What is SQL Injection? Types, Impact, and Prevention

Quick Summary: Cyber threats range in their attack methods and impacts. SQL injection is a kind of cyber threat that arises due to vulnerabilities in application code and poses risks of data theft. In this post, we’ll break down what SQL injection is, how it works, and the most effective ways to prevent it.

SQL Injection (SQLi) remains one of the most critical web vulnerabilities, making a place in the OWASP Top 10 vulnerability list for years. It occurs when attackers inject malicious SQL commands into an application’s query logic, forcing the database to execute unintended actions.

The consequences are real. In the Freepik data breach, attackers exploited an SQL injection flaw to expose over 8.3 million email addresses and 3.7 million hashed passwords - a single weak query turned into a massive data leak.

SQL injection attacks don’t just read data; they can alter, delete, or take full control of your application’s database. Organizations have lost millions to incidents that started with just a few lines of unvalidated input.

In this article, we’ll explain how SQL injection works, why it’s still so effective, and what developers and security teams can do to eliminate it from their stack.

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What is SQL Injection?

SQL Injection (SQLi) is a web application vulnerability that allows attackers to manipulate database queries and gain unauthorized access to data. It happens when an application directly uses user input to build SQL statements without properly validating or sanitizing it.

In simple terms, attackers insert malicious SQL commands into input fields (like login forms or search boxes). When the backend executes these commands, they can bypass authentication, read or alter data, or even delete entire tables.

The impact of simple SQL injection on a business is huge. A successful attack may cause unauthorized viewing of user lists, modification or deletion of tables, and gain administrative rights to the database.

In fact, when we calculate the potential cost of an SQLi, it’s essential to consider the loss of customer personal data, such as phone numbers, addresses, and credit card details.

When talking about SQL (Structured Query Language), it is the programming language used to manage and interact with relational databases. It stores, retrieves, updates, and deletes records. Because nearly every modern application relies on SQL databases, a single unvalidated query can expose critical information or disrupt entire systems.

SQL Injection has consistently ranked among the OWASP Top 10 vulnerabilities, not because it’s new, but because it still works on poorly validated code written every day.

SQL Injection Attack: How Does It Work?

An attacker exploits SQL injection vulnerability to get administrative access bypassing the security. Mostly vulnerability comes from unexpected data types entered into the username and/or password fields such as commands. Let’s see a few SQL injection examples below to understand how the attack occurs.

The following is a pseudo script that is executed on a web server. The script is used to authenticate users with a username and a password. The database consists of a table named users that further contains “username” and “password” columns.

user_name = request.POST[‘username’]  user_password = request.POST[‘password’]  #code to query username and password  user_sql = “SELECT id FROM users WHERE username=’” + user_name + “’ AND password=’” + user_password + “’”  #statement to execute the SQL query  database.execute(user_sql)

An attacker can exploit the input fields with tricky SQL queries. The SQL statement is vulnerable, and an attacker can enter SQL commands in the input fields that will modify the statement that the database server is supposed to execute.

The attackers can use the following tricks to alter the statements and get unauthorized access to the database.

• Use of single quote and password to:

password’ or 1=1

After this, the following SQL query is run:

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

The "or 1=1” causes the server to return the first id from the Users table irrespective of the username and password. Since mostly the first id belongs to the administrator, the attacker eventually gets administrator access bypassing authentication. After this, the attacker can take control of the execution of the SQL query and launch malicious actions.

• Use of “=” trick

For example, a hacker enters “OR” “=” into the username and password fields. As a result, the resulted SQL query will look like the following:

SELECT * FROM Users WHERE Name ="" or ""="" AND Pass ="" or ""=""

Since the OR “=” command is true, the query will provide access to all rows from the table named “Users” in the database.

So, these are a few examples of how SQL injection works. There are many other ways that hackers can use to exploit SQL injection vulnerabilities to break into your databases. You need an effective vulnerability management strategy to combat such threats to keep your systems secure.

