What Is SQL Injection And How To Prevent It?

What Is SQL Injection And How To Prevent It?

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Anshuman Singh
Senior Executive - Content
Updated on Feb 26, 2024 14:10 IST

Your website's got secrets? Hackers want them. SQL injection is like a pickpocket for your website, stealing info and causing chaos. But don't panic! This guide shows you how to lock your data tight and keep those villains out. Learn how to spot SQL injection and build unbreakable defences for your website. Take control, protect your secrets, and sleep soundly, knowing your data's safe.

What is SQL Injection and How to Use it?

So, precisely what is SQL Injection, and how do we prevent this attack? Before answering these questions, let’s go through the topics that we will be covering in this blog:

What is SQL Injection? 

SQL Injection (SQLi) is an injection attack that allows malicious SQL statements to be executed. In layman’s terms, SQL Injection attacks are a type of defect in the code of websites and web-based apps that allows cyberattacks to hijack back-end processes and access, edit, retrieve, and remove private information from your databases.

SQL injection attacks are one of web applications’ most prevalent, widespread, and destructive vulnerabilities. This attack can affect any website or web app that utilizes an SQL database, such as MySQL, Oracle, SQL Server, or any others. Criminals may exploit it to gain unauthorized access to confidential data, state secrets, intellectual property, and other information.

You can also explore: What is a Phishing attack?

How does SQL Injection work?

To understand the workings of SQL Injection, let’s use the help of an example. Suppose there are two database tables: Users and Contacts. The Users table could have fields such as ID, username, and password, and the Contacts table, can include various other fields, such as UserID, FirstName, LastName, Address1, Email, Aadhar number, etc.

You can also explore: What is a salami attack?

Users who want to log in will navigate to the login page and enter their password and username. This data is then transmitted to the web server, which creates an SQL query and sends it to the database server. An SQL query looks something like this:

Choose ID from Users where the username is 'Anshuman,' and the password is 'P@$$w0rD'.

SQL then performs a true or false comparison for every row the query requests. Because the database server fulfils that true-or-false check, we can trick it into thinking we have successfully authenticated by appending an OR (second condition) to the password. If we insert a second condition, such as the password for Anshuman is a’ or 5345 = 5345, we’ll get a new SQL query that looks like this:

Select ID from Users where username=’Anshuman’ and password=’a’ or 5345=5345

This will work because the database server will check the first condition. Is “a” the correct password for Anshuman, and if not, it will check the second condition. Is 5345 equal to 5345? As 5345 = 5345, the condition becomes true, and the user is successfully authenticated. An attacker can also merge two conditions, such as a’ or 5345 = 5345, with another condition like UNION SELECT LastName, Credit Card Number, etc. Additional clauses such as this may require additional work, but the main objective of an SQL injection attack is data access.

Types of SQL Injection 

SQL injections are of three types based on how attackers access backend data and the potential for damage. Those three types are:

In-band SQLi

In-band SQLi is among the most common SQLi attacks because of its simplicity and effectiveness. In this case, the attacker uses the same communication channel to launch attacks and collect data. There are two types of in-band SQLi: error-based SQLi and union-based SQLi.

The attacker in Error-based SQLi performs actions that cause the database to generate error messages. The attacker could potentially use the data these error messages provide to learn about the database’s structure. In contrast, the attacker in Union-based SQLi fuses multiple select statements generated by the database to obtain a single HTTP response. This response may contain information that the attacker can use.

Inferential SQLi or Blind SQLi

The attacker’s goal in this type of SQLi attack is to learn more about the server’s structure. To accomplish this, the attacker can send data packets to the server and examine its responses to gain knowledge about its structure. Because the data is not transmitted from the website database to the attacker, the attacker cannot see information about the attack in-band. Because of this, it is also called Blind SQLi. Inferential SQLi attacks are further classified into two types: boolean and time-based.

The attacker uses a boolean-type SQLi attack to send an SQL query to the database, triggering the application to revert a result. The outcome depends on if the query is true or false. The information in the HTTP response will change or remain unchanged depending on the outcome. With the help of the outcome, the attacker can determine whether the message produced a true or false result.

On the other hand, in the time-based SQLi attack, the attacker can send an SQL query to the database, which causes the database to wait for seconds before responding. The attacker can determine whether a query is true or false based on the database's response time. Depending on the outcome, an HTTP response will be generated immediately or later. The attacker can, therefore, determine whether the message they used returned a true or false value without depending on database data.

