Xss

Content Security Policy: The Complete Guide for 2026 Content Security Policy, usually called CSP, is one of the most effective browser-side defenses against cross-site scripting, malicious third-party script execution, data injection, and a wide range of content loading abuses. When configured well, CSP reduces the damage an attacker can do even if some unsafe markup or script reaches the page. CSP is not a replacement for output encoding, input validation, secure templating, sandboxing, dependency review, or HTTP-only cookies. It is a powerful second line of defense. It tells the browser which resources are allowed to load, which scripts may execute, where forms may submit, whether the page may be framed, and where violations should be reported. ...

Content Security Policy has a reputation problem. A lot of teams either treat CSP like a magic anti-XSS shield, or they avoid it because they assume it will break everything. Both takes are wrong. CSP is powerful, but it’s also easy to misuse in ways that give you a nice-looking header and very little real protection. I’ve seen plenty of production policies that look serious because they’re long, but collapse the moment an inline script sneaks in or a third-party script gets too much trust. ...