SQL Injection Types: The 3 Most Dangerous Attacks (2023)

By Tibor Moes / Updated: June 2023

SQL Injection Types: The 3 Most Dangerous Attacks (2023)

SQL Injection Types

Imagine a friendly mailman who’s always on time, delivering your mail exactly as you expect. But what if, one day, a prankster convinces the mailman to deliver things to the wrong house, causing havoc in the neighborhood? SQL Injection operates in a similar way: by manipulating inputs, hackers can trick a system into delivering data where it shouldn’t.


SQL Injection is a hacking technique where attackers manipulate inputs to exploit vulnerabilities in a database, tricking it into sharing, modifying, or deleting sensitive data in ways it was not originally designed to do.

Type 1 – Union-Based SQL Injection: This is the cheeky guest who mixes up the party invite list, adding their friends. Hackers use the UNION SQL operator to combine their unauthorized data request with the legitimate one, causing the database to spill secrets it otherwise wouldn’t.

Type 2 – Time-Based Blind SQL Injection: Like a crafty thief testing a home’s security, hackers send queries that force the database to wait before responding. By measuring this delay, they can figure out valuable information, even without any data being explicitly returned.

Type 3 – Out-of-band SQL Injection: This is the elusive party-crasher who sneaks in, leaves with the silverware, and you only realize it when you’re doing the dishes. Instead of retrieving data directly, hackers manipulate the database to send its information somewhere else, where they can collect it unnoticed.

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SQL Injection Types In-depth

Union-Based SQL Injection: The Party Crasher Who Rewrites The Guest List

Think of the SQL database as a highly exclusive party, where everyone has been meticulously selected. The list of partygoers (your data) is carefully managed by the host (your application). Enter the ‘Union-Based SQL Injection,’ the sly character who knows how to sneak into your carefully planned party by rewriting the guest list.

The ‘Union’ part of this term might sound somewhat friendly, like the meeting of two equally respected parties, right? But don’t let the name fool you. In the world of SQL, ‘UNION’ is a command used to combine rows from two different tables, given that they have the same type and number of columns.

The party crasher (the hacker) uses this seemingly harmless command in a malicious way. They append a ‘UNION SELECT’ command to regular SQL queries made by your application, essentially rewriting your guest list. They craftily sneak in their own queries alongside your legitimate ones, convincing your system to return data it shouldn’t.

Just picture the following scene: you ask your butler (the application) for the list of guests (the data). But a mischievous gatecrasher has fooled the butler into including names you didn’t approve. Now, you end up with extra, uninvited guests at your party!

How do they achieve this? It’s all about the inputs. When your application asks users for information, these inputs are usually incorporated into SQL queries. For example, if a user is logging in, their username might be part of a query like ‘SELECT * FROM users WHERE username = [input].’ If the user types ‘John,’ then John’s data is retrieved. But what if, instead of ‘John,’ the user types ‘John’ UNION SELECT * FROM credit_card_info? Then, the system is tricked into returning data from an entirely different table!

Here’s the catch: Union-Based SQL Injection requires a bit of knowledge about your database structure. The hacker needs to know what tables exist and how they are designed. But given enough attempts, they can often figure this out through trial and error.

In our party analogy, this is like the gatecrasher knowing the layout of your house, enabling them to dodge security and navigate the crowd without causing a stir. It’s a deceptive, intrusive tactic that can lead to significant data leaks if not correctly managed.

To prevent this from happening, make sure your application never trusts user input blindly. Treat every input as if it’s an attempted gatecrasher. This means validating and sanitizing inputs, employing prepared statements or parameterized queries, and minimizing the error details exposed to users.

With careful measures, you can keep your ‘party’ exclusive and your data secure, ensuring that the ‘Union-Based SQL Injection’ remains an unwelcome outsider.

Time-Based Blind SQL Injection: The Stealthy Spy Testing Your Defenses

magine you’re living in a well-guarded fortress, complete with high walls, watchtowers, and heavily armed guards. In the world of databases, this fortress is your database, full of valuable treasures in the form of sensitive data. But what if a wily spy was testing your defenses, trying to sneak in without being seen? This scenario plays out in the digital world through the Time-Based Blind SQL Injection technique.

In the SQL universe, this is the James Bond of attack types. It’s not about brute force or charging in headlong; it’s all about patience, subtlety, and timing. The attacker isn’t actually “blind” in the sense they can’t see. Instead, it’s the system that’s blind to the intrusion.

Picture this: the spy – our SQL injection – is outside your fortress. They can’t see what’s inside, but they can send a homing pigeon (the SQL query) over the walls. Depending on how long it takes the pigeon to return (the database response time), they can start making educated guesses about what lies inside your fortress.

Here’s how it works. In a Time-Based Blind SQL Injection attack, a hacker manipulates the SQL query to include a command that forces the database to ‘pause’ or ‘wait’ before responding. By measuring this delay, the hacker can infer whether the condition in their injected SQL statement is true or false.

Say a hacker sends a query that includes the command “IF (username = ‘admin’) WAITFOR DELAY ’00:00:10′–“. If the username ‘admin’ does exist, the database will pause for 10 seconds before responding. If the delay isn’t there, then the hacker knows the statement was false – ‘admin’ doesn’t exist.

Time-Based Blind SQL Injection is like a game of digital 20 Questions, where each question takes time to answer. The attacker slowly gathers information, bit by bit, until they have enough to breach your defenses.

Guarding against this type of attack requires ensuring that user inputs are thoroughly checked and cleaned to prevent unauthorized SQL commands from being run. This involves techniques such as input validation, parameterized queries, and limiting database permissions.

