Browser security headers

Security headers tell a browser which capabilities to allow.

• Content-Security-Policy restricts where scripts, styles, images, and other resources may load from.
• X-Content-Type-Options: nosniff tells the browser to respect declared content types.
• Referrer-Policy limits referrer information sent to other sites.
• Permissions-Policy controls selected browser features.
• frame-ancestors inside CSP controls which pages may embed yours.

A strict policy can break an existing site, so deploy carefully. Start by inventorying required sources. CSP can run in report-only mode while you observe violations.

Headers reduce risk but do not repair unsafe application code. You still need output escaping, input validation, secure authentication, and current dependencies.

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