Which of the following is a common vulnerability in web applications?

Cross-site scripting (XSS) is a common vulnerability in web applications that occurs when an attacker injects malicious scripts into content that is then delivered to users. This vulnerability often arises when a web application fails to properly validate or sanitize user inputs before rendering them. Attackers can exploit XSS to execute scripts in the context of the user's browser session, leading to various harmful outcomes, such as stealing session cookies, redirecting users to malicious sites, or defacing web pages.

This vulnerability is particularly prevalent in environments where user-generated content is accepted, such as chat applications, forums, and comment sections. Understanding XSS is crucial for web developers and security professionals, as it emphasizes the importance of input validation and output encoding to safeguard web applications from such threats.

While other vulnerabilities like encryption flaws and buffer overflows do exist, they are not as specific or prevalent in the context of web applications, making XSS a more relevant concern in this sphere. Network congestion, on the other hand, relates to performance issues rather than security vulnerabilities.