Union-based SQL injection

 Introduction:

SQL injection is a technique that is used to exploit security vulnerabilities in web applications that use SQL databases. One of the types of SQL injection attacks is Union-based SQL injection. In this attack, the attacker uses the UNION operator to combine two or more SQL statements into a single statement, which can then be used to extract sensitive information from the database.

Where is the attack used?

Union-based SQL injection attacks can be used in any web application that uses SQL databases. These types of attacks are common on websites that accept user input, such as search fields, contact forms, and login forms.

Why use this attack?

The goal of a Union-based SQL injection attack is to extract sensitive information from a database, such as usernames, passwords, credit card numbers, and other personal information. Once the attacker has access to this information, they can use it for malicious purposes, such as identity theft or financial fraud.

Method of attacks:

The attacker begins by entering a malicious SQL statement into a form field or URL parameter. This statement is designed to retrieve sensitive information from the database. The attacker then uses the UNION operator to combine their malicious statement with a legitimate SQL statement that is already present in the application. This allows the attacker to retrieve the data they want without triggering any errors in the application.

To carry out a Union-based SQL injection attack, the attacker needs to know the structure of the database they are targeting. This information can be obtained through various means, such as using automated tools to scan the website or manually inspecting the source code of the application.

How to secure from this attack?

To prevent Union-based SQL injection attacks, web developers should use prepared statements or parameterized queries when accessing the database. These techniques ensure that user input is treated as data rather than code, making it more difficult for attackers to inject malicious code.

Additionally, web developers should sanitize user input to remove any potentially malicious characters, such as single quotes or semicolons. They should also limit the amount of information that is returned to the user, as this can help prevent attackers from extracting sensitive data from the database.

Types with explanation:

1. Error-based SQL Injection: This type of SQL injection is used to force the database to return an error message that contains sensitive information. The attacker can use this information to gain access to the database or to extract sensitive data.

2. Blind SQL Injection: This type of SQL injection is used when the attacker cannot directly see the result of their attack. Instead, the attacker uses Boolean logic to infer whether the attack was successful or not.

3. Time-based SQL Injection: This type of SQL injection is used to introduce a delay in the SQL statement. By measuring the time it takes for the server to respond, the attacker can determine whether the attack was successful or not.

Examples:

Here is an example of a Union-based SQL injection attack:

Suppose a web application has a search field that allows users to search for products by name. The application uses the following SQL statement to retrieve the products from the database:

sql
SELECT * FROM products WHERE name = '$search_term'

The attacker enters the following input into the search field:

sql
' UNION SELECT username, password FROM users--

This input causes the SQL statement to become:

sql
SELECT * FROM products WHERE name = '' UNION SELECT username, password FROM users--'

This statement retrieves the username and password from the "users" table and combines it with the results of the original SQL statement. The attacker can then use this information to gain access to the database or to extract sensitive data.