How To Test for SQL Injections – 2025 Guide

Anushree Chatterjee

Software Testing

“We’re all going to have to change how we think about data protection” — Elizabeth Denham.

More so with the AI chatbots, LLMs, and their integration with almost every app. Imagine a scenario where a hacker manipulates a login form to access sensitive customer data from an e-commerce platform’s database. This isn’t just theoretical – it happened to TalkTalk, a UK-based telecom company, in 2015. Hackers exploited a simple SQL injection flaw to steal the personal information of over 150,000 customers, leading to millions in fines and irreparable damage to the company’s reputation.

In today’s digital age, where websites and apps handle everything from personal information to financial data, SQL injection remains one of the most dangerous vulnerabilities in web security. In this article, we will look at this security threat and ways to test it.

What is SQL Injection?

SQL Injection, often abbreviated as SQLi, is a type of security vulnerability that allows attackers to interfere with the way a web application communicates with its database. To put it simply, it’s like a hacker tricking the website into running unauthorized commands on the database. This can lead to data theft, data loss, or even gaining complete control over the application.

Think of it this way: When you fill out a form on a website, like a login page or a search box, your input is sent to the database as a query to get or update information. If the website is not properly secured, a hacker can input malicious code instead of the expected text. This code manipulates the query in a way that the database executes unintended commands.

How Does SQL Injection Work?

SQL Injection (SQLi) works by exploiting a vulnerability in a web application’s interaction with its database. It allows an attacker to inject malicious SQL code into a query, tricking the database into performing actions it was never intended to do. Here’s a simple explanation of how it works:

How Web Applications Use SQL?

Web applications often need to interact with a database to retrieve, update, or delete information. For example:

Logging in requires checking if the username and password exist in the database.
Searching requires querying the database for matching records.

The application sends SQL queries to the database, like:

SELECT * FROM users WHERE username = 'johndoe' AND password = 'mypassword';

This query checks if a user with the username “johndoe” and password “mypassword” exists.

Where the Vulnerability Lies?

The vulnerability happens when the web application doesn’t properly validate or sanitize user inputs before including them in SQL queries. If an attacker enters unexpected input, it can change the SQL query’s meaning and make the database do things it shouldn’t.

For example:

If the application simply takes the username and password from the user and directly plugs them into the query:

SELECT * FROM users WHERE username = 'user_input' AND password = 'user_password';

The attacker can insert SQL code as part of the input.

SQL Injection Example

Let’s use a login form to explain how an attacker might exploit this.

Normal Behavior

The user enters:

Username: johndoe
Password: mypassword

The application creates a query:

SELECT * FROM users WHERE username = 'johndoe' AND password = 'mypassword';

If this query finds a match in the database, the user is logged in.

Attacker’s Input

An attacker enters:

Username: ‘ OR ‘1’=’1
Password: anything

The query becomes:

SELECT * FROM users WHERE username = '' OR '1'='1' AND password = 'anything';

Here’s what happens:

username = ” checks for an empty username.
OR ‘1’=’1′ always evaluates to true.
The database doesn’t need to check the password because the query logic is already satisfied.

As a result, the attacker bypasses authentication and logs in without valid credentials.

SQL Injection Test: Advanced Exploits

SQL Injection doesn’t stop at bypassing logins. Here are more advanced ways attackers can use SQL Injection:

Data Theft: The attacker injects SQL to extract sensitive information, like customer details or credit card numbers.
- Input: ' UNION SELECT username, password FROM users--
- Resulting query: SELECT * FROM users WHERE username = '' UNION SELECT username, password FROM users;
- This merges data from another table (users) into the response.
Data Manipulation: The attacker injects SQL to modify or delete records.
- Input: ' ; DROP TABLE users;--
- Resulting query: SELECT * FROM users WHERE username = ''; DROP TABLE users;
- This deletes the entire ‘users’ table.
Privilege Escalation: The attacker injects SQL to gain administrative access.
- Input: ' ; UPDATE users SET role = 'admin' WHERE username = 'john';--
- Resulting query: SELECT * FROM users WHERE username = ''; UPDATE users SET role = 'admin' WHERE username = 'john';
Database Takeover: The attacker executes operating system commands or installs malicious software through the database.
- Input: ' ; EXEC xp_cmdshell('dir');-- (for Microsoft SQL Server)
- Resulting query: SELECT * FROM users WHERE username = ''; EXEC xp_cmdshell('dir');
- This lists server files.

