GHSA-444r-cwp2-x5xf

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GHSA-444r-cwp2-x5xf

Summary: fastify: request.protocol and request.host Spoofable via X-Forwarded-Proto/Host from Untrusted Connections

Details: ## 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.

References: https://github.com/fastify/fastify/security/advisories/GHSA-444r-cwp2-x5xf, https://nvd.nist.gov/vuln/detail/CVE-2026-3635, https://cna.openjsf.org/security-advisories.html, https://github.com/fastify/fastify, https://github.com/fastify/fastify/releases/tag/v5.8.3, https://www.cve.org/CVERecord?id=CVE-2026-3635