Cross-Site Scripting (XSS) - Basics and Prevention

Cross-Site Scripting (XSS) is a type of web security vulnerability where malicious scripts are injected into trusted websites. Hackers take advantage of web applications with input validation or encoding errors, which can lead to security vulnerabilities. When a user visits the compromised site, the browser unknowingly executes the injected script, giving the attacker access to sensitive information, such as cookies and session tokens.

There are varying degrees of complexity when it comes to exploiting XSS. The three types of XSS are DOM-based, stored, and reflected. In this brief reflection, I will focus on the fundamentals, including definitions, consequences, and prevention measures.

Consequences of XSS

XSS vulnerabilities can lead to several severe consequences for web applications and users:

Data Theft - Attackers can steal sensitive data, including login credentials, personal information, and financial details. 

Unauthorized Access - Malicious scripts can hijack user sessions, allowing attackers to gain unauthorized access to user accounts.

Website Defacement - Attackers can rewrite the content of a compromised web page, altering its appearance and delivering malicious content.

Phishing Attacks - XSS can be used to trick users into divulging their information on fake forms, leading to phishing attacks.

Browser Exploitation - XSS can exploit web browsers, leading to browser crashes or other undesirable behaviors.

Preventing XSS as a User

I now have a better understanding of how this type of situation could occur and what it may look like in the real world. However, for those who are inexperienced, it can be difficult to recognize the signs of exposure or compromise. What does it actually look like? How can we tell if we have been affected? Even if we don't realize it at the time, there are some indicators we can use to identify a potential future issue, such as:

  • Educate Yourself About Phishing Tactics:  Learn how phishing attacks work and familiarize yourself with common tactics used by attackers to trick users into revealing sensitive information. 

It is important for you to read the emails from IT that are addressed to you; they are seriously important for your organization.

  • Use Strong, Unique Passwords: Create strong and unique passwords for your accounts.
  This reduces the risk of attackers gaining access to your accounts even if they manage to gather some information.

  • Check Website URLs Carefully: Always double-check the URL of the website you're visiting.

 Phishing sites often use URLs that closely resemble legitimate ones.

Preventing XSS as a Developer

In order to prevent the occurrence of XSS vulnerabilities, developers should adhere to recommended practices and avoid adopting harmful patterns. But what does it mean exactly?

Input validation: Validate and sanitize anything coming from the user and I mean it! treat every user as a potential attacker. 

Currently, there are numerous libraries and frameworks available that can protect against harmful input. It only requires a short amount of time to conduct proper research and select the best option for our software requirements. C'mon everyone, we got this, Let's develop from a security point of view.

Output encoding: Encoding the dynamic content of our applications before is displayed in the browser prevents script execution. This is a bit hard to understand but fundamentally it is not. Code that is rendered on the browser will execute, so avoid having it run and will avoid having bad actors exploiting our code.

Again, many libraries and frameworks aim to help with this by design. MAKE USE OF THEM.


Cross-Site Scripting (XSS) is a web security vulnerability that can be extremely dangerous. It allows attackers to inject malicious scripts into web applications, which can have devastating consequences, regardless of how the application is being used.

As users, we need to be aware of a few simple things we can do to avoid falling victim to attackers who exploit XSS on websites or applications. And as developers, we have an even greater responsibility to ensure the safety of our users. 

I will continue the XSS saga as is the current topic I'm working on.

Happy bug-hunting!


Yaworski, P. (2019). Real-world bug hunting: A field guide to web hacking. No Starch Press.

Kohnfelder, Loren. (2022). Designing Secure Software : A Guide for Developers. No Starch Press.