You are testing a dynamic website for vulnerabilities and input a test string that triggers a pop-up saying 'This is a test.' What vulnerability does this indicate?

• A. Your website is vulnerable to SQL injection
• B. Your website is vulnerable to CSS
• C. Your website is vulnerable to web bugs
• D. Your website is not vulnerable

Answer: (B)

The test is showing a client-side code execution opportunity through a CSS context. When user input can be placed into a style context and reflected in the page without proper sanitization, some browsers (notably older ones) could evaluate CSS that contains executable code, such as the infamous CSS expression construct. If an attacker can inject such CSS, the browser may run JavaScript embedded in the style rules, which would produce a pop-up like the one you saw. This indicates a CSS injection vulnerability, where untrusted input is trusted enough to influence CSS in a way that triggers script execution.

This isn’t about SQL queries or database problems (that would be SQL injection), nor is it the typical web bug tracking scenario. It’s specifically a CSS-based code execution risk caused by unsafe reflection of input into styling. To fix it, sanitize all user input, avoid inserting raw input into style attributes or style blocks, and consider stronger defenses like a strict content security policy and avoiding deprecated CSS features that can execute code.