Always remember, time is not just money; in the hands of a crafty attacker, time can be a powerful tool to glean sensitive information. So, fortify your defenses and be alert to those who might be playing the long game to infiltrate your database.

Out-of-band SQL Injection: The Artful Dodger of Data Theft

Let’s conjure up a vivid image to understand Out-of-band SQL Injection. Think of your database as a bustling marketplace, filled with precious goods (data). Each stall is a table, and the stall owners are your applications, responsible for selling (or rather, serving) these goods to customers (users).

Now imagine a slick pickpocket flits around your marketplace, not just swiping an apple here and there but persuading the stall owners to send boxes of goods to a far-off place. That’s Out-of-band SQL Injection – an elegant, roundabout way of extracting data.

‘Out-of-band’ might sound like a technical term from the high seas or the music industry. But in the world of SQL, it’s the method hackers use to get data delivered somewhere else, instead of taking it directly.

Here’s the trick: instead of trying to ‘read’ the data right on the spot (which might alert security), our digital Artful Dodger gets your database to send its information to an external server where they can peruse it at their leisure. They accomplish this by exploiting features that allow databases to make DNS or HTTP requests to external servers.

Consider this scenario: the hacker might insert a SQL command that instructs your database to fetch a DNS or HTTP URL. Unbeknownst to your system, this URL is owned by the hacker. The trick? The requested URL contains sensitive data from your database. When your database makes the request, it inadvertently sends the data straight to the hacker’s server, like a marketplace stall owner unwittingly delivering boxes of goods to the pickpocket’s hideout.

One could say it’s quite an artful dodge, but it comes with its challenges. For starters, it often requires the hacker to have a higher level of access or specific database configurations to make those external requests. It’s also generally slower and less efficient than other SQL Injection methods, due to the roundabout way data is extracted.

Despite these hurdles, an Out-of-band SQL Injection attack can be especially sneaky, as it can bypass certain security measures and leave less trace in the database’s own logs.

To guard against this form of data theft, it’s crucial to have robust input validation, employ least privilege principles, and use secure configurations that limit the database’s ability to make external network requests. Additionally, monitoring network traffic for unusual external requests can help detect any attempted Out-of-band attacks.

In the world of SQL, it’s not just about guarding your ‘marketplace.’ It’s about knowing who’s coming, who’s going, and most importantly, where your data is being sent. With careful measures, you can ensure your data stays in-house and doesn’t end up in the wrong hands.


In our journey through the bustling marketplace of data, the secure fortress, and the meticulously planned party, we’ve explored the intriguing yet potentially dangerous world of SQL Injection. These cunning techniques – Union-Based, Time-Based Blind, and Out-of-band – remind us of the constant vigilance required to protect our valuable data. But fear not, for with understanding comes power. With robust validation, secure configurations, and a keen eye on our systems, we can ensure our ‘guest lists’ remain exclusive, our fortresses secure, and our marketplaces safe from any digital Artful Dodgers.

How to stay safe online:

  • Practice Strong Password Hygiene: Use a unique and complex password for each account. A password manager can help generate and store them. In addition, enable two-factor authentication (2FA) whenever available.
  • Invest in Your Safety: Buying the best antivirus for Windows 11 is key for your online security. A high-quality antivirus like Norton, McAfee, or Bitdefender will safeguard your PC from various online threats, including malware, ransomware, and spyware.
  • Be Wary of Phishing Attempts: Be cautious when receiving suspicious communications that ask for personal information. Legitimate businesses will never ask for sensitive details via email or text. Before clicking on any links, ensure the sender's authenticity.
  • Stay Informed. We cover a wide range of cybersecurity topics on our blog. And there are several credible sources offering threat reports and recommendations, such as NIST, CISA, FBI, ENISA, Symantec, Verizon, Cisco, Crowdstrike, and many more.

Happy surfing!

Frequently Asked Questions

Below are the most frequently asked questions.

What is the most common type of SQL Injection?

The most common type of SQL Injection is typically the classic or ‘Error-Based’ SQL Injection. This method exploits error messages returned by the database, enabling the attacker to retrieve information about the structure and contents of the database. However, the three types discussed in this article – Union-Based, Time-Based Blind, and Out-of-band – are also quite prevalent.

How can I protect my website or application from SQL Injection attacks?

Some of the most effective ways to protect your website or application from SQL Injection attacks include:

  • Input validation: Never trust user input blindly. Always validate and sanitize inputs to ensure they’re safe before using them in SQL queries.
  • Parameterized queries or Prepared Statements: These techniques ensure that user inputs can’t be interpreted as SQL code.
  • Least privilege principle: Limit the permissions of your database accounts. They should only have the minimum privileges necessary to perform their job.

Is SQL Injection still a threat today?

Yes, despite being a well-known vulnerability, SQL Injection remains a significant threat. This is mainly because of two reasons: many websites and applications still do not properly sanitize user input, and the SQL Injection techniques have become more sophisticated over time. As such, it’s crucial for developers to keep up-to-date with the latest security practices and to maintain a proactive approach to database security.

Author: Tibor Moes

Author: Tibor Moes

Founder & Chief Editor at SoftwareLab

Tibor is a Dutch engineer and entrepreneur. He has tested security software since 2014.

Over the years, he has tested most of the best antivirus software for Windows, Mac, Android, and iOS, as well as many VPN providers.

He uses Norton to protect his devices, CyberGhost for his privacy, and Dashlane for his passwords.

This website is hosted on a Digital Ocean server via Cloudways and is built with DIVI on WordPress.

You can find him on LinkedIn or contact him here.

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