SQL Injection Attack

A Complete Guide to SQL Injection Attack – Examples and Prevention Methods

Apart from sending phishing emails, intercepting the conversation between two entities, and hiding Trojans inside legitimate files, attackers may take advantage of poorly coded websites and apps and use them to execute their malicious activities.

One of the most common types of cyber threats based on coding vulnerabilities is a SQL injection attack, which allows hackers to access, alter, and delete information found in databases. SQLi can be fatal for companies that carry a significant number of their clients’ sensitive information, but the good news is that it can be handled easily.

The following post will provide a detailed image of the SQL attack, explain the way it works, and offer the strategies to help you mitigate the risks.

What is SQL Injection Attack?

SQL injection attack, also known as SQLi, is a code-based attack that’s used to exploit vulnerabilities in a website’s coding or an application’s software.

It allows hackers to access the existing data in databases, modify it, delete it, or make it unavailable. It can cause severe damage to companies that carry a lot of their clients’ data, but the truth is that it can be easily handled, unlike most other cyber threats.

How Does SQL Attack Work?

Most of the content generated on the websites we see today is handled through databases. Databases are a large piece of work, but thanks to programming languages, such as SQL, they can be managed more straightforwardly.

SQL stands for Structured Query Language, and it’s used for editing and querying information within different database management systems. It is based on several elements, which include:

  • Expressions: They may produce scalar values or tables, and they consist of rows and columns of data.
  • Queries: Queries are used to retrieve data based on the provided criteria.
  • Statements: Statements allow the data to be more accessible to control, and it includes program flow, transactions, connections, diagnostics, and sessions.
  • Clauses: They represent the components of different queries and statements.
  • Predicates: These are used to specify conditions necessary to limit the effects of queries and statements, or to change the entire application flow.

A hacker who wants to deploy the attack will look for vulnerabilities in the SQL structure and use them to inject a malicious code there. Before we provide an actual SQL injection attack example, we’ll explain how SQL statement functions:

sql injection attack example

As you can see, the statement consists of unique characters, which include:

  • Asterisk (*): It is an instruction for the SQL database to return all columns for the selected database row.
  • Equals (=): This is the instruction for the database to return only the values that match the searched string. In this case, it will show the user whose username is Andy and password 123456.
  • Single quote mark (‘): This is used to tell the SQL database where the search begins or ends.

The SQL injection is commonly performed through user input. Most web applications allow input via a form, which is the way of passing the information from front-end to back-end database for processing.

If a web app is poorly coded, it will allow the hacker to inject SQL of their choosing and grant them access to the database. That way, hackers can modify, delete, or copy the contents they find.

So, if the application does not sanitize the input, an attacker can easily insert a code and manipulate the entire process. For example:


The attacker’s input ‘admin’; — consists of two new, special characters:

  • A semicolon (;): It is used to tell the SQL parser that the current statement has ended.
  • A double hyphen (–): It shows the SQL parser that the rest of the line is a comment and that it shouldn’t be executed.

The action performed by using such code allows the attacker to log in with an administrator account, without having to specify the password.

Let’s see another SQL injection attack example:

Imagine that a hacker goes to a web app that’s used for buying and selling used computer equipment. Consequently, its database consists of confidential information about the people who have registered to a website, intending to buy or sell the equipment.

A typical SQL database of such a website may look like:

what is sql injection

For example, when a user types “gaming keyboard” in the search box, the URL they may expect to see is www.exampleofastore.com/keyboards/gaming-keyboards/itemid=29.

The ending of a URL, itemid=29, indicates that the number of a particular gaming keyboard is 29 and that the link provides the name and description for such an item.

When such information is visible in the URL, a hacker may see an opportunity to make some changes, such as www.exampleofastore.com/keyboards/gaming-keyboards/itemid=29 or 1=1.

Therefore, the modifications in the SQL query will look like this:

how to prevent sql injection

The statement that says that 1 equals 1 is always true, which means that the query will return all of the product names and descriptions in the database, even those that are not supposed to be accessed.

This action is possible because hackers often take advantage of incorrectly filtered characters, such as using a semicolon to separate two fields. That way, they can make significant changes to a website database, including deleting the entire category.

Still, the major inconvenience SQLi can bring is granting the hackers access to a database. By injecting the code UNION SELECT user-name, password FROM USERS, hackers will make a request that will pull names and passwords of every user that exists in a database.

This is just one of the examples that describe the way a hacker can manipulate the code that’s written incorrectly. Make sure your IT team is consistently checking on a code structure and correcting errors that could open the door to vulnerabilities and exposure.

What are the Types of SQL Injection Attacks?