Types of SQL Injection Attacks

The following are the different SQL injection types.

In-band SQL Injection

It is also referred to as classic SQL injection in which a hacker uses the same communication channel for both attack and response. So, a communication channel like a web browser is used to launch an SQLi attack, and the same browser or channel is used to gather its result. It is an efficient and easy method of SQL injection attacks that make it quite common. This attack happens in two ways:

• Union-based SQLi: Hackers can exploit the “UNION” operator in SQL that combines the results of multiple queries.
• Error-based SQLi: The database produces errors due to this kind of injection attack that reveals critical information about the database structure.

Let’s understand SQLi examples here:

1) Detailed example of In-band SQL Injection - Authentication Bypass Using SQLi

To truly understand In-band SQL injections, let's look at a backend code snippet.

Consider a PHP web application, to enable a PHP web application to establish a connection with our database and begin utilizing MySQL database functionality through PHP MySQL syntax, we require the following code:

code

$db = new mysql(‘localhost’, ‘root’, ‘password’, ‘users’);  $query = “select * from logins”;  $result = $db->query($query);

The above php code connects to the database users by providing servername(localhost), username(root) and password (passwd). Next, we write a SQL query and store it in $query.

In the last line, the query's output is stored in $result.

Next, we consider a vulnerable ‘login’ PHP/MySQL code snippet:

code

$query = ‘SELECT * FROM users WHERE user=”’.$_GET[‘user’].’” AND pass=”’.$ GET[‘password’].”’);  $result = $db->query($query);

The frontend would send the following GET request to the webserver while login.

https://insecure-ecommerce.com/login?user=username&password=topsecretpassword

In the php code, we use ‘.$_GET[‘user’].’ and ‘.$_GET[‘password’].’ to retrieve user input from the GET request.

Concept of Injecting Direct sql Code and Comments:

• The idea wherein we inject and craft our input using special characters in such a way that we can exit the user input logic of backend and are directly able to inject actual SQL code to the database.
• SQL allows for comments using – , # and /* */.
  - and # are used for inline comments.
  /* */ are used for multiline comments.

The server effectively ignores everything after the comment.

Now, for our vulnerable application logic, if we add a double quote (“) in our user input, it will end the user input field for the backend logic, and we can write directly inject actual SQL code.

For example, if we input admin as user and whatever” OR 1=1 ; -- as password.

The variables would contain:

$_GET['user'] = admin  $_GET['password'] = whatever” OR 1=1 ; -- “

The resulting query becomes:

SELECT * FROM users WHERE user="admin" AND pass= “whatever” OR 1=1 ;  -- “

Analyzing the above query, we can note the following observations:

pass=”whatever” is FALSE,

user=”admin” is TRUE

1=1 is always TRUE

In most SQL implementations, AND has precedence over OR.

Therefore, we can replace the where clause as:

• (TRUE AND FALSE) OR TRUE

• FALSE OR TRUE

• TRUE

Thus, the query will evaluate as TRUE even when the supplied password is invalid.

Effectively the sql command runs:

SELECT * FROM users WHERE user=”admin”

In turn, this would return data about the admin user. The injection in the $_GET['pass'] parameter is enough to make the MySQL server select the admin user and grant us access to that user.

2) Example of In-band SQLi - Using SQLi to Access hidden data

Retrieving hidden data

Imagine an e-commerce application that displays products in different categories. When the user clicks on the Premium category, their browser requests the URL:

https://insecure-ecommerce.com/products?category=Premium

This causes the application to make a SQL query to retrieve details of the relevant products from the database:

SELECT * FROM products WHERE category = 'Premium' AND released = 1

This SQL query asks the database to return:

• all details (*)
• from the products table
• where the category is Premium
• and released is 1.

The restriction released = 1 is being used to hide products that are not released. We could assume for unreleased products, released = 0.

