CVE-2026-3635Fastify request.protocol and request.host spoofable via X-Forwarded-Proto/Host from untrusted connections when trustProxy uses restrictive trust function
- 6.1MediumCVSS base score
- 0.15%Exploitation in 30 daysEPSS · top 95% of all CVEs
- NoKnown exploitednot in CISA's KEV catalog
- NonePublic exploitsnone known yet
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.
Timeline
ID reserved
By openjs
- 17 days later
· 17 days later
Published
Changes after publication (a new score, a public exploit, EPSS crossing 1, 10 or 50 %, leaving KEV) are kept since November 2026; earlier ones are not known.
Scores
| Scored by | CVSS | Score | Vector |
|---|---|---|---|
| openjsCNA (assigner) | 3.1 | Medium6.1 | CVSS:3.1/AV:A/AC:H/PR:N/UI:N/S:C/C:H/I:N/A:N |
| NVDNVD · Analyzed | 3.1 | Medium6.1 | CVSS:3.1/AV:A/AC:H/PR:N/UI:N/S:C/C:H/I:N/A:N |
- EPSS (exploitation in 30 days)
- 0.15% · top 95% of all CVEs (13 Nov 2026)
- CISA SSVC
- Exploitation: none · Automatable: no · Technical impact: partial
The list uses the assigner's score when there is one, then CISA's, then NVD's: Medium 6.1.
Affected products
Affected packages
From reviewed advisories of the GitHub Advisory Database.
- npmfastifyGHSA-444r-cwp2-x5xf (opens in a new tab)
References
Sources
The same CVE in the primary databases and aggregators, to check against.
- CVE.org record (opens in a new tab)
- CVE List JSON (GitHub) (opens in a new tab)
- NVD (opens in a new tab)
- FIRST EPSS (opens in a new tab)
- EUVD EUVD-2026-14431 (opens in a new tab)
- OSV.dev (opens in a new tab)
- GitHub Advisory GHSA-444r-cwp2-x5xf (opens in a new tab)
- CIRCL Vulnerability-Lookup (opens in a new tab)
Badge for a README or a ticket
[](https://cveledger.app/cve/CVE-2026-3635)Record last updated .