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What Is SQL Injection & How To Prevent It?

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4th Oct, 2023
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What Is SQL Injection & How To Prevent It?

With the rapid evolution of technology, the world is seeing a subsequent shift to online for everything. The Internet is the one-stop solution for everything from storing relevant documents to conducting financial transactions. However, this also means increased threats to cyberspace through hacking, identity theft, etc. Web hacking generally targets the areas that can destroy your important applications. SQL injection is a common approach to harming data-driven applications.

SQL injection attacks are generally performed through any application input or web page. Attackers search for vulnerabilities and loopholes in a web page or application to execute malicious commands. This blog will comprehensively answer ‘What is SQL injection and how to prevent it’. 

What Is SQL Injection?

SQL injection is a web security attack and vulnerability performed by executing malicious codes. The attacker gains access to the application of a database and damages sensitive data by either making changes to it or stealing it. Injection attackers incorporate SQL queries to change, modify, update, or delete sensitive information from the database.

Recent years have seen an alarming increase in SQL injection attacks and security breaches.  These attacks may also affect the server or back-end infrastructure, sometimes escalating to DDoS attacks. 

The Intention Behind an SQL Injection

The most prevalent question when discussing SQL injection is, ‘What is the purpose of an SQL injection?’ The main motive of SQL injection attackers is to access sensitive information in a database. 

The purpose of an SQL injection is to exploit vulnerabilities in a software application’s security by manipulating the input fields or parameters that interact with a database using Structured Query Language (SQL). This process aims to damage sensitive data such as updating, modifying, deleting, or stealing it with malicious intentions. This exploitation can have various malicious intentions, and it seriously threatens the confidentiality, integrity, and availability of data within a database. 

SQL Injection Types

SQL injection is a widespread cybersecurity threat that comes in various forms, each with its own methods and goals. Depending on their potential to damage sensitive data, it can be classified into three broad categories as described below:

1. In-band SQL Injection

In this type of SQL injection, the attacker launches malicious commands on the same communication channel used for deriving information. It is one of the most effective and straightforward SQL injection attacks, thus making it one of the most used. 

In-band SQL injection can be divided into the following sub-categories:

  • Error-based SQL injection: This is the type of SQL injection where an attacker attacks in a way that produces error messages in the database. People with the affected database will see the error messages, and the attacker will gain access to sensitive information about the features and structure of the database.
  • Union-based SQL injection: Attackers use the UNION SQL operator to combine their malicious query with a legitimate one in the application’s database. This can allow them to extract data from other tables or manipulate the query’s result. 

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2. Inferential (Blind) SQL Injection

In Inferential SQL injection, the attacker does not mess with the immediate web page but proceeds in a way that sends data payloads to the main server. This process is also known as blind SQL injection. Attackers use this technique when they can’t view the application’s responses directly. They infer the data’s existence or values by observing how the application responds to their queries over time.

Blind SQL injections are difficult and slower to execute but can be dangerous as they identify the behavioural patterns of the server.

Inferential SQL injection can also be divided into two sub-categories, as illustrated below:

  • Boolean-based SQL injection: Here, the attacker writes an SQL command as a query and sends it to the database, asking the application to return a response. The response depends upon the query being true or false. The HTTP results of the query may portray some changes or can remain the same. The attacker then analyses whether the message is true or false. 
  • Time-based SQL injection: The attacker initiates a SQL query to the database, prompting the system to wait briefly before responding, usually for a few seconds. The time period of the response from the database allows the attacker to evaluate the legitimacy of the query in terms of true or false. Based on the query results, an HTTP result will be generated immediately or after some time. The attacker can then evaluate whether the status of the message is true or false even without accessing the information of the database.

3. Out-of-bound SQL injection

Out-of-bound SQL injection cannot be performed when certain database features are missing. This is an infamous type of SQL injection that depends upon the functionalities of a database server. The attacker cannot launch this attack if certain functionalities are not enabled. While configuring, it may look like a database administrator issue.

This injection attack is used when the attacker cannot use the same communication channel to launch an attack as in the case of in-band SQL injection. The attacker can carry out this attack even if the database server is unstable and slow. This method is based on the ability of the server to forward HTTP or DNS requests to pass on sensitive data to the attacker.

Executing a SQL Injection Attack

To know ‘what is SQL injection attack‘ is, one must also understand how an SQL injection attack is conducted. To launch an SQL injection attack, the attacker locates the vulnerable user inputs in a web application or page. The attacker creates harmful input content through malicious payloads and sends it as user input, followed by executing malicious SQL commands in the database containing important data.

SQL is a programming language that writes queries and commands to manage the data stored in relational databases. It is generally used to update, modify, access, or delete data. Organisations largely store their sensitive data in SQL databases. SQL commands are sometimes applied to execute the operating system’s commands. Therefore, a successful SQL injection attack may result in very serious outcomes.

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What Are Some Examples of SQL Injection?

Here are some of the most common examples of SQL injection attacks that will help you better understand the concept along with the commands:

Example 1:

The first example depicts how an attacker uses SQL commands to gain access to a database and act as an administrator. The attacker writes commands on a web server to authenticate with a username and password.  