Why Does This Work?

SQL Injection works because:

Input is trusted: The application doesn’t properly validate or sanitize what the user inputs.
SQL queries are dynamic: The input is directly included in the query without being treated as data separate from the command.
Errors reveal information: In some cases, error messages or unexpected behavior give attackers clues about how the database works.

Different Types of SQL Injection (SQLi)

SQL Injection attacks come in various forms, each with unique techniques and objectives. Here are the most common types of SQL injections:

Classic SQL Injection (In-Band SQL Injection)

This is the most straightforward type of SQL Injection. The attacker sends malicious SQL code through an input field or URL, and the results are immediately visible in the application’s response.

Steps to Execute:

The attacker exploits a vulnerable input field (e.g., a login form or search box).
The database executes the malicious code, and the results (like sensitive data) are displayed on the screen.

Example:

Suppose a search bar accepts user input without validation. If the attacker enters:

' OR '1'='1

The database might execute the following:

SELECT * FROM products WHERE name = '' OR '1'='1';

This query returns all records because 1=1 is always true.

Use Case:

Data theft, like extracting usernames, passwords, or credit card details.

Blind SQL Injection

In this type, the attacker can’t see the database’s response directly but infers information by observing changes in the application’s behavior (e.g., page content, HTTP status codes, or delays).

Types of Blind SQL Injection:

Boolean-Based Blind SQL Injection: The attacker asks yes/no questions by injecting SQL, which changes the query’s outcome.

Example: Injecting ' AND 1=1-- (true condition) may return a normal page, while ' AND 1=2-- (false condition) may show an error.
Time-Based Blind SQL Injection: The attacker uses SQL commands to delay the database’s response.

Example: If the page takes longer to load, it indicates the condition is true.
```
' OR IF(1=1, SLEEP(5), 0)--
```

Use Case:

Used when error messages or results are not visible but the application behavior can be observed.

Error-Based SQL Injection

This type relies on database error messages to extract information. The attacker intentionally creates errors in SQL queries and uses the error details to gather sensitive information about the database structure.

Steps to Execute:

The attacker inputs SQL, which triggers an error and exposes database information like table names or column details.

Example:

Injecting:

' AND 1=CONVERT(int, (SELECT @@version))--

The database may return an error message revealing the database version.

Use Case:

Quickly gathering information about the database schema to plan further attacks.

Union-Based SQL Injection

This technique uses the UNION SQL operator to combine the results of multiple queries into a single response. Attackers use it to extract data from other tables.

Steps to Execute:

The attacker appends a UNION query to the original SQL command to fetch data from a different table.

Example:

' UNION SELECT username, password FROM users--

This query combines the original results with data from the ‘users’ table, showing usernames and passwords.

Use Case:

Extracting data from other tables in the database.

Time-Based SQL Injection

A form of Blind SQL Injection where attackers delay the database response based on the injected SQL command. The response time helps infer whether a condition is true or false.

Steps to Execute:

The attacker inputs SQL, which includes a time delay (e.g., SLEEP or WAITFOR).
If the page takes longer to load, it confirms the injected condition.

Example:

' OR IF(1=1, SLEEP(5), 0)--

If the page is delayed by 5 seconds, the condition (1=1) is true.

Use Case:

Testing conditions and extracting information when no visible errors or responses are available.

Second-Order SQL Injection

In this advanced type, the attacker injects malicious SQL into a system that stores the input. The payload is executed later when another query processes the stored data.

Steps to Execute:

The attacker inputs malicious data into a field that gets stored in the database (e.g., during user registration).
Later, when the stored data is used in another query, the payload is executed.

Example:

During user signup, the attacker inputs:

John'; DROP TABLE users;--

If the application uses this stored value in a query later, it executes the malicious code.

Use Case:

Targeting back-end systems or delayed exploitation.

Here’s a summary of the classifications of SQL injections.

How to Test for SQL Injection?

Remember the types of SQL injections that we saw above? You need to use those to test your application for SQLi. This means that you need to try to inject malicious SQL code into user input fields, URLs, or other data sources to see if the application behaves unexpectedly. You can do this manually or via automation.

Here’s how you can go about it:

Preparation

For preparation, you need to execute the following steps first.

Step 1: Understand the Application

Identify parts of the application that interact with a database, such as:

Login forms
Search boxes
Query parameters in URLs
Filters, dropdowns, or sorting options

Check for places where the application takes user input.