Out-of-band SQLi

This type of SQLi attack occurs when the attacker cannot use the same channel to launch the attack and collect information or when a server is too slow or unstable to perform these actions. The attacker can only perform the Out-of-band SQLi attack if certain features on the database server used by the web application are enabled. This attack acts as an alternative to in-band and inferential SQLi techniques.

You can also explore: What is a brute-force attack?

What are the consequences of a SQL Injection attack?

Some of the most common consequences of a SQL injection attack are:

  • Authentication bypass: If the app’s authentication form is defenceless to SQL injection, the user may log in without providing adequate login details.
  • Access to unauthorized data: SQL injection allows a user to access data that he is not authorized to see.
  • Unauthorized data manipulation: SQL injection can allow an application user to insert, modify, or delete data that he is not authorized to do. As a result, data integrity is jeopardized.
  • Gain admin privileges: SQL injection could allow an attacker to gain admin privileges on the database, thus allowing them to perform actions such as database shutdown.

You can also explore: What is two-factor authentication?

How to prevent SQL Injection attacks? 

Some of the ways that help you to prevent SQL Injection attacks are:

Continuous scanning and penetration testingAs SQL injections become more sophisticated in seeking to exploit logical errors. Website security professionals should consider manual testing with the assistance of a security vendor. They can validate the user’s input against even a set of syntax, type, and length rules. It is beneficial to audit security flaws quietly so you can rework the code before hackers exploit it.

Restriction of privileges: Limiting the application’s privileges ensures that an attacker who gains access to the database via the application cannot make unauthorized use of specific data. The assignment of specific privileges to specific accounts aids in the prevention of blind SQL injection attacks.

Deploy a managed web application firewall: You can immediately deploy a managed web application firewall to mitigate SQL Injection attacks. It includes custom policies that instantly restrict any potentially malicious input and deny any data breach. 

Manage patches and updates actively: Organizations must stay updated on the latest patches and updates as soon as possible. For SQLi purposes, this involves keeping all web application software components up to date, including database server software, libraries, plug-ins, frameworks, and so on, to reduce the likelihood of an attacker exploiting vulnerabilities in applications and databases.

Deny extended URLs: SQLi attackers may also send excessively long URLs, causing the server to fail to log the entire request. Another example is Microsoft IIS, which handles requests more significant than 4096 bytes. The web server software, however, fails to log the contents of the request. Attackers can then remain undetected while conducting queries. So, it’s better to set a limit of 2048 bytes for URLs to avoid such issues.

You can also explore: What is safe browsing and how to turn it on?


Common SQL injection attacks lead to knowledge loss or access denial. However, over time, hackers have combined such attacks with inadequate authentication, DNS hijacking, XSS, and DDoS to cause significant financial losses and complete host takeover. So, rather than being sorry later, use the above-mentioned preventive measure!


What are the potential consequences of a SQL injection attack?

A successful attack may result in the attacker gaining administrative rights to a database, viewing unauthorized user lists, deleting entire tables, etc.

What are the most common causes of SQL injection attacks?

The combining of data and code in dynamic SQL statements, error revelation, and insufficient input validation are the three root causes of SQL injection vulnerabilities.

How can SQL injection attacks be identified?

SQL Injection can be identifiedu00a0using methods such as reviewing server logs or monitoring database errors.

Which SQL injection attack is the simplest to execute?

The most common and easiest-to-exploit SQL Injection attack is in-band SQL Injection.

SQL injection is what kind of vulnerability?

SQL injection (SQLi) is a web security flaw that allows an attacker to interfere with database queries made by an application.

What is the most widely used SQL injection tool?

SQLMap is the most widely used SQL injection tool. This tool simplifies exploiting a web application's SQL injection vulnerability and taking over the database server.

What are some of the most popular SQL Injection tools?

Some popular SQL Injection tools include: Netsparker SQLMap jSQL Injection Blisqy Havij Burp

About the Author
Anshuman Singh
Senior Executive - Content

Anshuman Singh is an accomplished content writer with over three years of experience specializing in cybersecurity, cloud computing, networking, and software testing. Known for his clear, concise, and informative wr... Read Full Bio