Learning SQL Injection Through a Login Bypass Lab (PortSwigger Walkthrough)

One of the best ways I've found to learn web application security is by working through hands-on labs. Recently, I completed the PortSwigger Web Security Academy lab called "SQL Injection Vulnerability Allowing Login Bypass."

Even though this is an introductory lab, it demonstrates a vulnerability that has historically led to some serious real-world security incidents.

The Goal

The objective was simple: log in as the administrator user without knowing the password.

The application contained a SQL Injection vulnerability in its login functionality, making it possible to manipulate the backend SQL query.

Understanding the Vulnerability

When a user logs in, the application typically checks the provided username and password against records stored in a database.

A vulnerable query might look something like this:

SELECT * FROM users
WHERE username = 'administrator'
AND password = 'password123';

SELECT * FROM users
WHERE username = 'administrator'
AND password = 'password123';

If user input is inserted directly into the query without proper protection, an attacker can change the logic of the SQL statement.

That's exactly what happened in this lab.

Finding the Injection Point

I navigated to the login page and tested the username field.

For the username, I entered:

administrator'--

administrator'--

The password field could contain any value.

The apostrophe closes the username string, and the double dash (--) comments out the rest of the SQL query, including the password check.

As a result, the application effectively processes a query that only checks whether the username is "administrator."

The Result

After submitting the request, I was successfully logged in as the administrator user.

No valid password was required.

This demonstrates how a small coding mistake can completely break an application's authentication system.

What I Learned

This lab reinforced a few important lessons:

• Never trust user input.
• Authentication mechanisms are high-value targets for attackers.
• SQL Injection remains relevant despite being a well-known vulnerability.
• Parameterized queries are one of the most effective ways to prevent this issue.

Final Thoughts

Although this was a beginner-level lab, it highlights why secure coding practices matter. A single vulnerable input field can lead to unauthorized access and potentially much larger security issues.

I'm continuing my journey through PortSwigger's labs to strengthen my understanding of web application security and common attack techniques.

If you're learning application security, I highly recommend getting hands-on experience with labs like these. Reading about vulnerabilities is helpful, but exploiting them in a safe environment helps the concepts stick.

Thanks for reading, and feel free to connect if you're also exploring web security and penetration testing.