SQL injection attacks are usually divided into three categories:

  • In-band SQLi (Classic)
  • Inferential SQLi (Blind)
  • Out-of-band SQLi

In-Band SQLi (Classic)

In-band SQLi is also known as the classic one, which implies its simplicity and efficiency. It’s based on the attacker’s attempt to use the same channel of communication to launch their attacks and gather the necessary information.

There are two types of such an attack:

  • Error-based SQLi: This is a technique where attackers rely on error messages shown by the database server, trying to obtain information about the structure of the database. Despite the efficiency of such messages during the phase of development of a web app, they shouldn’t be able on a live site but be logged to a file with restricted access.
  • Union-based SQLi: It takes advantage of the SQL UNION operator, which is used to combine the results of two or more SELECT statements. The attacker combines these results into a single one, making sure it returns as a part of the HTTP response.

Inferential SQLi (Blind)

An attacker will perform Inferential or Blind SQLi by sending data payloads to the server, intending to learn more about its structure. It’s called a blind SQL injection attack because the data is not transferred from a website’s database to the attacker, which prevents them from seeing information about the attack in-band.

Such attacks may be slower to execute, but they are as harmful as those whose execution occurs immediately.

There are two subcategories of Blind SQLi:

  • Boolean: It’s an attack where a hacker sends a SQL query to the database expecting the application to return the result. The result will depend on whether the query is true or false. The result will determine whether the information within the HTTP response will modify or stay unchanged.
  • Time-based SQLi: This method is performed by a hacker who sends a SQL query to the database, which requires it to wait a couple of seconds before it can react. Hacker can determine whether the query is true or false based on the time it takes a database to respond.

Out-of-band SQLi

Out-of-band SQLi is a form of code-based attack that can be deployed only when certain features are enabled on the database server that a web app uses.

Attackers find it convenient when they can’t use the same channel to launch the attack and get valuable information or when the server is unstable or unresponsive, making it impossible for actions to be performed.

How to Prevent SQL Injection?

There are numerous ways of SQL injection prevention, and you need to make sure you follow them in order to protect your data from malicious activities executed by hackers.

Have a look at the following tips that will help you prevent SQL injection:

1.      Sanitize

The first step you should complete is so-called “sanitization,” which means that you need to write the code that can detect illegitimate user inputs. We have already seen the example where the attacker takes advantage of poorly handled login options; therefore, you shouldn’t risk.

It’s essential to limit user input, which means that you should focus on filtering the content. For example, make sure the field that requires email address allows only the characters found in a legitimate email address, while fields that require a phone number should be filtered to allow only the digits allowed in the phone number, etc.

2.      Avoid Using a Dynamic SQL

Although sanitization may be the first thing you should do, it’s vital to know that it won’t guarantee a 100% security. Consequently, you’re advised to use prepared statements, parameterized queries, or stored procedure when it’s possible.

However, you should be aware of the fact that such procedures may prevent some SQL injections while opening the door to other vulnerabilities at the same time.

3.      Provide Consistent Updates and Patch Management

Vulnerabilities in a web app usually come as a result of irregular updates and the lack of adequate patches. These factors are critical because it may be challenging to spot vulnerabilities hackers can exploit using SQLi, which is why you need to ensure that your database is regularly updated and patched.

4.      Implement a Web Application Firewall (WAF)

Web Application Firewall (WAF) can help you filter out any malicious data and provide some necessary security protection against a new vulnerability before a patch is available.

There are different WAF modules you can download, and they are often created for Apache, Microsoft IIS, Nginx web servers, and more. They can protect you from the most advanced SQL injection types and catch their attempts to sneak SQL through web channels.

5.      Utilize Appropriate Privileges

It’s recommended not to connect to your database using an account with admin-level privileges unless you have no other choice. Namely, it’s much safer to use a limited access account and limit a hacker’s opportunity to execute their malicious intentions.

6.      Encrypt, Encrypt, Encrypt

By assuming that your web app is not safe and encrypting or hashing usernames, passwords, and other confidential data and connection strings, you make sure the privacy is brought to the next level.

7.      Don’t Reveal Too Much Information

As you could see, hackers can learn a lot about your database from error messages. Accordingly, it’s vital not to give them enough information that could help them execute their plans.

Make sure error messages display only on the local machine, while external hackers get only the notification that their actions resulted in an error that can’t be handled.

Bottom Line: How to Stay Protected from Code Injections?

You should know that hackers can exploit even the simplest error in your code, which is why you need to revise it from time to time and detect all the potential vulnerabilities that may exist in your app.

SQL injection attacks can be easily executed without you even noticing that someone’s been manipulating your coding. Therefore, download and install the apps that will inspect your code and detect and fix any potential problems. Besides, make sure you follow the tips on how to prevent SQL injection attack we’ve provided to ensure your database privacy.

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