CORS for Fastly
medium4 checks
CORS decides which origins may read your API responses. A wildcard turns an authenticated API into a public one.
What Fastly must have
- Access-Control-Allow-Origin limited to known origins
- No wildcard combined with credentials
- No reflection of arbitrary Origin headers
- Preflight responses only allow the methods actually used
How to fix it
- 1Replace wildcards with an explicit allowlist
- 2Validate Origin before echoing it and reject unknown origins early
Fastly context
Edge cloud and CDN with VCL configuration.
Review VCL for cache poisoning and ensure the origin only trusts Fastly IPs.