SQL injection is a type of security vulnerability that occurs when an attacker is able to insert malicious code into an SQL statement. The purpose of this injection is to manipulate the database and retrieve sensitive information, modify or delete data, or even take control of the entire system.
Here’s a simple example:
Suppose a website has a login page where users enter their username and password. The website uses the following SQL statement to check if the user’s credentials are correct:
SELECT * FROM users WHERE username = '$username' AND password = '$password';
If an attacker enters the following data as the username:
' OR '1'='1
The resulting SQL statement would be:
SELECT * FROM users WHERE username = '' OR '1'='1' AND password = '$password';
This statement would always return true, and the attacker would be able to log in without providing a valid password.
SQL injection attacks can be prevented by using prepared statements and parameterized queries, which separate the SQL code from the user-supplied data, making it much harder for an attacker to inject malicious code.