This content originally appeared on DEV Community and was authored by founder of codemaster
Cross-Site Scripting (XSS) is one of the most common security vulnerabilities in web applications. Despite its simplicity, XSS can have serious consequences, allowing attackers to execute malicious scripts in users’ browsers. For developers and pentesters alike, understanding XSS is essential for building secure web applications and identifying vulnerabilities.
What is XSS?
XSS occurs when an attacker manages to inject malicious code, usually JavaScript, into a web page that other users visit. When the browser executes this code, the attacker can steal cookies, session tokens, or even manipulate the content of the page
There are three main types of XSS:
Stored XSS (Persistent XSS):
Malicious code is saved on the server, for example in a database, and served to users every time they visit the affected page.
Reflected XSS (Non-Persistent XSS):
The malicious code is part of the request (e.g., a URL parameter) and is reflected back by the server. This type is often delivered via phishing links.
DOM-based XSS:
The vulnerability exists entirely on the client side. JavaScript manipulates the DOM using untrusted input, and malicious scripts execute without ever touching the server.
How XSS Works?
At its core, XSS exploits the trust a browser has in the content served by a website. For example, consider a simple JavaScript snippet:
The root cause is unsanitized or unescaped user input being injected into the DOM or HTML content.
Why Developers Should Care
XSS isn’t just an academic problem—it affects real users:
Stealing session cookies can allow attackers to impersonate users.
Malicious scripts can redirect users to phishing pages.
Defaced content can damage your site’s reputation.
Understanding XSS helps developers write safer code and empowers pentesters to identify vulnerabilities before attackers do.
This content originally appeared on DEV Community and was authored by founder of codemaster
founder of codemaster | Sciencx (2025-11-14T16:47:55+00:00) Understanding XSS: A Beginner’s Guide for Developers and Pentesters. Retrieved from https://www.scien.cx/2025/11/14/understanding-xss-a-beginners-guide-for-developers-and-pentesters/
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