Guide | An Overview to SQL Injection

What is SQL injection?

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SQL injection is a programming attack that forces a database to give out data by inputting malicious code. It can be done by taking advantage of the lack of input sanitizing or by not fixing mistakes in the code. 

SQL injection is often hidden in text fields, like comment boxes or blogs, and it can happen when you enter your username and password on a website. 

This type of attack usually happens when the programmer hasn’t written good enough security code to make sure the connection between the browser and database is safe.

SQL injection

It is a type of attack where the hacker injects SQL commands through vulnerable Web Applications or functions. 

It is called an injection because it happens when the hacker inserts the rogue SQL commands into the application’s input parameters, thereby exploiting the data-handling capabilities of the SQL database. 

The goal of this type of hacking is to gain unauthorized access to data and either modify it or steal it.

SQL injection attacks are caused when a website accepts unescaped input from a user. This could be an email address, a name field, or any other input parameter. 

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The computer program will then search for the query string in its database and execute it. For example, if the user types in “Joe’ OR 1=1;–” and this gets accepted by the program, then there is a huge risk for SQL injection.

In this article, we will go over step by step guide on SQL injection and gain knowledge on how to avoid potential attacks from hackers.Also study the Interview Question For SQL.

What is SQL injection?

SQL injection attack

SQL injection is a type of code injection technique that exploits SQL databases. It works by inserting SQL commands into strings that are later passed to an instance of the Structured Query Language (SQL). 

The most common types of SQL injections are: – 

  1. Union-based queries: which allow the attacker to retrieve more data than what was specified in the query.
  2.  Error-based queries: which return an error message instead of data. 
  3. Type confusion: which causes SQL to view a column as a different type from what it is.

SQL injection is typically used when an application uses dynamic SQL—queries that are generated dynamically by the database. Dynamic SQL queries often use user input as part of their query.

For example, adding an integer to the end of a character string will cause SQL to dynamically produce a WHERE clause that includes the string value in the WHERE condition. 

SQL injection is often used to access data from databases without permission. This can be done by exploiting an application’s error handling function, which allows SQL queries to execute when specific errors occur. 

For example, if a web application uses dynamic SQL queries where input is validated using JavaScript validation functions, an attacker may be able to inject SQL commands that have been pre-built into JavaScript functions. 

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An SQL injection happens when the input for a query is sent when the server was expecting a standard text string, but instead got some input that is processed as SQL queries.

How does SQL Injection work?

SQL injection is a method of attack against web applications where the attacker tries to exploit weaknesses in the database access layer (DAL) of an application by injecting special characters into SQL queries sent through the URL parameters. 

If successful, these injections allow arbitrary commands execution under the privileges of the user making the query, allowing the intruder to steal data, delete records, add new ones, change configuration settings, etc. Here we will explain how it works. 

  • The first step in SQL injection is to find an input field on a web form or application (e.g. “username”) and enter a string that will be interpreted as part of an SQL query.
  • The second step is to add a semicolon (;) followed by the malicious command, which will then be executed by the database management system. 

The following string, which uses a semicolon to terminate the SQL query, will return all available records from the database. The command will also be executed by the database management system: SELECT * FROM users; Unsafe: select from users.

  • The third step is to add a backslash (\) followed by the malicious command, which will then be executed by the database management system. 

Again, this will return all available records from the database. The command will also be executed by the database management system: 

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SELECT FROM \users; 

Unsafe: select from users;

Finally, we add a space followed by the malicious code, which will be executed:

SELECT FROM \users; 

/* Unsafe: select from users;

  •  The fourth step is to add a backslash followed by the output of the command. 

This will create the SQL injection attack:

SELECT c.*, l.length FROM customer c LEFT JOIN length_list l ON (c .id = l.cust_id)SELECT c. ,

 l.length FROM customer c LEFT JOIN length list l ON ( = l.cust_id)SELECT “1\0” — SQL injection attack

 length — 1    

FROM customer c    

LEFT JOIN length list l ON (c .id = l.cust id)SELECT c.

 l.length FROM customer c LEFT JOIN length list l ON (c .id = l.cust id) where 1 is the length of the column, and “1” is the SQL injection attack that eventually will run through your database, causing problems for you and your website.

Types of SQL Injection Attacks

Types of SQL Injection Attacks

SQL injection attacks are a type of code injection technique, used to attack data-driven applications, in which malicious SQL statements are inserted into an entry field for execution (e.g. to dump the database contents to the attacker).