The application doesn't implement any defenses against SQL injection attacks. This means an attacker can construct the following attack, for example:

https://insecure-ecommerce.com/products?category=Premium'--

The above URL results in the following backend SQL query:

SELECT * FROM products WHERE category = 'Premium'--' AND released = 1

Crucially, note that -- is a comment indicator in SQL. This means that the rest of the query is interpreted as a comment, effectively removing it. In this example, this means the query no longer includes AND released = 1. As a result, all products are displayed, including those that are not yet released.

You can use a similar attack to cause the application to display all the products in any category, including categories that they don't know about:

https://insecure-ecommerce.com/products?category=Premium'+OR+1=1--

The above URL results in the following backend SQL query:

SELECT * FROM products WHERE category = 'Premium' OR 1=1 --' AND released = 1

The modified query returns all items where either the category is Premium, or 1 is equal to 1. As 1=1 is always true, the query returns all items even the ones that are hidden and not publicly visible.

3) Example of Union-based SQLi - Retrieve data from other tables

Before we take a look into retrieving data from other database tables using Union-based SQLi, we need to understand the concept of Union query in SQL.

The concept of Union:

• The Union clause in SQL is used to combine results from multiple SELECT statements. This means that through a UNION injection, we will be able to SELECT and dump data from multiple tables and databases across the DBMS.
• UNION combines the output of two SELECT statements into one, so entries from table1 and table2 are combined into a single output with combined rows.

Note: A UNION statement can only operate on SELECT statements with an equal number of columns.

Now, let's move to Retrieving data from other tables from the database.

In cases where the application responds with the results of a SQL query, an attacker can try to retrieve data from other tables within the database. We can use the UNION query to execute an additional SELECT query and append the results to the original query.

For example, if an application executes the following query containing the user input Premium:

SELECT name, description FROM products WHERE category = 'Premium'

An attacker can submit the input:

' UNION SELECT username, password FROM users--

This causes the application to return all usernames and passwords along with the names and descriptions of products.

Inferential SQL Injection

Blind SQLi is another term used for this kind of attack. In this method, hackers will send data payloads to the target database server and examine its behavior and response thereafter. The hackers will attempt to learn more about the database structure and vulnerabilities based on the response and behavior. They can adjust the attack strategy based on the inferences from their observations.

Blind SQL injection attacks can be of two types:

• Time-based: In this method, the hacker relies on the time (in seconds) the database takes to respond to a query to determine whether it is true or false. The hacker sends a query to the database forcing it to wait for a specific before responding. This time indicates whether the query was false or true.
• Boolean-based: In this attack type, the hacker examines the behavior of the application and the database server after sending queries with malicious code combined using Boolean operators.

Example of Blind SQLi – Time based SQL injection

Many instances of SQL injection are blind vulnerabilities. This means that the application does not return the results of the SQL query or the details of any database errors within its HTTP responses. Blind vulnerabilities can still be exploited and escalated, but the techniques involved are generally more complicated and difficult to perform.

In a nutshell, you can’t see the results of the query or the errors, but you can distinguish between when the query returned a true or a false response based on the different content on the page.

Several ways to detect a blind sql injection are:

• You can change the logic of the query to trigger a detectable difference in the application's response depending on the truth of a single condition. This might involve injecting a new condition into some Boolean logic, or conditionally triggering an error such as a divide-by-zero.

• You can conditionally trigger a time delay in the processing of the query. This enables you to infer the truth of the condition based on the time that the application takes to respond.

• You can trigger an out-of-band network interaction, using OAST techniques. This technique is extremely powerful and works in situations where the other techniques do not. Often, you can directly exfiltrate data via the out-of-band channel. For example, you can place the data into a DNS lookup for a domain that you control.

Let's look at one such way: Exploiting blind SQL injection by triggering time delays:

It is often possible to exploit the blind SQL injection vulnerability by triggering time delays depending on whether an injected condition is true or false. As SQL queries are normally processed synchronously by the application, delaying the execution of a SQL query also delays the HTTP response. This allows you to determine the truth of the injected condition based on the time taken to receive the HTTP response.

