Cross-site scripting (XSS) is a prevalent web vulnerability that allows attackers to inject client-side scripts into web pages viewed by users, potentially leading to session hijacking, data theft, and manipulation of displayed content. Although XSS was previously listed as a top vulnerability by the OWASP, it has now been grouped under the broader category of Injection vulnerabilities, which still impact 94% of web applications tested. XSS can exploit various data sources rendered by browsers, making it a versatile and dangerous threat. It can be categorized into reflected and stored XSS, both of which require careful analysis of data flow and treatment to detect. Notorious incidents, such as the Samy worm and TweetDeck attack, highlight the persistent threat posed by XSS. Tools like Detectify can help identify such vulnerabilities through automated testing, while effective remediation involves sanitizing or escaping dangerous characters and employing security features like HttpOnly and Content Security Policy (CSP).