MySQL Tutorial
MySQL Installation and Configuration
MySQL Database Operations
Database Design
MySQL Data Types
MySQL Storage Engines
MySQL Basic Operations of Tables
MySQL Constraints
MySQL Operators
MySQL Function
MySQL Manipulate Table Data
MySQL View
MySQL Indexes
MySQL Stored Procedure
MySQL Trigger
MySQL Transactions
MySQL Character Set
MySQL User Management
MySQL Database Backup and Recovery
MySQL Log
MySQL Performance Optimization
SQL Injection is a code injection technique that attackers use to exploit vulnerabilities in a web application's database layer. Specifically, attackers can insert malicious SQL statements into an entry field for execution to manipulate the application's database directly. This can lead to unauthorized viewing of data, data manipulation, and even deletion.
For example, consider a login form with fields for username and password. The backend code might use these inputs in a SQL query like this:
query = "SELECT * FROM users WHERE username = '" + username + "' AND password = '" + password + "'";
An attacker could input something like anything' OR 'x'='x as the username or password. This would result in the following SQL query:
query = "SELECT * FROM users WHERE username = 'anything' OR 'x'='x' AND password = 'anything' OR 'x'='x'";
Since 'x'='x' is always true, this query would return all users, effectively bypassing the login mechanism.
How to Prevent SQL Injection:
Prepared Statements (Parameterized Queries): With prepared statements, SQL query execution is separated from the data itself. You define all the SQL code first, and then pass each parameter to the query later. This makes it impossible for an attacker to inject malicious SQL.
Stored Procedures: Like prepared statements, stored procedures separate data from the code and prevent an attacker from injecting malicious SQL.
Escaping User Input: This is not as secure as parameterized queries or stored procedures, but if you have to use dynamic SQL, you should always escape user input to ensure it's safe to use in a query.
Least Privilege Principle: Give your database user account the least amount of privilege necessary to perform its job. If your application only needs to perform SELECT queries, there's no need to give it DELETE permission.
Input Validation: Use a robust validation framework to validate user input for length, type, syntax, and business rules before accepting the data to be processed.
Web Application Firewall (WAF): A WAF can help filter out SQL Injection attempts.
Regularly update and patch: Ensure that all your systems, software, and applications are up-to-date with the latest patches.
Remember, the best way to prevent SQL Injection is to use a combination of these techniques. This way, even if one layer is breached, other layers of defense are still in place.
Parameterized queries to prevent SQL injection:
import sqlite3
username = input("Enter username: ")
password = input("Enter password: ")
conn = sqlite3.connect("your_database.db")
cursor = conn.cursor()
# Use parameterized query
cursor.execute("SELECT * FROM users WHERE username = ? AND password = ?", (username, password))
# Fetch results or perform further operations
conn.close()
Using prepared statements in SQL to prevent injection:
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
String username = "userInput";
String password = "userInput";
Connection connection = // Obtain connection
// Use prepared statement
String sql = "SELECT * FROM users WHERE username = ? AND password = ?";
try (PreparedStatement statement = connection.prepareStatement(sql)) {
statement.setString(1, username);
statement.setString(2, password);
try (ResultSet resultSet = statement.executeQuery()) {
// Process results
}
} catch (SQLException e) {
// Handle exceptions
}