In MySQL, the SLEEP function can be used

SELECT * FROM table  WHERE id=1-SLEEP(15)

If an average request typically takes 2 seconds to execute, introducing a sleep function and observing a response delay exceeding 15 seconds (in our example) indicates a vulnerability to blind SQL injection within the application.

Out-of-band SQL Injection

Hackers utilize this type of SQLi attack only when Inferential and In-band attacks are not possible. This type of attack can occur only when certain functionality is enabled on the target database. Out-of-band SQLi is an ideal attack when the server is too slow to respond, or the hacker cannot use the same channel to gather responses. The hacker exploits DNS and HTTP responses in this case to attempt attacks.

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What Can Attackers do with SQL Injection Attacks?

Attackers actively scan applications for SQLi flaws because the payoff can be huge. Below are the common outcomes of a successful SQL injection, ordered from most frequent to most destructive.

Data Retrieval

Attackers can read sensitive records, including usernames, emails, hashed passwords, PII, or financial data, by forcing queries to return information they shouldn’t see.

Why it matters: Data theft is often the first step in fraud, credential stuffing, or extortion.

Quick mitigation: Prevent it with parameterized queries and strict least-privilege DB accounts.

Data Exfiltration

Beyond reading small datasets, attackers can copy large volumes of data out of your database to servers they control. This often happens quietly and at scale.

Why it matters: Mass leaks cause regulatory fines and reputational damage.

Quick mitigation: Monitor unusual outbound traffic and restrict DB egress where possible.

Data Manipulation and Deletion

Attackers can insert, modify, or delete records — corrupting business data, changing transaction histories, or planting malicious entries.

Why it matters: Data corruption undermines trust and can break business workflows.

Quick mitigation: Enforce role-based access, maintain immutable logs, and have backups/versioning.

Authentication Bypass

By altering authentication queries, attackers can bypass login checks and impersonate users without credentials.

Why it matters: Attackers gain direct account access and can pivot inside the app.

Quick mitigation: Use prepared statements and add multi-factor authentication (MFA) for sensitive accounts.

Privilege Escalation

Once inside, attackers may escalate privileges within the database (or application) to gain administrative capabilities.

Why it matters: Admin-level access lets attackers read or change anything in the system.

Quick mitigation: Apply least-privilege principles and separate duties for DB admin accounts.

Remote Code Execution

Some database engines or misconfigurations allow SQL commands to trigger OS-level actions or load external procedures — enabling arbitrary code execution on the host.

Why it matters: This converts a data breach into a full server compromise.

Quick mitigation: Disable unsafe DB features, harden DB server configuration, and isolate DB hosts.

Denial of Service

Attackers can craft queries that overload the database (expensive joins, loops, or sleep-based blind injections), causing slowdowns or crashes.

Why it matters: Availability outages can halt business operations.

Quick mitigation: Add query timeouts, rate limits, and monitor query performance.

Business Impact of SQL Injection Attacks

A single SQL injection vulnerability can trigger far more than a technical failure. In fact, it can disrupt business operations, damage brand trust, and expose organizations to legal and financial consequences.

Here’s how SQLi attacks impact enterprises beyond the code layer.

Reputation Damage

Every breach erodes trust. When attackers exploit SQL vulnerabilities to steal sensitive customer data, such as PII, credentials, or payment details — it directly undermines your brand’s credibility. Customers expect confidentiality; once that’s broken, rebuilding confidence can take years.

Financial and Operational Loss

SQL injection incidents often lead to direct financial hits, from regulatory fines and legal fees to incident response costs and compensation programs.

Operational downtime during containment and recovery also interrupts revenue-generating services, sometimes costing millions in lost productivity.

Regulatory and Compliance Penalties

Data privacy laws like GDPR, CCPA, and PCI DSS impose strict data protection requirements. A successful SQLi breach that exposes personal or financial data can result in steep penalties and mandatory breach disclosures, amplifying reputational damage.

