How To Test Sql Injection On Login Page

How To Articles

As a web developer, one of the most important aspects of building a secure application is preventing SQL injection attacks. SQL injection occurs when an attacker is able to manipulate an SQL query in a way that can lead to unauthorized access to the database or the leaking of sensitive information. In this article, I will guide you through the process of testing SQL injection on a login page, allowing you to identify and fix any vulnerabilities in your application’s security.

Before we begin, it’s important to note that testing SQL injection on a live website without permission is illegal and unethical. Always make sure you have proper authorization and are working on a test environment before attempting any security testing.

Understanding SQL Injection

To start, let’s briefly discuss what SQL injection is. When a login form is not properly secured, attackers can use special characters or SQL statements to manipulate the SQL query that is executed by the server. This can allow them to bypass the login process altogether or retrieve sensitive data from the database.

For example, consider a simple login form that takes a username and password as inputs:

<form action="/login" method="post">
<input type="text" name="username">
<input type="password" name="password">
<input type="submit" value="Login">

When the form is submitted, the server typically executes an SQL query similar to:

SELECT * FROM users WHERE username = 'input_username' AND password = 'input_password';

However, if the form inputs are not properly sanitized and the attacker enters something like ' OR '1'='1 as the username and an empty password, the resulting SQL query becomes:

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

Since '1'='1' always evaluates to true, the attacker is able to bypass the login check altogether and gain access to the system.

Testing for SQL Injection

Now that we understand the basics of SQL injection, let’s proceed with testing for it on a login page. Here are the steps:

  1. Identify the Login Form: Locate the HTML form element responsible for accepting the username and password inputs.
  2. Submit Valid Inputs: Start by submitting valid inputs to ensure that the login functionality is working as expected.
  3. Submit Single Quotes: Enter a single quote (‘) as the username or password. If the application is vulnerable, it might throw an error or behave unexpectedly.
  4. Submit SQL Statements: Try entering SQL statements such as OR '1'='1 or 1; DROP TABLE users; as the username or password. If the application is not properly secured, it may execute these statements and reveal sensitive information or perform unintended actions.
  5. Observe Error Messages: Check if the application displays any specific error messages that might reveal the underlying SQL query. These messages can be valuable for an attacker in constructing a successful SQL injection attack.


Let’s take a practical example. Suppose we have a login form that sends a POST request to /login endpoint.

On my test application, I would perform the following steps:

  1. Fill in the username and password fields with valid credentials, such as ‘admin’ and ‘password’.
  2. Login should be successful, indicating that the application is working as expected.
  3. Now, try entering a single quote (‘) as the username or password.
  4. If the application rejects the input or behaves unexpectedly, it may indicate a vulnerability to SQL injection.
  5. Next, try entering ' OR '1'='1 as the username or password.
  6. If the application grants access without a valid password, it is likely vulnerable to SQL injection.
  7. Lastly, check for any error messages that might reveal the underlying SQL query.


Testing for SQL injection vulnerabilities on a login page is crucial for ensuring the security of your application. By understanding the concept of SQL injection, identifying the login form, and carefully crafting malicious inputs, you can uncover any vulnerabilities and address them before they can be exploited by attackers.

Remember, ethical and responsible testing is essential to protect both your own application and the security of your users. Always ensure you have proper authorization and work in a controlled testing environment.

Stay vigilant and keep your applications secure!