Cross-Site Scripting (XSS) | Playful Sparkle

Cross-Site Scripting (XSS) is a code injection vulnerability where an attacker executes malicious scripts within a victim’s browser by injecting code into a legitimate web application.

XSS remains one of the most prevalent threats in web development. Attackers utilize it to hijack user sessions, scrape sensitive data, or perform unauthorized actions on behalf of the user. Professional defense requires a “Defense in Depth” strategy: combining strict Input Validation, context-aware Output Encoding, and the implementation of a robust Content Security Policy (CSP) to restrict the execution of unauthorized scripts.

Frequently Asked Questions

Stored XSS occurs when the malicious script is permanently saved on the target server (e.g., in a database via a comment field). Reflected XSS occurs when the script is part of a request (usually a URL parameter) and is immediately “reflected” back to the user without being stored.

A CSP is an HTTP response header that tells the browser which sources of content (scripts, styles, images) are trusted. By disallowing “inline scripts” and restricted execution to known domains, a CSP can neutralize XSS attacks even if an injection vulnerability exists in the code.

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Frequently Asked Questions

What is the difference between Stored and Reflected XSS?

How does a Content Security Policy (CSP) mitigate XSS?

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