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Types of SQL Injection


What are the different types of SQL injection, and how should they influence your 2024 cybersecurity plan?

According to reports, the attempts against online customers through web app attacks grew by 300% in 2022 alone... and continue to persist today. The bulk of these are attributed to SQl injection.

Today, our team outlines what SQL is, the most common types of SQL injection cybersecurity professionals face, and how your organization can safeguard itself against these threats. Let's dive in:

What is SQL?

SQL is defined as a standardized language used to access and manipulate databases to build customizable data views for each user. They are utilized in order to execute commands like data retrieval, updates, and record removal.

SQL injection, also known as "SQLI", is a common attack vector that leverages malicious SQL code for backend database manipulation. The result? Permitting threat actors access to information that was not intended to be externally displayed; most commonly, this info includes, but is not limited to, user lists, sensitive organizational data, or customer details like banking information, email addresses, passwords, and more.

The impact SQL injection can have on organizations of all sizes (and across all industries) stretches the imagination: a successful attack utilizing SQL injection not only stops at gaining viewership to information, but, in the worst case scenario, often encompasses threat attackers gaining administrative rights to protected databases.

Although this attack vector can be used to target any SQL database, websites are the most frequent targets.

Common Types of SQL Injection

Most commonly, the bulk of SQL injection falls under one of three categories:

  • Classic SQLi, also known as "in-band" SQLi

  • Inferential SQLi, also known as "blind" SQLi

  • And out-of-band SQLi

SQL injection types can be classified depending on the methods used to access backend data (alongside their potential for damages.) Here are the basics on these three main categories of attacks:

In-Band SQLi

Wen in-band SQLi is being leveraged, the threat actor or actors in question leverages the same channel of communication to launch their attacks and to gather their results.

Due to this injection's simplicity and efficiency, it is usable by threat actors of various experience levels, making it the most common type of injection in 2024. The two sub-variations of this injection method are as follows:

  • Error-based SQLi: Using this method, the hacker executes actions that trigger the targeted database to generate error messages. From there, the hacker can leverage the data provided by these error messages to gather more in-depth information about the structure of the database they have hijacked

  • Union-based SQLi: Using this method, the hacker takes advantage of the UNION SQL operator, which combines multiple statements generated by the targeted database to generate one single HTTP response. This response can then be used by the hacker for malicious means

Inferential (Blind) SQLi

By leveraging the inferential SQLi technique, the threat actor in question will submit data payloads to the targeted server. From there, they can observe the response of the server to better learn how to break or hijack its structure.

And where does its other name, "blind", come from? Well, this method earned its title due to how data is not transferred from the website database to the threat actor when the technique is in use, making it so the hacker can't see in-band info. As such, inferential SQL injections rely on the response patterns of the server; however, just because their impacts are not as immediate doesn't mean they aren't equally as harmful as the other two injection categories.

Similarly to in-band SQLi, blind SQL injection sub-categories can be boiled down to the following:

  • Boolean: When using a boolean SQLi, the threat actor will submit a SQL query to the targeted database in order to prompt the app to return a result. The result will vary depending on whether the query is true or false

  • Time-based: In this technique, an SQL query will be sent to the intended target's database, which, in turn, forces the targeted database to wait before a reaction can be processed. In these precious few seconds, the threat actor will analyze how long the database takes to respond, as well as if the query clocked as true or false

Out-of-Band SQLi

Last but not least is out-of-band SQLi.

Primarily known as an alternative to both in-band and blind SQLi methods, threat actors generally only leverage out-of-band SQLi when a database touts specific features that prevent them from using the same channel to both launch a data breach and gather information from it.

Common server features that would prompt threat actors to turn to out-of-band SQLi include:

  • When a database has input validation, making it so illegitimate user inputs can be detected

  • When a web application firewall (WAF) is deployed in order to filter out common SQL

  • When a server is too slow for usual techniques to be leveraged

  • When a server is too unstable for usual techniques to be leveraged

Alongside continuous penetration testing to combat all types of SQL injection in 2024, our ethical hackers advise to conduct the following:

  • Include input validations by filtering all kinds of user input, especially the SQL queries, before executing them

  • Implement the principles of least privilege in all user accounts interacting with the database.

  • Scan web apps periodically

  • Take security measures by verifying all API functions associated with API schemas

FAQs About Types of SQL Injection

"What classification is SQL injection?"

Structured Query Language (SQL) is classified as a code injection attack, and is deemed as accessible for threat actors to leverage due to lack of programming skill needed to execute the query.

"What is an error-based SQL injection?"

In an error-based SQLi, the threat actor will submit SQL queries to the intended victim's database in order to trigger errors. Once the errors have been triggered, they will use them to glean information on the structure of the database in question. Depending on the level of security the database has, an error-based SQL injection by itself can be enough to enumerate a targeted database.

"What is an out-of-bound SQL injection?"

Out-of-band SQL Injection occurs when the result of the attacker’s activities is received using one or more channels (generally speaking, submitted to another server.)

"What is a time-based blind SQL injection?"

In a time-based SQL injection, the threat actor will send SQL queries to the database and force it to wait its general processing time before generating a response; this permits the threat actor to analyze both the response time and how the query is resulting.

"What is a boolean-based SQL injection?"

Boolean-based SQLi has the malicious hacker send SQL queries to the intended victim's database, then subsequently force the application in question to return a different result depending on whether the query returns as false or true. Depending on the aforementioned result, the HTTP response will either adjust or remain the same.

"What is the most common type of SQL injection?"

In-band SQL Injection is the most common and easy-to-exploit of SQL Injection attacks. In-band SQL Injection occurs when an attacker is able to use the same communication channel to both launch the attack and gather results.

"What are the five sub-languages of SQLs?"

The 5 sub-languages of SQL are defined as the following: DDL (Data Definition Language); DML (Data Manipulation Language); DQL/DRL (Data Query Language); DCL (Data Control Language); and TCL (Transaction Control Language)

"What are the three main categories of SQLs?"

Classic SQLi (also known as "in-band" SQLi), inferential SQLi (also known as "blind" SQLi), and out-of-band SQLi.


All common types of SQL injection remain a top threat against web apps for organizations of all sizes, across all industries.

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