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RFC 9110 / W3C CSP3
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Content Security Policy & CORS Architect
Visually construct hardened HTTP security headers, generate WebCrypto nonces, compute SHA-256 script hashes, and audit policies for dangerous XSS injection vectors.
Directives & Source Allowlist
🛡️ Policy Vulnerability Assessment
SAFE RATING: 90/100
Cryptographic Nonce Entropy & Preflight Latency Architecture
Modern web applications secure dynamic scripts without allowing raw inline execution through cryptographic nonces and SHA-256 hashes generated by CSPRNG hardware entropy sources:
1. Cryptographic Nonce Entropy Formulation:
H = log_2(64^N) = N imes 6 ext{ bits} quad ( ext{For } 16 ext{ bytes / } 128 ext{ bits entropy, collision probability } P < 10^{-18})
2. Subresource Hash Ingestion:
ext{Digest} = ext{Base64}( ext{SHA-256}( ext{ScriptPayload})) quad ( ext{Bitwise exact match across whitespace})
3. CORS Preflight RTT Latency Optimization:
Delta T_{ ext{saved}} = N_{ ext{subsequent requests}} imes ext{RTT} quad ( ext{Eliminates round-trip OPTIONS preflight overhead})
5 Fatal Traps in Content Security Policy & CORS Configuration
1. The 'unsafe-inline' and 'unsafe-eval' Script Compromise Trap
Adding
'unsafe-inline' to script-src completely disables CSP protection against Stored and Reflected XSS. If an attacker injects a script tag or inline event handler (onload, onerror), the browser executes it without validation. Production systems should strictly use random per-request nonces or SHA-256 hashes.
2. The Wildcard Origin with Credentials Exploit ('*' with Allow-Credentials: true)
W3C and RFC 9110 strictly forbid returning
Access-Control-Allow-Origin: * alongside Access-Control-Allow-Credentials: true. When this happens, browsers drop the response entirely. Naive backends often "fix" this by reflecting the incoming request's Origin header, effectively allowing any malicious website on the internet to read authenticated user cookies.
3. Relying on Legacy X-Frame-Options Instead of frame-ancestors
Legacy
X-Frame-Options: SAMEORIGIN does not support multiple allowed parent domains and is ignored by modern browsers when a CSP is present. Omitting frame-ancestors 'self' from your CSP allows malicious sites to embed your pages inside transparent iframes, executing Clickjacking and UI redress attacks against authenticated sessions.
4. Broad CDN Allowlisting & JSONP Bypass Endpoints
Allowlisting entire shared CDNs like
https://cdnjs.cloudflare.com or https://cdn.jsdelivr.net creates easy CSP bypasses. Attackers can find outdated AngularJS versions or vulnerable JSONP endpoints hosted on the same CDN to execute arbitrary JavaScript within your domain origin. Always pin sub-paths or use SRI hashes.
5. The Missing base-uri Injection Vulnerability
Omitting the
base-uri 'self' directive allows attackers who discover HTML injection vulnerabilities to insert a <base href="https://evil.com"> tag. This rewrites all relative script paths on your page to load from the attacker's server, bypassing your domain allowlists and executing hostile code.
Frequently Asked Technical Questions
What is the difference between CSP and CORS?+
Content Security Policy (CSP) is an HTTP response header that restricts the resources (scripts, styles, images, iframes) the browser is allowed to load for a page, preventing Cross-Site Scripting (XSS) and clickjacking. Cross-Origin Resource Sharing (CORS) manages which external origins are allowed to read responses from your API via XMLHttpRequest or Fetch.
Why is unsafe-inline dangerous in script-src?+
Specifying unsafe-inline allows any inline script tag or inline event handler to execute without verification. If an attacker injects user input into the DOM, the browser executes it immediately. Using cryptographic nonces or SHA-256 hashes ensures only approved scripts run.
How does frame-ancestors protect against clickjacking?+
The frame-ancestors directive obsoletes the legacy X-Frame-Options header. Setting frame-ancestors self or none stops malicious third-party websites from framing your application inside transparent iframes to trick authenticated users into clicking unauthorized actions.
What is the maximum preflight cache duration for Access-Control-Max-Age?+
The Access-Control-Max-Age header tells the browser how many seconds to cache the OPTIONS preflight response. While the specification allows arbitrary values, modern browsers enforce internal caps: Chromium-based browsers cap preflights at 7,200 seconds (2 hours), while Firefox allows up to 86,400 seconds (24 hours).
Can a strict Content Security Policy break third-party tag managers or analytics?+
Yes. If a tag manager dynamically injects remote scripts or creates inline snippets without matching hashes or nonces, a strict CSP will block them. Production deployments must allowlist the tag manager domains and configure server-side nonce propagation to dynamically generated tags.
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