What is cross-site scripting (XSS)?

Cross-site scripting (XSS) is a security vulnerability that allows attackers to inject malicious scripts into web pages viewed by other users. It typically occurs when a web application incorporates untrusted data into a web page without proper validation or escaping. This vulnerability can lead to a range of malicious outcomes, including the theft of session cookies, unauthorized access to user accounts, and the distribution of malware.

When an attacker successfully carries out an XSS attack, the injected script runs in the browser of anyone viewing the compromised page. This can enable the attacker to manipulate content, redirect users to harmful sites, or gather sensitive information without the victim's knowledge.

Understanding XSS is crucial for web developers and security professionals, as it highlights the importance of input validation, output encoding, and implementing security measures to protect users from these types of vulnerabilities.