EUVD-2026-14431
GHSA-444r-cwp2-x5xf
CVSS Vector
CVSS:3.1/AV:A/AC:H/PR:N/UI:N/S:C/C:H/I:N/A:N
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4Tags
Description
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.
Analysis
Fastify versions 5.8.2 and earlier contain a header spoofing vulnerability in the trustProxy implementation where the request.protocol and request.host getters incorrectly trust X-Forwarded-Proto and X-Forwarded-Host headers even from untrusted connections when a restrictive trust function is configured. An attacker who can connect directly to a Fastify instance (bypassing the intended proxy) can spoof protocol and host values, potentially bypassing HTTPS enforcement, manipulating secure cookie behavior, and defeating CSRF origin checks. …
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Remediation
Within 30 days: Identify affected systems and apply vendor patches as part of regular patch cycle. Monitor vendor channels for patch availability.
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