In the following example, the table name is ‘users’, and the requested column names are ‘username’ and ‘password’.

# Define POST variables
uname = request.POST[‘username’]
passwd = request.POST[‘password’]

# SQL query vulnerable to SQLi
sql = “SELECT id FROM users WHERE username = ”’ + uname + “’ AND password=”’ +
passwd + “”’

# Execute the SQL statement 
database.execute(sql)

These SQL commands are vulnerable inputs, and the attacker can easily alter or modify any user input. For instance, the attacker can alter the password field and set it to:

password' OR 1=1

Therefore, in this case, the database will execute the following SQL command:

SELECT id FROM users WHERE username='username' AND password='password' OR 1=1'

 

Because of the command mentioned above, the ‘where’ clause will return the result of the first ID, and the value of the username and password is immaterial. In this way, an attacker gains unauthorised access to the database and also gets the privileges of an administrator. The attacker can further manipulate the database by executing the following query:

MySQL, MSSQL, Oracle, PostgreSQL, SQLite
‘ OR ‘1’=’1’ --
‘ OR ‘1’=’1’ /*
– MySQL
‘ OR ‘1’=’1’ #
– Access (using null characters)
‘ OR ‘1’=’1’ %00

‘ OR ‘1’=’1’ %16

Example 2: Union-based SQL injection example

The union operator is the main feature of launching an SQL injection attack here. In this type of attack, the attackers can combine the outcomes of two select statements to return a single result. 

Like a legitimate user, the attacker sends an HTTP request to a vulnerable web page. The payload sent by the attacker can alter and modify the query using the union operator that is generally attached to the malicious SQL command. The result of the chosen statement will show the outcome of the original query combined with that of the malicious query. 

The following SQL commands show the example of union-based SQL injection:

GET http://testphp.vulnweb.com/artists.php?artist=1 HTTP/1.1
Host: testphp.vulnweb.com

 

GET http://testphp.vulnweb.com/artists.php?artist=-1 UNION SELECT 1,2,3 HTTP/1.1
Host: testphp.vulnweb.com

 

GET http://testphp.vulnweb.com/artists.php?artist=-1 UNION SELECT 1,pass,cc FROM
users WHERE uname=’test’ HTTP/1.1
Host: testphp.vulnweb.com

 

SQL Injection Attack: Preventive Measures

Now that we have covered the what and how of SQL injection attacks, the next question is, ‘What are the solutions for injection attacks?’ Preventing injection attacks is not easy. Implement the following preventive techniques to protect your data from SQL injection attacks:

  • Implement parameterised queries and prepared statements: You may use parameterised queries, which help analyse and treat the SQL statements securely. Only those SQL commands parameterised with safety features will be executed in this case. It allows the database to record only prepared statements and eliminate fake commands.
  • Object-oriented mapping: This is a great way of securing your data from SQL injection attacks. Companies nowadays use object-oriented relational mapping frameworks over traditional mapping tools. Object-oriented mapping offers seamless conversion of SQL results into codes. It helps developers keep the data safe against SQL mapping. To answer ‘what is SQLmap used for’, it tests the vulnerabilities in web applications and web pages so the attacker can easily access the database. 
  • Escaping inputs: This is a new way of protecting your data from SQL injection attacks, where many programming languages have some standard functions for data protection. One should be alert while applying escape characters in the SQL statements and commands.

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Conclusion

Web hacking using SQL injection can take advantage of a company’s database and damage it. These attacks can manipulate the database server in charge of the company’s web applications. Any company that uses an SQL database is vulnerable to SQL injection attacks. These attacks can cause irreversible damage to databases and servers, resulting in far-reaching losses in terms of finance and reputation. 

Understanding these attacks is crucial for developers and security professionals to protect applications and databases from such vulnerabilities. Proper input validation, parameterised queries, and regular security assessments are essential in preventing SQL injection attacks. Enrol in an online cybersecurity course to gain in-depth knowledge on ‘what is SQL injection in cybersecurity’ and the various kinds of SQL injection. 

Profile

Pavan Vadapalli

Blog Author
Director of Engineering @ upGrad. Motivated to leverage technology to solve problems. Seasoned leader for startups and fast moving orgs. Working on solving problems of scale and long term technology strategy.
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Frequently Asked Questions (FAQs)

1What are some real-life examples of SQL injection?

Some real-life examples of SQL injection attacks would be when attackers successfully gain unauthorised access to your credentials, such as username and password. In this way, the attacker exploits the vulnerabilities in a company's database using your name. Another instance is when the attacker monitors your activities by successfully installing a bug in your system.

2Which SQL injection is most used?

The union-based SQL injection is the most popular type of injection attack. The union operator is the key in this attack, displaying the results by combining two select statements.

3What are the solutions for injection attacks?

You can protect your system against injection attacks by incorporating parameterised queries, using prepared statements, installing detection and protection software, input validation, etc.

4Is SQL injection active or passive?

SQL injection can be categorised into both active and passive forms. SQL injection is said to be passive when considering the database's data exposure. If the database's data has been altered or modified, it is an active form of SQL injection.

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