Fixing Content Security Policy without guessing

Guessing a CSP from a random GitHub gist is how you break checkout on Friday. The public site either restricts browser content sources with a CSP header or it does not. Your fix should start from the URLs and hosts you actually serve—not from a policy that belonged to someone else's stack.

SlaySlop's CSP check "Checks whether browser content sources are restricted by a CSP header." This post is about closing that gap without inventing allowlists you cannot defend.

Outcome you want

After the fix, launch URLs send an enforcing CSP that matches real script, style, and frame needs closely enough to restrict what should be restricted, Console errors stay manageable, and a follow-up scan no longer flags the same CSP miss on those routes. HSTS and Frame protection get a glance in the same change window so the Security story is coherent for readers and crawlers alike.

Boundaries before you edit

CSP is one Security signal. It is not the XSS check. It is not legal advice. SlaySlop is read-only and will not push edge config. Only change hosts you own, manage, or have permission to test. Report-Only is a tool for learning breakages; do not stop there if the finding was about missing restriction.

Thin pages and thin policies share a failure mode: they look complete from far away. Editors notice empty meta; browsers notice empty security headers. Fix both classes with evidence.

Fix path without guessing

1. Read the evidence URL

Open the pages SlaySlop attached. Confirm what the response actually sends.

curl -sI "https://www.example.com/checkout" | rg -i 'HTTP/|content-security-policy'

2. Inventory hosts from a real load

In a permissioned browser session, note script and frame origins the page needs. Do not invent https://cdn.example.com because a tutorial used it.

Host inventory for /checkout
scripts:
frames:
connect:
fonts:
images:

3. Draft the smallest restricting policy that matches inventory

Prefer 'self' plus explicit hosts. Keep 'unsafe-inline' / 'unsafe-eval' off the default path unless you have a dated exception and an owner. Set object-src 'none' unless you have a concrete plugin need. Example shape only:

Content-Security-Policy: default-src 'self'; script-src 'self' https://cdn.example.com https://pay.vendor.example; object-src 'none'; base-uri 'self'; frame-ancestors 'self'

Your hosts will differ. The point is mapping, not copying.

4. Ship where traffic goes

CDN and app both love to own headers. Pick one source of truth. Apply to apex and www if both serve. Do not leave checkout on a bare origin.

5. Verify with humans and the scanner

Click the primary paths. Watch Console errors and Failed requests. Then rescan in SlaySlop so the CSP row updates against the live surface. Fix prompts help turn evidence into a paste-ready editor prompt; they do not replace the rescan.

Pitfalls

Pasting a strict policy that blocks your own tag manager, then deleting CSP in a panic. Enforcing on staging only. Forgetting Report-Only was never flipped. Documenting the policy for SEO copy ("we use CSP") while the header stays absent—crawlers may index the claim; browsers still see the gap.

What good evidence looks like after the fix

Same URL family as the finding. Header dump showing enforcing CSP. Short note on allowlisted hosts. Sibling HSTS present or ticketed. Scan ID where the CSP finding cleared. That package reads cleanly to engineers and to anyone maintaining the public help center wording later.

I also keep a one-line summary for non-engineers: "Browsers on /checkout now only load scripts from our CDN and the payment vendor we named." If I cannot say that sentence, the policy is still too vague to hand to a client.

Editorial hygiene while you harden

If your site claims security practices on a trust or security page, make sure the live header matches the prose. Answer engines and careful buyers both notice mismatches between marketing copy and response headers. CSP will not write your meta description, but a false CSP claim in HTML is worse than a quiet Security row you are actively fixing.

Rollback rule

If a policy breaks payments, roll back to the last known good header—or temporarily widen only the blocking directive—then fix the allowlist with evidence. Do not leave production without CSP overnight because a vendor SDK path changed.

Related next step

After CSP is clean on launch URLs, keep HSTS and Frame protection in the same Security pass, and watch Console errors for fallout. Soft link: Content Security Policy and checks.