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.
INFO
Published Date :
2026-03-23T13:53:00.386Z
Last Modified :
2026-03-23T15:30:10.526Z
Source :
openjs
AFFECTED PRODUCTS
The following products are affected by CVE-2026-3635 vulnerability.
| Vendors | Products |
|---|---|
| Fastify |
|
REFERENCES
Here, you will find a curated list of external links that provide in-depth information to CVE-2026-3635.
