While testing the company's web applications, a tester attempts to insert the following test script into the search area on the company's web site: <script>alert(" Testing Testing Testing ")</script>

A buffer overflow involves writing data beyond a memory buffer's boundary to corrupt adjacent memory or execute arbitrary code - it is not triggered by injecting HTML or JavaScript into a form field.

Cross-Site Request Forgery (CSRF) tricks an authenticated user's browser into submitting unintended requests to a trusted site; it does not involve injecting or executing scripts within the application itself.

A Distributed Denial of Service (DDoS) attack overwhelms a target with traffic from multiple sources to deny availability; injecting a script tag into a search box is unrelated to service disruption.

Cross-Site Scripting (XSS) occurs when a web application accepts untrusted input and includes it in output without proper encoding or sanitization, causing the browser to execute it as script. The injected `<script>alert(...)` tag being rendered and executed as a pop-up confirms the application does not sanitize or encode user input, making it vulnerable to reflected or stored XSS attacks that could steal session cookies or redirect users.