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What is SQL Injection? Definition, How It Works, Prevention Tips & More

by Chris Brook on Thursday December 8, 2022

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Learn what a SQL injection is, how attackers can use them to damage organizations and their data, and how to best protect against SQL injection attacks in this blog.

SQL injection is a type of security vulnerability that enables cyber attackers to intercept and interfere with queries from an application to a database. It can result in serious consequences, such as identity spoofing, altering data, and exposing sensitive data. In this article, we’ll discuss SQL injection in more detail and best practices for preventing SQL injections. 

What is SQL Injection? 

SQL injection (SQLi) is a security vulnerability that can result in a cyber attack. An attacker can use malicious SQL code to manipulate the database of an application and access sensitive information. It can also allow the attacker to modify or delete data in the database, making the application behave abnormally.

An SQL injection can be used to affect the underlying server and to perform a Denial of Service (DoS) attack. It can also execute administrative operations on the victim database and even issue malicious commands to the operating system.

Are SQL Injections Still Relevant?

Even though SQL injections have been around for decades, they are still relevant and dangerous. For example, a recent SQLi vulnerability was discovered in the e-learning platform Moodle.

There have also been several high-profile SQLi-based data breaches that have led to financial damage and tarnished the company’s reputation. For example, a group of hackers called RedHack attacked the Turkish government website using SQL injection.

In another example, hackers used SQL injection to hack into the systems of 7-Eleven and several other companies.

SQLi Operation

An SQLi attack works by injecting an SQL query into the application. With an SQL injection, the attacker can access unauthorized data, spoof identity, modify/delete records, shut down the database, or become the database administrator without being noticed.

Since PHP/ASP applications have older functional interfaces, they are more susceptible to SQL injections. On the other hand, ASP.NET and J2EE applications have lower chances of being exploited by an SQL injection attack.

SQL injections have a high impact and their severity depends on the imagination and skill of the attacker. In-depth defense measures can lower the severity to some extent, but in many cases, SQL injections can have a big impact on businesses.

What Can a Successful SQL Injection Do?

With a successful SQL injection, an attacker can gain access to sensitive data that includes personal information, passwords, credit card numbers, etc. The attacker can also get a backdoor entry into the organization and cause long-term damage without being noticed.

What is a Blind SQL Injection?

A blind SQL injection is when an attacker asks the database a true/false question and checks the answer to determine if a vulnerability exists. This means that retrieving data from the database might require the hacker to take some extra steps, so while it’s a little more difficult, the hacker can still gain access. The risk factors from blind SQL injections are the same as those from normal SQL injections.

How to Prevent SQL Injections

SQL injections happen when attackers enter data with SQL syntax into the web form of the application. An organization can prevent SQL injections by performing input validation and having parameterized queries. Another option is to ensure that input from users isn’t used directly by the application code. This requires input from login forms to be sanitized before it reaches the application, with all possible malicious elements being removed in the process.

Database errors are often used by attackers to determine if the system is vulnerable to SQL injections. As such, database errors should not be visible, making it harder for any possible vulnerabilities to be found. 

Even if a company discovers a vulnerability, it might not always be possible to immediately fix it. For example, if the vulnerability is in open source code, it cannot be avoided. In such a case, a firewall can be used to make sure the input is clean.

Preventing SQLi vulnerabilities isn’t always easy. Different steps can be taken, depending on the type of SQL vulnerability. However, there are some general steps an organization can take to keep its applications safe.

Create Awareness

Everyone developing and testing the web application should be aware of SQL injections and the risks associated with them. Proper security training should be given to developers, DevOps, and QA staff.

Don’t Trust User Input

All user input through web forms or other sources should always be treated as untrusted. Since any input can be used to insert an SQL injection into the system, it should be sanitized before it reaches the application. Even if the input is from internal users, it still has the potential to harm the application and should be verified before it reaches the database.

Don’t Use Blacklists

Organizations generally use blacklists to verify the input, but a seasoned attacker can circumvent the blacklist by hiding the malicious code. It’s therefore best to filter the input by using a whitelist and to only allow the verified data to enter the system.

Use New Technology

Older web technologies don’t have adequate protection against SQL injections. If a company is working on old technology, it’s advisable to upgrade and use the latest version in their development environments.

Scan Applications for Vulnerabilities

SQL injection vulnerabilities could be due to coding flaws or because of external modules or libraries. To stay safe, organizations should regularly scan their web applications to ensure there are no vulnerabilities. If a vulnerability is detected, it should be fixed as soon as possible, before it can be exploited by attackers.

An SQLi attack can result in huge losses, both financially and to a company’s reputation, and keeping your applications safe from this vulnerability should always be high on your company’s IT priority list. You can keep your applications secure and safeguard your sensitive data against SQL injections by following best practices such as

  • scanning apps for vulnerabilities, 
  • utilizing new technology, 
  • creating awareness, and
  • not trusting user input.

Tags:  Vulnerabilities

Chris Brook

Chris Brook

Chris Brook is the editor of Digital Guardian’s Data Insider blog. He is a cybersecurity writer with nearly 15 years of experience reporting and writing about information security, attending infosec conferences like Black Hat and RSA, and interviewing hackers and security researchers. Prior to joining Digital Guardian–acquired by Fortra in 2021–he helped launch Threatpost, an independent news site that was a leading source of information about IT and business security for hundreds of thousands of professionals worldwide.

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