Data Integrity and Manipulation

Once attackers gain database access, they can alter, delete, or insert data, compromising the accuracy of reports, transactions, and analytics.

For data-driven organizations, this means decision-making based on corrupted information and potentially long-term business disruption.

Privacy Violations and Data Exposure

Attackers may publish or sell exposed user data on underground markets, violating privacy laws and putting customers at risk of identity theft. Such incidents not only harm individuals but also invite lawsuits and compliance scrutiny.

How SQL Injections Can Become More Dangerous Using Bots?

Let's see how SQL injections can exploit AI bots and make the impact even more dangerous.

Automated Input Testing

With the help of bots, attackers can systematically input multiple SQL payloads into web app fields like login forms or search bars. That's performed to assess potential vulnerabilities for exploitation.

Payload Injection

As soon as the vulnerability is found, bots inject malicious SQL code to misuse the application's database queries. The attackers manipulate database queries by altering them, bypassing authentication, or performing administrative operations.

Data Extraction

Bots can use the injected SQL commands to extract confidential data from the database, like users' credentials or other types of private details. Attackers execute this generally by automating queries that disclose such information.

Exploitation and Maintenance

The advanced bots need initial accessibility obtained through SQL injection to set up backdoors, which allows attackers to continue to exploit and retrieve the data.

Tips for SLQ Injection Prevention

While you can leverage a web app pentesting tool to discover a myriad of vulnerabilities, keeping it secure from the bottom is a more effective measure. Hence, injection attacks can be avoided by following the right coding practices and other methods. The following are some ways to prevent SQL injection attacks.

Pro Tip: If you are using Laravel technology, you can refer to our article to prevent SQL injection. Read More.

Use Parameterized Queries

It’s a way to sanitize the inputs by separating them from queries. It prevents the inputs from being injected directly into the SQL queries. The use of parameters for queries reduces the potential risk of manipulation. Parameters are values resolved at the execution time. Let’s see the example pseudocode below.

id = request.POST[‘userId’]  user_sql = "SELECT * FROM Users WHERE id = @id";  database.execute(user_sql, id);

In the above statement, you can see the parameter is used for ‘id’ input and it starts with the ‘@’ marker. Instead of directly providing inputs into the query, it is passed as a parameter to the execution function.

Use Input Validation

Set up input validation to prevent malicious code or commands. User input fields must accept only certain types of inputs. For example, a field that requires alphanumeric data to be passed should only accept and process that type of data and prevent others. Input validation will help to check whether the data falls into the range of acceptable data sets.

Escape User Inputs

There are some characters in a structured query language that hold special meanings like “*” implies “any” and “OR” is used for conditional statements. Hence, a special check is needed for these words. Here escaping the user input is useful. By escaping a character, you tell the database to treat it as literal and not pass it as a command.

Focus on Least Privilege

You should follow the “no trust” policy to ensure optimum security. Make sure only valid users can access the sensitive data and restrict administrative privileges. Reduce the number of permissions to the narrowest possible scope to avoid revealing sensitive data.

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Adopt the Best Defense

You must work with a data-centric approach for optimal protection of your data, network, and applications. Here you can leverage a layered approach in spreading your defense on multiple levels. Besides this, you should also perform vulnerability assessment to discover potential weaknesses that make your web app susceptible to structured SQLi attacks.

Regular vulnerability scanning helps you identify emerging threats and keep your systems secure with a strategic AppSec process. Moreover, you would need the best tips to choose the right SQL injection scanner that can detect vulnerabilities accurately with near-zero false positives.

ZeroThreat is the best vulnerability scanner that you can utilize to dynamically test your applications to detect weaknesses. This tool offers the fastest scanning speed and provides the highest accuracy to reduce efforts in manual pen testing. ZeroThreat gives you the right results with near-zero false positives and priority-based reports.