What is CVE-2026-3635?

CVE-2026-3635 is a medium-severity vulnerability in Fastify, classified under CWE-348. CVSS score: 6.1/10. Published 2026-03-23.

How severe is CVE-2026-3635?

Medium severity. CVSS v3 base score is 6.1 out of 10.

Vulnerability in Fastify

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 an…

EPSS: 0.000 (1.9th percentile) — read the EPSS interpretation.

CVSS v3 metric

CVSS v3 base score 6.1 (Medium). Vector: CVSS:3.1/AV:A/AC:H/PR:N/UI:N/S:C/C:H/I:N/A:N.

Affected products

Fastify — versions 0, 5.8.3

Weakness classification (CWE)

CWE-348

References

github.com/fastify/fastify/security/advisories/GHSA-444r-cwp2-x5xf
www.cve.org/CVERecord
cna.openjsf.org/security-advisories.html

Frequently asked questions

What is CVE-2026-3635?: CVE-2026-3635 is a medium-severity vulnerability in Fastify, classified under CWE-348. CVSS score: 6.1/10. Published 2026-03-23.
How severe is CVE-2026-3635?: Medium severity. CVSS v3 base score is 6.1 out of 10.