The two most common types of SQL injection attacks are:

1) Error-based SQL injection attack:

Error-based SQL injection attack is what we will be discussing in this section. Error-based SQL injections happen when an application fails to validate input from the user before passing it to a database query. 

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The attacker’s goal is then to exploit this lack of validation by providing crafted input that forces the application into executing unintended commands against the database server. 

The attacker’s goal is then to exploit this lack of validation by providing crafted input that forces the application into executing unintended commands against the database server.

Let’s start with a very simple example of an error-based SQL injection vulnerability in order to help illustrate this concept. 

Take the following URL:

The following is an error-based SQL injection vulnerability: vulnerability. Php?id=123

The attacker’s goal is to provide a string that forces the application into executing unintended commands by exploiting the lack of validation. 

The following would be a good payload:

+– Inject payload here –+ –+ CREATE TABLE t1 (a VARCHAR(255) PRIMARY KEY, b, c VARCHAR(20));

+– Inject payload here –+An example error message would be:

Error 404 on file ‘vulnerabilities.php’: SQL Error: Table ‘./myfiles/commoncat.table1’ doesn’t exist – create table t1 (a VARCHAR(255) PRIMARY KEY.

2) Inference-based SQL injection attack:

Inference-based SQL injection attack is a type of attack that exploits the inference process in order to get the database to reveal information that it should not reveal.

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Information is revealed through inference. When a database assumes that data is not present or does not exist. Thus saving processing time and resources on the part of the database. 

This means that information can be extracted by asking questions of the database that it would normally be able to answer with only a binary answer (i.e., yes or no). By crafting SQL injection queries, an attacker can ask the database to perform inferences that they should not be able to do.

3) Blind and Non-Blind Attacks: 

The blind attack does not require knowledge of the database structure and cannot be defended against easily. However, if the attacker has knowledge of the database structure. They can exploit it with a non-blind attack. Which in return, can be defended against more easily because they know what they’re attacking.

Prevention of SQL Injection 

Prevention of SQL Injection 

SQL injection attacks are most successful when they are used against poorly written web applications. 

A few of the most common causes of SQL injection vulnerabilities are: 

  • Using dynamic SQL, which is not sanitized before being executed.
  • Using string concatenation to build parameterized queries and then not validating input.
  • Allowing users to submit data that is not filtered or properly validated before being inserted into a query. 

A SQL injection attack uses the underlying data engine’s ability to embed dynamic SQL queries in place of input fields. This allows unusually long and complex queries to be constructed by manipulating user-supplied data. 

The input is then sent, typically as POST or GET request variables. When the value of these variables is executed using dynamic SQL. They typically produce unexpected results, such as altering the database structure.

SQL injection can be used to accomplish a variety of attacks. Such as changing the data in a database or causing denial-of-service. This is done by consuming all of the available memory on one or more web servers.

SQL injections are a type of attack in which a hacker inserts SQL commands into an entry box. This causes SQL code to run. 

The attacker can either insert a line of text. They can find out the name of the related web program, such as webmail. They also look through the source code for vulnerabilities. 

The best way to prevent it is by using input fields that filter out these characters and encoding data on the server-side before sending it back to the browser.

It is possible to input SQL commands in an entry box. But these would not execute on the server as an attacker would need to find out the name of the related web program, such as webmail, and look through the source code for vulnerabilities.

In A Nutshell…

SQL injection attacks are a result of the misuse of SQL. This is a declarative language for managing data in a relational database management system (RDBMS). 

The SQL language provides a way to specify the query or data manipulation that should be performed on a database. It is often used in conjunction with procedural languages such as C, C++, or Java.

We now know that it is a malicious attack that exploits the security vulnerability in Structured Query Language (SQL) databases

This vulnerability happens when user input is taken and then executed as part of an SQL command, which is not looked at by the developer. Find out more about SQL injection and how to protect against it on this blog. Visit codersera for more information.


  1. What is SQL injection vulnerability?

    SQL injection is a web security vulnerability that allows an attacker to interfere with the queries that an application makes to its database. It generally allows an attacker to view data that they are not normally able to retrieve.

  2. What causes SQL injection vulnerabilities?

    To make an SQL Injection attack, an attacker must first find vulnerable user inputs within the web page or web application. A web page or web application that has an SQL Injection vulnerability uses such user input directly in an SQL query. The attacker can create input content.

  3. What is a SQL injection attack for example?

    SQL injection, also known as SQLI, is a common attack vector that uses malicious SQL code for backend database manipulation to access information that was not intended to be displayed. This information may include any number of items, including sensitive company data, user lists, or private customer details.

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