What is a cross-site scripting (XSS) attack?

A cross-site scripting (XSS) attack is defined as an attack that injects malicious client-side scripts into web pages viewed by users. This type of vulnerability arises when an application allows users to include data that can execute scripts in the browser of another user.

The core of XSS lies in the execution of scripts run in the context of a user's session, which can lead to consequences such as stealing session cookies, redirecting users to malicious sites, or performing actions on behalf of the user without their consent. This issue stands apart from other types of attacks because it doesn't require server-side vulnerabilities. Instead, the focus is on client-side interactions, making it a unique and prevalent threat in web security.

Other choices describe security concepts but do not accurately capture the nature of XSS. For instance, the option linking to server-side vulnerabilities pertains more to SQL injection attacks and other similar exploits aimed at compromising database integrity rather than client-side script execution. The option about securing web applications from unauthorized access relates more to defensive measures rather than an attack. Lastly, the technique for intercepting encrypted data pertains to different forms of security attacks, like man-in-the-middle attacks, and does not apply to the execution of scripts within the browser context of the user.