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Content Security Policy: Protecting Against XSS

Implement CSP to prevent XSS attacks. Learn directives, reporting, and deployment strategies.

B
Bootspring Team
Engineering
February 27, 2026
3 min read

Content Security Policy (CSP) is a powerful defense against XSS and injection attacks.

Basic CSP Header#

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Common Directives#

default-src - Fallback for other directives script-src - JavaScript sources style-src - CSS sources img-src - Image sources font-src - Font sources connect-src - XHR, WebSocket, fetch sources frame-src - iframe sources object-src - plugins (Flash, etc.) base-uri - <base> tag restrictions form-action - Form submission targets frame-ancestors - Who can embed this page

Practical CSP Examples#

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Nonce-Based CSP#

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Hash-Based CSP#

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Next.js CSP#

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CSP Reporting#

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Deployment Strategy#

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Common Issues#

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CSP significantly reduces XSS risk when implemented properly.

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