Content Security Policy (CSP) Header Generator
Generate hardened Content Security Policy Level 3 headers with presets for Next.js, WordPress, and zero-trust security.
Policy Directives
Navigation, Sandboxing & Ingestion
Generated Output
Content-Security-Policy: default-src 'self'; script-src 'self'; style-src 'self' 'unsafe-inline'; img-src 'self' data: https:; font-src 'self' data:; connect-src 'self'; object-src 'none'; frame-ancestors 'none'; base-uri 'self'; form-action 'self'; upgrade-insecure-requests;
Architectural Foundations of Content Security Policy (Level 3)
Content Security Policy (CSP) is a W3C declarative standard engineered to restrict the execution privileges of dynamic web applications. While CSP controls where scripts and styles can be fetched, multi-threaded applications requiring WebAssembly atomics must also configure process-level boundaries using our COOP & COEP isolation header checker. By restricting executable scripts, fonts, and embedded frames, CSP converts untrusted user input into inert runtime errors.
XSS Execution Neutralization
Stops reflected, stored, and DOM-based Cross-Site Scripting attacks by rejecting unauthorized inline script tags, dynamic `eval()` execution, and unvetted third-party JavaScript dependencies.
Clickjacking & Sandbox Defense
The `frame-ancestors` directive supersedes legacy `X-Frame-Options` headers to prevent UI redressing. For comprehensive iframe sandboxing, pair your policy with our Permissions-Policy header generator to restrict camera, microphone, and geolocation access across child frames.
Automated Insecurity Upgrades
Using `upgrade-insecure-requests`, user agents seamlessly rewrite legacy unencrypted HTTP resource URLs to HTTPS before sending network requests, eliminating mixed-content warnings.
Core Directives & Fallback Hierarchy Reference
CSP enforces a hierarchical fallback structure. If a specialized fetch directive is omitted from the policy, modern user agents fall back to the rules configured in default-src. When defining external endpoints inside connect-src, verify that those remote services also permit your domain by testing them in the CORS header preflight validator to ensure browser requests complete successfully:
| Directive | Governed Resources | Falls Back To default-src? | Recommended Strict Setting |
|---|---|---|---|
| default-src | Universal fallback for fetch directives | N/A (Root Directive) | 'self' or 'none' |
| script-src | External scripts and inline executable logic | Yes | 'self' + Nonce |
| style-src | External stylesheets and inline <style> blocks | Yes | 'self' 'unsafe-inline' |
| object-src | Plugins (<object>, <embed>, <applet>) | Yes | 'none' |
| frame-ancestors | Embedding contexts (<iframe>, <frame>) | No (Ignored by default-src) | 'none' or 'self' |
| base-uri | Document base URL manipulated via <base> tag | No (Ignored by default-src) | 'self' |
Enterprise Web Server Configuration Examples
To enforce your policy across all connected clients, attach the header in your edge reverse proxy or web application gateway. Below are production configurations for Nginx and Apache:
Nginx Reverse Proxy
# /etc/nginx/conf.d/security-headers.conf
server {
listen 443 ssl http2;
server_name example.com;
# Add CSP Header to all HTTP responses
add_header Content-Security-Policy "default-src 'self'; script-src 'self'; style-src 'self' 'unsafe-inline'; object-src 'none'; frame-ancestors 'none'; upgrade-insecure-requests;" always;
}Apache (.htaccess / VirtualHost)
# Apache HTTP Server Configuration
<IfModule mod_headers.c>
Header set Content-Security-Policy \
"default-src 'self'; \
script-src 'self'; \
style-src 'self' 'unsafe-inline'; \
object-src 'none'; \
frame-ancestors 'none'; \
upgrade-insecure-requests;"
</IfModule>Safe Rollout: Utilizing Report-Only Mode Without Breaking Production
Deploying an unvetted Content Security Policy directly into a live production system can inadvertently break third-party analytics, payment gateways, and CSS frameworks. A staged deployment strategy mitigates this risk:
Safe Rollout Best Practices
- • Start with Content-Security-Policy-Report-Only: Violations will be posted to your logging endpoint while all scripts, styles, and assets continue rendering normally for end users.
- • Aggregate Violation Logs: Ingest reports into your observability stack (e.g. Datadog, Sentry, or an internal collector) to identify missing CDN origins.
- • Transition to Nonces: Swap
'unsafe-inline'with dynamically generated server-side cryptographic nonces for script tags.
High-Risk Policy Antipatterns
- • Wildcard Origins (
*orhttps:): Allows attackers to host and execute malicious scripts from arbitrary domains or cloud storage buckets. - • Omitting object-src 'none': Leaves the browser vulnerable to plugins that do not respect script sandboxing.
- • Overreliance on HTML <meta> Tags: Certain critical security directives like
frame-ancestorsare silently discarded by browsers when parsed via HTML meta tags.
Frequently Asked Questions (FAQ)
What is a Content Security Policy (CSP) and why is it essential?
A Content Security Policy (CSP) is an HTTP response header that restricts the resources (JavaScript, CSS, Images, Frames, Fonts) the browser is allowed to load for a given document. It serves as an essential defense-in-depth security layer that drastically reduces the attack surface for Cross-Site Scripting (XSS), data injection, and clickjacking attacks.
Can I enforce a Content Security Policy via an HTML <meta> tag?
Yes, standard CSP policies can be defined using <meta http-equiv="Content-Security-Policy" content="...">. However, certain directives—specifically frame-ancestors, report-uri, and report-to—are strictly ignored inside meta tags by modern browsers and require direct HTTP response header injection.
What is the difference between Content-Security-Policy and Content-Security-Policy-Report-Only?
Content-Security-Policy actively blocks unauthorized resource requests from executing, whereas Content-Security-Policy-Report-Only allows resources to load normally while sending JSON telemetry violation reports to a designated URI endpoint, allowing teams to test strict policies without breaking live features.
Why is 'unsafe-inline' dangerous for script-src?
'unsafe-inline' allows inline script tags (<script>alert(1)</script>) and inline event handlers (onclick=...) to execute without validation, which negates the primary anti-XSS protection that CSP is engineered to provide. Nonce-based or cryptographic hash configurations should always be used instead.
What does object-src 'none' protect against?
Setting object-src 'none' blocks legacy browser plugins like Flash, Java Applets, and Silverlight embedded via <object>, <embed>, or <applet> tags. Because modern HTML5 applications do not require plugins, setting object-src 'none' eliminates plugin-based memory vulnerabilities completely.
How does frame-ancestors prevent Clickjacking attacks?
The frame-ancestors directive dictates whether an external website is permitted to embed your webpage inside an <iframe>, <frame>, or <object>. Setting it to 'none' or 'self' supersedes the legacy X-Frame-Options HTTP response header and defends against UI-redressing and clickjacking exploits.
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