SQL Injection

What Is SQL Injection?

SQL injection is a method of injecting malicious code into input fields of a web application, making it one of the most dangerous threats. Attackers use this technique to manipulate databases into executing SQL commands, aiming to steal, modify, or disrupt sensitive data. To mitigate SQL injection attacks and enhance data security, the industry commonly employs Web Application Firewalls. These tools encrypt data, conduct security tests, and ensure timely patch updates.

What types does SQL Injection have?

Based on how attackers access the database, SQL injection can be categorized into three types :

• 1. In-band SQL injection refers to the attacker using the same communication channel to execute the attack and retrieve results. Common types include Error-based SQL injection and Union-based SQL injection. Error-based SQL injection is when the attacker uses special functions to exploit the database and relies on error messages from the database server to glean information about the database structure. Union-based SQL injection refers to attackers using the UNION SQL operator to merge multiple SELECT statements into one result, which is then returned as part of a single HTTP response containing the desired data.

• 2. Inferential SQL injection, also known as blind SQL injection, involves the attacker sending valid payloads to observe the web application's response and the resulting behavior of the database server, in order to infer and reconstruct the database structure. Unlike in-band SQL injection, the attacker does not receive immediate feedback on the success of the attack. Common types of inferential SQL injection include Boolean-based blind SQL injection and Time-based blind SQL injection. In Boolean-based blind SQL injection, the attacker sends an SQL query to the database and determines if the content in the HTTP response changes based on the result returned by the page. Time-based blind SQL injection, on the other hand, involves the attacker sending an SQL query to the database and inferring unknown fields by analyzing the response time of the page.

• 3. Out-of-band SQL injection occurs when the database server does not provide a stable response or when the attacker cannot use the same communication channel to execute the attack and retrieve results. In this scenario, the attacker injects malicious code to enable specific functions on the database and then sends data from the database to controlled computers in order to steal information. Common types of out-of-band SQL injection include DNS log-based blind SQL injection and HTTP header-based SQL injection. DNS log-based blind SQL injection involves the attacker using the domain name access function of an application to initiate a DNS request and extract data based on the blind injection result recorded in the DNS log. HTTP header-based SQL injection occurs when the attacker inserts additional HTTP request header fields to obtain genuine HTTP responses and steal database data.

What are the principles of SQL Injection?

SQL injection is an attack method that takes advantage of vulnerabilities in web applications. Attackers leverage this technique to craft dynamic SQL queries and inject malicious code into user input fields. This code deceives databases into executing SQL commands, leading to the compromise, alteration, or destruction of sensitive data, or even the execution of harmful system-level commands on database hosts. Since most websites and web applications rely on SQL databases, SQL injection attacks have become one of the oldest and most prevalent web attack vectors.