Step 2: Set Up a Safe Testing Environment

Never test on live systems unless you have explicit permission. Instead, use a controlled environment, such as a test version of the application.

Step 3: Choose Your Tools

You can test manually or use automated tools like:

SQLmap: Automates SQL Injection testing.
Burp Suite: Intercepts and manipulates HTTP requests.
OWASP ZAP: A free web application security scanner.

Manual Testing

Manual testing involves directly entering SQL Injection payloads into input fields or modifying URLs. We will check for the different types of SQLi vulnerabilities. Here’s how you can do it:

Step 1: Test for Basic SQL Injection

Enter simple SQL characters like:

‘
“
—
;

Observe the application’s behavior. Look for:

Error messages like “SQL syntax error” or “unclosed quotation mark.”
Unexpected changes in the application’s output.

Example:

Input: ‘
Response: An error like: “You have an error in your SQL syntax near ” at line 1”
This indicates the application may be vulnerable.

Step 2: Test Using Boolean Logic

Input conditions to check if the application evaluates them.

Example:

Input into a search box: ' OR 1=1--
What it does: OR 1=1 always evaluates to true.
Expected behavior: If the application shows all results instead of a filtered set, it’s likely vulnerable.

Step 3: Test Using Time Delays

Inject a payload that causes the database to pause if a condition is true.

Example:

If you input code: ' OR IF(1=1, SLEEP(5), 0)--
What it does: Delays the response for 5 seconds if the condition is true.
Expected behavior: If the response takes longer, the application might be vulnerable.

Step 4: Test Using UNION Queries

Check if the application combines results from different tables using the UNION operator.

Example:

If you input code: ' UNION SELECT NULL, NULL--
Gradually increase the number of NULL values to match the number of columns in the query.
Once successful, replace NULL with actual data like: ' UNION SELECT username, password FROM users--

Step 5: Explore Error Messages

Enter complex payloads to intentionally cause errors.

Example:

If you input code: ' AND 1=CONVERT(int, @@version)--
What it does: Tries to convert the database version into an integer, causing an error.
Expected behavior: Reveals database details like the version or structure.

SQL Injection Tools

Instead of manually injecting and observing results for every possible vulnerability, automated testing tools can scan input fields, query parameters, and other potential entry points for SQLi to save you time and effort.

Here are some of the most commonly used security testing tools:

SQLmap

SQLmap is one of the most popular tools for testing SQL Injection. It’s powerful, open-source, and automates the entire process.

Key Features

Identifies SQL Injection vulnerabilities.
Automatically determines the type of SQL Injection (e.g., error-based, time-based, UNION-based).
Extracts data like table names, column names, and records.
Can exploit vulnerabilities to retrieve data or even execute database commands.

Burp Suite

This is a widely used web application security tool that includes features for SQL Injection testing.

Key Features

Intercepts and manipulates HTTP requests to test for vulnerabilities.
Includes an Intruder tool for automating SQL Injection attacks.
It can scan applications and highlight potential SQL injection points.

OWASP ZAP (Zed Attack Proxy)

This is a free, open-source tool for testing web application security.

Key Features:

Automatically scans web applications for vulnerabilities, including SQL Injection.
Allows manual testing with an intercepting proxy.
Provides pre-configured SQL Injection payloads for testing.

Mitigation and Prevention of SQL Injection

SQL injection is one of the most common and dangerous web vulnerabilities, but the good news is that it’s entirely preventable with proper coding and security practices.

Use Parameterized Queries (Prepared Statements)

This is the most effective way to prevent SQL Injection. Parameterized queries ensure that user inputs are treated as data, not executable code.

What Does it Mean?

Instead of directly embedding user input into SQL commands, you use placeholders for the input, and the database automatically handles it safely.

Example Without Protection (Vulnerable):

SELECT * FROM users WHERE username = '" + userInput + "' AND password = '" + userPassword + "';

Example With Protection:

query = "SELECT * FROM users WHERE username = ? AND password = ?"
cursor.execute(query, (userInput, userPassword))

Here, the database safely handles the inputs, so even malicious inputs won’t alter the query.

Validate and Sanitize User Inputs

All user inputs – whether from forms, URLs, or cookies – should be validated and sanitized to ensure they meet the expected criteria.

