Example of a vulnerable SQL query:
SELECT * FROM users WHERE username = '$username' AND password = '$password';
If $username and $password are not properly sanitized and an attacker inputs something like:
' OR '1'='1
The resulting query becomes:
SELECT * FROM users WHERE username = '' OR '1'='1' AND password = '' OR '1'='1';
In this case, the condition '1'='1' always evaluates to true, so the query effectively ignores the original authentication check and returns all rows from the users table, allowing the attacker to bypass authentication.
Preventing SQL injection involves using parameterized queries or prepared statements, which separate the SQL code from the user input and ensure that input values are treated as data, not as executable code. Additionally, input validation and sanitization techniques should be employed to restrict and filter user input to only allow expected and safe values. Regular security audits and testing are also crucial to identify and mitigate potential vulnerabilities in applications.