What is SQL Injection and How Does it Work

SQL injection

To perform a SQL attack, an attacker inserts malicious SQL code, most often a database query, into a string that’s eventually executed by the database through a web application (e.g. a login form).

SQL injection works by taking advantage of poor validation and sanitization of the web application. Attackers can malicious SQL statements into user input fields, which then get executed by the database. This can lead to unauthorized access, data theft, and other malicious activities.

Potential Impacts of SQL Injection Attacks:

One of the main risks of SQL injection attacks is the of sensitive data. Attackers can use SQL techniques to retrieve usernames, passwords, credit card information, confidential data from the database. This can lead to loss of identity for individuals and organizations.

Additionally, SQL injection attacks can lead to database manipulation and corruption. Attackers can alter, delete, or insert malicious data, causing disruptions to business operations and compromising the integrity of the system.

SQL injection can generally be used to perform the following types of attacks:

  • Authentication Bypass
  • Insert, modify, or delete data.
  • Extracting data.
  • Denial of service to authorized users by locking or deleting database tables.

What is a Database?

A database consists of one or more tables. Each table is made up of rows and columns and contains information such as user ids, passwords, web page details…

Databases are used for storing, maintaining, and accessing any sort of data. They collect information on people, places, or things. There are many databases available like MySQL, Oracle, MongoDB, PostgreSQL, SQL Server, etc.

Types of SQL injection

Union based SQL Injection: This type of attack leverages the UNION SQL operator to combine the results of two or more SELECT statements. It allows an attacker to retrieve data from different database tables and can be used to extract sensitive information.

Blind SQL Injection: In a blind hack, an attacker exploits a vulnerability without receiving error messages or visible data. The attacker uses Boolean-based or time-based techniques to infer information from the application’s response, allowing them to determine if a particular condition is true or false.

Error based SQL Injection: Error-based attack involves injecting malicious SQL code that is designed to produce an error in the database. By analyzing the error message, an attacker can gain insights into the underlying database structure and potentially extract sensitive information.

Time based SQL Injection: In a time-based attack, an attacker injects malicious SQL code that introduces delays in the application’s response. By analyzing the variations in response times, an attacker can deduce information about the database and extract data.

Second order SQL Injection: This type of injection occurs when user input is stored in a database and later used in a query without appropriate sanitization. The stored input can be subsequently used in a vulnerable SQL query, leading to a successful injection attack.

SQL Injection Attack Examples

This example shows how an attacker can use injection to bypass login authentication and gain administrator privileges.

Consider a simple authentication login form using a database table with usernames and passwords. A user’s POST request will provide the variables user and pass, and these are inserted into a SQL statement:

SELECT * FROM users WHERE username =”John” AND password =”mypass”

The attacker can bypass the password field using the following statement:

SELECT * FROM users WHERE username =’John’ AND password=’mypass’ OR 1=1'

Because 1=1 is a condition that always evaluates to true, the entire WHERE statement will be true, regardless of the username or password provided.

The WHERE statement will return the username from the users table, which is commonly the administrator. This means the attacker can access the website without authentication and also has administrator privileges.

Retrieving Hidden Information

Consider a website that displays products in different categories. When the user clicks on the electronics category, their browser requests the URL:


This causes the application to make a SQL query to retrieve information from the database:

SELECT * FROM products WHERE category = ‘electronics’ AND released = 1

The restriction released = 1 is being used to hide products that are not released. An attacker can construct an attack like:


This results in the SQL query:

SELECT * FROM products WHERE category = ‘electronics’--‘ AND released = 1

The key thing here is that the double-dash sequence — is a comment indicator in SQL, and means that the rest of the query is interpreted as a comment. This means that all products are displayed.

Also, an attacker can cause the website to display all the products in any category, including categories that they don’t know about:


This results in the SQL query:

SELECT * FROM products WHERE category = ‘electronics OR 1=1 — ‘ AND released = 1

The query will return all items where either category is electronics. Since 1=1 is always true, the query will return all items.

How to avoid SQL injection

Preventive Measures against owasp SQL Injection: To prevent SQL injection attacks, developers and organizations should implement preventive measures, including:

Input validation and sanitization: Thoroughly validate and sanitize user input to ensure that it only contains the expected data types and does not include any malicious SQL code.

Use of prepared statements and parameterized queries: Utilize prepared statements and parameter queries instead of dynamically constructing SQL queries. This approach separates the SQL code from user input, significantly reducing the risk of SQL injection.

Implementation of the least privilege principle: Implement the principle of least privilege, database users are granted only the necessary permissions to perform their tasks. This the potential impact of an SQL injection attack.

Regular updates and patches for database systems: Keep the database systems up to date with the latest security patches and updates. This ensures that known vulnerabilities are fixed and protects against SQL injection attacks.

Escaping symbol characters is a simple way to protect against most SQL injection attacks.

To protect your website against SQL injection, you need to provide the mysql_real_escape_string function to escape special characters in a string before sending a query to MySQL.

For example, if you were to insert OR 1=1 as a password input to that query, a database client would not interpret that input as SQL or computer code. Instead, it would look for a password string OR 1=1.

How to prevent SQL injection attacks

To detect and mitigate SQL attacks, organizations can implement the following measures:

Intrusion detection systems fire: Utilize intrusion detection systems to monitor network traffic and identify any suspicious activity or  injection attempts.

Log monitoring and analysis: Regularly monitor and analyze log files for any signs of SQL attacks. Log analysis can help identify patterns and anomalies that indicate potential security breaches.

Web application security scanners: Use web application security scanners to scan application vulnerabilities, including SQL injection. These tools can automatically report potential weaknesses that could be targeted by attackers.

Real-time SQL injection attack detection techniques: Implement real-time detection techniques such as web application firewalls (WAFs) and Intrusion Prevention Systems (IPS). These systems can analyze incoming requests and block any suspicious injection attempts.

Best Practices for Securing Against SQL Injection:

To enhance the security posture against SQL injection attacks, organizations should follow these best developers about SQL risks: Provide comprehensive training and guidelines to developers on the risks of SQL attack and secure coding. includes validation parameters and error handling.

Adhere to secure coding practices throughout the software development lifecycle. This includes conducting code reviews, using secure development frameworks, and regularly updating libraries and dependencies.

Regular security audits and vulnerability assessments:  Perform regular security audits and vulnerability assessments to identify and remediate any SQL injection vulnerabilities. This ensures that the application and underlying systems remain secure.

Incident response and disaster recovery plan: Develop and maintain an incident response plan and a disaster recovery plan to minimize the impact of a successful SQL injection attack. This includes proper backups, system monitoring, and incident response procedures.

SQL injection attacks pose significant risks to web applications and databases. Understanding the working principles of SQL injection, its potential impacts, and effective preventive measures is crucial for organizations and developers to protect against these attacks.

Remember, staying updated with the latest security practices and continuously monitoring the system’s security posture is essential to defend against emerging SQL injection threats.


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