Steps to Sanitize Inputs:

Define Input Rules: For example, usernames should only contain letters and numbers.
Strip Out Special Characters: Remove or escape characters like ‘, “, ;, and –.
Reject Suspicious Inputs: Block inputs with SQL keywords like SELECT, DROP, or UNION.

Use Stored Procedures

Stored procedures are precompiled SQL queries stored in the database. They execute fixed SQL commands with parameters, reducing the risk of SQL injection.

CREATE PROCEDURE GetUser (@username NVARCHAR(50), @password NVARCHAR(50))
AS
BEGIN
  SELECT * FROM users WHERE username = @username AND password = @password
END

Since the logic is fixed, it’s harder for attackers to manipulate.

Implement the Least Privilege Principle

Only give the database user account the minimum permissions required for its job. For example:

A user account used for login functionality doesn’t need permission to DROP or DELETE tables.
This limits the damage even if an SQL Injection vulnerability exists.

Use a Web Application Firewall (WAF)

A Web Application Firewall acts as a protective shield between your application and the internet. It monitors and blocks malicious requests, including SQL injection attempts.

Avoid Displaying Database Error Messages

Error messages can reveal valuable information about your database, such as table names, column names, or the database version.

What to Do?

Disable Detailed Error Messages: Configure the application to show generic error messages like Something went wrong instead of detailed SQL errors.
Log Errors Privately: Log errors to a secure location for debugging, but don’t expose them to users.

Regularly Update and Patch Systems

Outdated software often has known vulnerabilities, such as SQL injection weaknesses. If the system isn’t updated, hackers can exploit these.

Use Input Escaping

When input sanitization isn’t possible, escaping special characters can help prevent SQL Injection by neutralizing potentially malicious inputs.

Conduct Regular Security Testing

Regularly test your application to identify and fix vulnerabilities before attackers can exploit them.

Types of Testing:

Manual Testing: Use tools like Burp Suite or test manually for vulnerabilities.
Automated Scanning: Tools like SQLmap or OWASP ZAP can help identify SQL Injection.
Penetration Testing: Hire ethical hackers to simulate real-world attacks.

Common Myths About SQL Injection Testing

Though SQLi is one of the oldest and most well-known web application vulnerabilities, misconceptions about testing it are still prevalent. Here are some of them:

Myth	Reality
SQLi only affects login pages or authentication forms.	SQLi can occur anywhere user input is processed by a database, not just login forms. (e.g., search, URLs, APIs)
Using modern frameworks like Django, Laravel, or Ruby on Rails automatically makes your application immune to SQLi.	While frameworks offer tools to prevent SQLi (like ORMs and parameterized queries), improper use of these tools can still introduce vulnerabilities. Secure coding practices are still necessary, even with modern frameworks.
SQLi is simple to spot and straightforward to resolve.	Some SQLi vulnerabilities, like Blind SQLi, are subtle and require careful observation to detect.
Automated tools like SQLmap, Burp Suite, or OWASP ZAP will help you find all possible SQLi issues.	Automated tools are helpful but not foolproof. They might miss complex or unusual attack vectors.
Only highly skilled hackers can perform SQLi attacks.	SQLi can be exploited with basic knowledge and widely available tools.
Validating user inputs is enough to prevent SQLi.	Validation helps but must be combined with parameterized queries and secure practices.
SQLi is only a risk for traditional SQL databases like MySQL or PostgreSQL.	Even NoSQL databases (like MongoDB or Elasticsearch) are vulnerable to injection attacks, though the syntax and techniques differ.
Fixing a single SQLi vulnerability means the application is secure.	Fixing one instance doesn’t guarantee there aren’t other vulnerabilities elsewhere in the code. SQL Injection can exist in multiple places, so testing must be ongoing.
Hackers only target large organizations or popular websites.	Small websites are often easier targets because they may lack robust security measures.
Encrypting sensitive data in the database prevents SQLi.	Encryption protects data at rest but doesn’t stop an attacker from exploiting a vulnerability to access or manipulate data.

Also read: OWASP Top 10 for LLMs: How to Test?

Conclusion

Understanding SQL Injection is crucial because it’s one of the easiest vulnerabilities to exploit if a website is not properly secured. Testing for SQL injection isn’t just about fixing bugs – it’s about protecting your users, business, and trust in the digital ecosystem. It’s also preventable with proper coding practices, which makes it a top priority for developers and security teams to address.

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