Spring Security 6 & JWT Authentication · Lesson

Common Security Vulnerabilities & Fixes

Identify and address common web application security vulnerabilities, such as XSS, CSRF, and SQL injection, within a Spring Security context.

Common Security Vulnerabilities & Fixes is a free Spring Security 6 & JWT Authentication lesson on CoddyKit — lesson 3 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the Spring Security 6 & JWT Authentication learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.

Web Vulnerabilities Overview

Welcome! In this lesson, we'll dive into common web application security vulnerabilities. Understanding these threats is crucial for building robust and secure applications.

Even with frameworks like Spring Security, knowing how common attacks work helps you write safer code and configure your app effectively.

What is Cross-Site Scripting?

Cross-Site Scripting (XSS) occurs when attackers inject malicious scripts (usually JavaScript) into web pages viewed by other users.

These scripts can steal session cookies, deface websites, or redirect users to phishing sites. It tricks the user's browser into executing untrusted code.

Reflected, Stored, and DOM XSS

XSS comes in a few flavors:

Reflected XSS: Malicious script is part of the request (e.g., URL parameter) and immediately 'reflected' back in the response.
Stored XSS: Malicious script is permanently stored on the target server (e.g., in a database via a comment field) and served to all visitors.
DOM-based XSS: The vulnerability lies in client-side code modifying the Document Object Model (DOM) based on user input, rather than server-side generation.

XSS Prevention: Input & Output

The best defenses against XSS are:

Input Validation: On the server, strictly validate and sanitize all user input. Don't trust anything coming from the client.
Output Encoding: Before displaying user-supplied data in HTML, always 'escape' it. This turns malicious code into harmless text, preventing the browser from executing it.

Spring frameworks often provide utilities for output encoding.

Encoding User Input

Here's a simple Java example demonstrating output encoding. Notice how special HTML characters like < and > are converted to their entity equivalents (<, >).

This makes the script harmless when rendered in a browser.

import org.springframework.web.util.HtmlUtils;

public class XssPrevention {
  public static void main(String[] args) {
    String userInput = "<script>alert('You are hacked!');</script>";
    String safeOutput = HtmlUtils.htmlEscape(userInput);

    System.out.println("Original: " + userInput);
    System.out.println("Encoded: " + safeOutput);
  }
}

What is Cross-Site Request Forgery?

Cross-Site Request Forgery (CSRF) is an attack that tricks a logged-in user into submitting a request they did not intend. For example, changing their password or making a purchase.

The attacker crafts a malicious web page that sends a request to your application, and if the user is logged in, their browser automatically includes authentication credentials (like cookies).

Spring Security's CSRF Defense

Spring Security provides robust, built-in CSRF protection. By default, it generates a unique, synchronized token (a CSRF token) for each session.

This token must be included in non-GET requests (like POST, PUT, DELETE). If the token is missing or invalid, Spring Security rejects the request, preventing CSRF attacks.

What is SQL Injection?

SQL Injection (SQLi) is a common attack where malicious SQL code is inserted into input fields to manipulate backend database queries.

Attackers can use SQLi to bypass authentication, retrieve sensitive data, modify data, or even take control of the database server. It's often exploited when an application constructs SQL queries using concatenated strings.

SQLi Prevention: Parameterized Queries

The primary defense against SQL Injection is using parameterized queries (also known as prepared statements).

Instead of concatenating user input directly into the SQL string, placeholders are used. The database then treats user input as data, not as executable SQL code, neutralizing the attack.

import java.sql.*;

public class SqlInjectionPrevention {
  public static void main(String[] args) {
    String username = "admin' OR '1'='1"; // Malicious input

    // GOOD: Parameterized Query (Safe concept)
    String goodSql = "SELECT * FROM users WHERE username = ?";
    System.out.println("Safe SQL (PreparedStatement concept): " + goodSql);
    System.out.println("Parameter used: " + username);
    // In a real app, 'username' would be set as a parameter
    // on a PreparedStatement object.
  }
}

Vulnerability Check

Which of the following is the most effective way to prevent SQL Injection attacks?

Lesson Summary

Great job! You've explored three critical web vulnerabilities and their fixes:

XSS: Prevent with input validation and output encoding.
CSRF: Spring Security handles this by default with CSRF tokens.
SQL Injection: Prevent with parameterized queries (prepared statements).

Always remember to validate all input, encode all output, and leverage your framework's built-in security features!

Frequently asked questions

Is the “Common Security Vulnerabilities & Fixes” lesson free?

Yes — the full text of “Common Security Vulnerabilities & Fixes” is free to read here on the web, and the Spring Security 6 & JWT Authentication course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the Spring Security 6 & JWT Authentication course, upgrade to CoddyKit PRO.

What will I learn in “Common Security Vulnerabilities & Fixes”?

Identify and address common web application security vulnerabilities, such as XSS, CSRF, and SQL injection, within a Spring Security context. You practise Spring Security 6 & JWT Authentication with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.

Do I need any experience to start Spring Security 6 & JWT Authentication?

No prior experience is required. Spring Security 6 & JWT Authentication on CoddyKit is structured for beginners through advanced learners; this is — lesson 3 of 4, so you can start here or from the beginning and move at your own pace.

How long does the “Common Security Vulnerabilities & Fixes” lesson take?

Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.

Can I write and run code in this Spring Security 6 & JWT Authentication lesson?

Yes. Every Spring Security 6 & JWT Authentication lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.

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