ช่องโหว่ด้านความปลอดภัยที่พบบ่อยและวิธีแก้ไข

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.

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.

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.

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.

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.

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 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.

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.

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.

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

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!