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Introduction

Did you know that a simple website visit could put your personal information at risk? In this article, we explain how a common online threat called XSS can cause big problems and show you ways to keep your application secure. 

What is Cross-Site Scripting (XSS)?

Cross-site scripting (XSS) is a significant web security vulnerability that enables attackers to inject malicious scripts into content that other users see. This type of attack exploits a user’s trust in a particular site, allowing the attacker to send malicious code to an unsuspecting user through the web application. 

Unlike other web attacks, XSS does not directly target the web application itself; instead, it targets the web application’s users, making it uniquely dangerous and widespread.

There are three primary types of XSS attacks:

Stored XSS (Persistent XSS)

This occurs when a malicious script is permanently stored on the target server, such as in a database, message forum, visitor log, comment field, etc. The malicious script is executed every time a user accesses the stored data.

Example 1: Stored XSS

<!– A comment form on a blog post –>
<form action=“/submit_comment” method=“POST”>
    <textarea name=“comment”></textarea>
    <button type=“submit”>Submit Comment</button>
</form>

In a Stored XSS attack, an attacker might submit a comment that includes a malicious script like <script>alert(‘XSS’);</script>. Suppose the website properly sanitizes the input before displaying it to other users. In that case, the script will execute in the context of the user’s browser, potentially leading to session hijacking, data theft, or other malicious outcomes.

Reflected XSS (Non-Persistent XSS)

This happens when a malicious script is reflected off a web application to the user’s browser. It is typically delivered via email or another external link and tricks the user into submitting a request to a web application, which includes the attack in the response.

Example 2: Reflected XSS

<!– A search form –>
<form action=“/search” method=“GET”>