The Trust Model That XSS Exploits

Web security operates on several trust boundaries, and XSS attacks specifically exploit the trust relationship between users, browsers, and websites. Users trust websites to deliver safe content, browsers trust properly formatted HTML and JavaScript from these websites, and websites trust authenticated users to perform certain actions. XSS attacks violate these trust boundaries by injecting malicious content that appears to come from a trusted source. When a user visits a compromised page, their browser sees scripts coming from a trusted domain and executes them without question.

This exploitation of trust makes XSS particularly dangerous in environments where users have elevated privileges. An XSS vulnerability in an admin panel could allow attackers to perform administrative actions, while XSS in a banking application could enable unauthorized transfers. The same-origin policy, a fundamental browser security mechanism, actually works against users here – since the malicious script executes in the context of the vulnerable website, it has access to all resources from that origin, including cookies, local storage, and the ability to make authenticated requests.