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What SQL Injection Is & How It Works

An image displaying a close-up of a web input for a login and password

SQL injection is a mechanism that cyber attackers use to interfere with application queries to a database. Specifically, SQL injection exploits a security vulnerability and gives hackers access to data that they shouldn’t have access to.

An illustration of how SQL injection attack works

How SQL Injection Works

To understand SQL injection (SQLi), you have to first understand code injection and SQL.

“Code injection” is an umbrella term for any attack that “injects” code into a program’s existing code. At that point, the code gets interpreted and executed by the application, often without being noticed by the user. 

These attacks are different from Command Injection attacks. A command injection manipulates code that already exists, but code injection inserts new code into the application.

SQL stands for Structured Query Language. It is a programming language that is used to interact with data in a relational database. Relational databases use tables to organize information into rows and columns. The information is presented in a way that shows the different relationships that exist between data values.

When you make a request to a relational database, the code uses SQL to retrieve the information and present it to you. 

SQL injection is one specific type of code injection that inserts malicious code into the SQL requests. These attacks are popular because they are inexpensive – no special equipment is required. Additionally, they are a relatively easy attack to launch. 

Unfortunately, the aftermath of an SQLi can be brutal on the attack’s victims. 

What is the goal of an SQL injection?

Hackers use SQLi to access data they shouldn’t be able to access. They can use this information to wreak havoc on your operations and security. 

Here are some examples of what these hackers can do when they break into your database:

  • Compromise your privacy and the privacy of your users (credit card numbers, phone numbers, social security numbers, and anything else that your users store on your database)
  • Expose your company’s sensitive data 
  • Take over your system using maliciously-obtained administrative privileges
  • Gain general access to your whole system, including user credentials
  • Damage your data integrity (deleting information from your system, adding information, manipulating data, etc)

Because many companies don’t actively monitor their databases – and sometimes fail to properly secure them – these SQLi attacks are not always noticed right away, giving the attacker time to cause significant amounts of damage. 

Regrettably, these attacks can be incredibly expensive to repair. Stolen banking information can lead to a direct loss of income, and sensitive company information getting to the public can cause all sorts of problems. 

Additionally, if your user data is compromised, you may end up losing customers or even facing lawsuits. 

Examples of SQL Injection Attacks

SQLi can be used to execute a number of different attacks. 

These include: 

  • Retrieving the database’s hidden data
  • Damaging the application’s logic, so that the queries return inaccurate or unusable information
  • UNION attacks, which allows the hacker to retrieve data from more than one database table at once
  • Extracting information from the database 
  • Blind SQLi, which prevents the correct query results from returning in the application’s responses

SQL injections are frustrating for the average small or mid-size business owner because they are easy for hackers to use, but difficult for people without computer programming backgrounds to anticipate, deflect, or respond to. 

Detecting SQL Injection Vulnerabilities

Most of the time, SQLi vulnerabilities are easy to identify and relatively easy to fix, before an attack can ever occur. 

To do a manual detection, you will simply use a systematic testing process against each of the application’s entry points. If you have experience with SQL coding, this should all be pretty easy. 

Do this by taking any of the following steps: 

  • Submit the single quotation mark character ( ‘ ) and look for errors and anomalies. 
  • Submit some SQL syntax to evaluate the original value of each entry point, looking for differences in the application’s responses.
  • Use Boolean search conditions (OR 1=1 and OR 1=2) to identify differences in the responses from the application. 
  • Submit payloads that, when executed within an SQL query, trigger a time delay. Are there any differences in the time it takes to respond? 
  • Submit an OAST payload that causes an out-of-band network interaction when it is executed by an SQL query. Then, monitor for the interactions that follow.
SQL source code

What If Your Company Has Been the Target of an SQLi Attack?

Responding to an SQLi attack is best left in the hands of your company’s programmers. If you do not have dedicated programmers, you can reach out to a database security company for assistance. 

Preventing SQLi Attacks

To prevent an SQLi attack, you need to utilize input validation and parameterized queries with prepared statements. 

Don’t input application code directly. Instead, sanitize all SQL input, including web forms, logins, and more. 

If you encounter a malicious code element, such as that single quote character, remove it immediately. 

You can also make it so that your database errors on your production sites are not visible. Those errors give attackers information that they can use to build their SQLi attack and gain information about your databases. 

Additional advice

  1. Keep your software updated
  2. When a security patch is available from a vendor, run it
  3. Utilize allowlist input validation – that way, unvalidated user input will not be able to be added to the query
  4. Accounts that have database access should have minimum security privileges to prevent abuse of those accounts
  5. To prevent confusion between the malicious input and the SQL code, escape the user-supplied input before it is entered into a query
  6. Limit sharing of database accounts across more than one website or application
  7. Validate user-supplied input

Don’t Forget to Secure Your Database

If there is one thing that the average small or mid-sized business owner can do to prevent SQL injections, it is to remember the importance of database security. 

Maintaining excellent database security standards will protect your business from SQL attacks and so much more. 

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