Real-World Attack Scenarios

Examining real-world attack scenarios illustrates how technical vulnerabilities translate into actual compromises. Consider an online banking application with an XSS vulnerability in the transaction history search feature. An attacker could craft a malicious link that, when clicked by a logged-in user, executes JavaScript to initiate a money transfer. The script could read the user's account balance, determine the maximum transferable amount, submit a transfer form to the attacker's account, and then redirect the user to a benign page, all within seconds.

Another scenario involves a corporate collaboration platform with stored XSS in document comments. An attacker could inject a payload that silently exfiltrates sensitive documents whenever colleagues view the infected comment. The script could enumerate accessible documents, download them in the background, and transmit them to an external server. Such attacks might operate for months before detection, compromising vast amounts of corporate data.

Understanding how XSS attacks work at a technical level empowers developers to build better defenses. The key insight is that XSS fundamentally exploits the browser's inability to distinguish between legitimate and malicious code when both come from trusted sources. This understanding drives security best practices: never trust user input, always encode output appropriately for its context, implement defense-in-depth with CSP and other security headers, and regularly test applications for XSS vulnerabilities. As browsers and web technologies evolve, new attack vectors may emerge, but the fundamental principle remains: prevent untrusted data from being interpreted as code.