Allowlists decay with the front end
A location-based policy tends to accumulate analytics, widgets, tag managers, and content hosts. One risky script endpoint on any allowed origin can weaken the whole boundary, while reviewers struggle to understand why each domain remains trusted.
A strict CSP builds trust around a cryptographic nonce or hash. The browser executes code explicitly approved by the response, so an injected script on the same origin still lacks authority to run.
Choose nonces or hashes deliberately
A nonce must be unpredictable and unique for every response, then copied into both the CSP header and approved script elements. Static pages often fit hashes better: the policy can stay identical until the script changes, when the hash must be recalculated.
Add object-src 'none' and base-uri 'none', then model frames, API connections, images, and workers explicitly. Avoid broad fallbacks that quietly reopen the surface you intended to close.
- Deploy Content-Security-Policy-Report-Only before enforcing.
- Remove inline handlers and eval-style execution.
- Never reuse a predictable nonce across responses.
- Review violation reports after meaningful front-end changes.
CSP is a second line, not a pardon
Context-aware output encoding and safe DOM APIs remain the foundation. CSP reduces the impact of mistakes; it does not make unsafe rendering acceptable.
Validate the policy with controlled injection attempts across representative routes. Silence in the browser console is not proof—the real test is that injected code cannot execute while legitimate features continue to work.