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Medium

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

  • Disclosed: 25.03.2026
  • Updated: 11.10.2026 10:22

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.

Affected software

Click a technology to see all vulnerabilities affecting it.

PlatformPackageVulnerable versionsFixed in
npm package fastify < 5.8.3 5.8.3

References

CVSS score 6.1/10
CVSS vector
CVSS:3.1/AV:A/AC:H/PR:N/UI:N/S:C/C:H/I:N/A:N
Weakness (CWE)
CWE-348
Platform
npm
Package
fastify
Disclosed
25.03.2026
Updated
11.10.2026 10:22

Sources and licenses

OSV / GitHub Advisory Database - GHSA-444r-cwp2-x5xf - CC BY 4.0

Vulnerability history: fastify

All published vulnerabilities of this package (npm package), newest first. Shows whether this is a one-off slip or a package that needs watching.

All (16) in the archive
Total entries
16
First → latest
07.2018 09.2026
Without a fix
0
Exploited in attacks
0

Severity breakdown

  • High 8
  • Medium 7
  • Low 1

Disclosures per year

Severity:
  1. fastify vulnerable to request body replacement via an async validation result collision
    High · 8.1 CVE-2026-84504 < 5.12.2 5.12.2
  2. fastify vulnerable to authentication bypass via malformed URLs reaching encapsulated not-found handlers
    High · 7.5 CVE-2026-76169 >= 4.0.0, < 5.12.2 5.12.2
  3. fastify vulnerable to request validation bypass via skipped boolean false schemas
    High · 7.5 CVE-2026-84469 < 5.12.2 5.12.2
  4. fastify vulnerable to header validation bypass via incomplete schema case normalization
    High · 7.5 CVE-2026-84428 < 5.12.2 5.12.2
  5. fastify: request.protocol and request.host Spoofable via X-Forwarded-Proto/Host from Untrusted Connections this entry
    Medium · 6.1 CVE-2026-3635 < 5.8.3 5.8.3
  6. Fastify's Content-Type header tab character allows body validation bypass
    High · 7.5 CVE-2026-25223 < 5.7.2 5.7.2
  7. Fastify vulnerable to invalid content-type parsing, which could lead to validation bypass
    High · 7.5 CVE-2025-32442 >= 5.0.0, < 5.3.2, >= 4.29.0, < 4.29.1 5.3.2, 4.29.1
  8. fastify vulnerable to denial of service via malicious Content-Type
    High · 7.5 CVE-2022-39288 >= 4.0.0, < 4.8.1 4.8.1
  9. Denial of Service vulnerability with large JSON payloads in fastify
    High · 7.5 CVE-2018-3711 < 0.38.0 0.38.0

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