CVE-2026-3635

## Summary When `trustProxy` is configured with a restrictive trust function (e.g., a specific IP like `trustProxy: '10.0.0.1'`, a subnet, a hop count, or a custom function), the `request.protocol` and `request.host` getters read `X-Forwarded-Proto` and `X-Forwarded-Host` headers from any connection — including connections from untrusted IPs. This allows an attacker connecting directly to Fastify (bypassing the proxy) to spoof both the protocol and host seen by the application. ## Affected Versions fastify <= 5.8.2 ## Impact Applications using `request.protocol` or `request.host` for security decisions (HTTPS enforcement, secure cookie flags, CSRF origin checks, URL construction, host-based routing) are affected when `trustProxy` is configured with a restrictive trust function. When `trustProxy: true` (trust everything), both `host` and `protocol` trust all forwarded headers — this is expected behavior. The vulnerability only manifests with restrictive trust configurations.