Vulnerability-Lookup

CVE-2026-3635 (GCVE-0-2026-3635)

Vulnerability from cvelistv5 – Published: 2026-03-23 13:53 – Updated: 2026-03-23 15:30

Title

Fastify request.protocol and request.host spoofable via X-Forwarded-Proto/Host from untrusted connections when trustProxy uses restrictive trust function

Summary

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.

Severity ?

6.1 (Medium)


                        
                          CVSS:3.1/AV:A/AC:H/PR:N/UI:N/S:C/C:H/I:N/A:N

CWE

CWE-348 - Use of less trusted source

Assigner

openjs

References

URL

Tags

	https://github.com/fastify/fastify/security/advis…
	https://www.cve.org/CVERecord?id=CVE-2026-3635
	https://cna.openjsf.org/security-advisories.html

Impacted products

	Vendor	Product	Version
	fastify	fastify	Affected: 0 , ≤ 5.8.2 (semver) Unaffected: 5.8.3 (semver)

Credits

LetaoZhao (TinkAnet) KaKa (climba03003) Matteo Collina Ulises Gascón

Show details on NVD website

JSON

To clipboard

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FKIE_CVE-2026-3635

Vulnerability from fkie_nvd - Published: 2026-03-23 14:16 - Updated: 2026-03-23 14:31

Severity ?

6.1 (Medium) - CVSS:3.1/AV:A/AC:H/PR:N/UI:N/S:C/C:H/I:N/A:N

Summary

References

	URL	Tags
	ce714d77-add3-4f53-aff5-83d477b104bb	https://cna.openjsf.org/security-advisories.html
	ce714d77-add3-4f53-aff5-83d477b104bb	https://github.com/fastify/fastify/security/advisories/GHSA-444r-cwp2-x5xf
	ce714d77-add3-4f53-aff5-83d477b104bb	https://www.cve.org/CVERecord?id=CVE-2026-3635

Impacted products

	Vendor	Product	Version

JSON

To clipboard

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  "cveTags": [],
  "descriptions": [
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      "lang": "en",
      "value": "Summary\nWhen trustProxy is configured with a restrictive trust function (e.g., a specific IP like trustProxy: \u002710.0.0.1\u0027, 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 \u2014 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.\n\nAffected Versions\nfastify \u003c= 5.8.2\n\nImpact\nApplications 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.\n\nWhen trustProxy: true (trust everything), both host and protocol trust all forwarded headers \u2014 this is expected behavior. The vulnerability only manifests with restrictive trust configurations."
    }
  ],
  "id": "CVE-2026-3635",
  "lastModified": "2026-03-23T14:31:37.267",
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          "confidentialityImpact": "HIGH",
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GHSA-444R-CWP2-X5XF

Vulnerability from github – Published: 2026-03-25 19:32 – Updated: 2026-03-25 19:32

Summary

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

Details

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.

Severity ?

6.1 (Medium)


                  
                    CVSS:3.1/AV:A/AC:H/PR:N/UI:N/S:C/C:H/I:N/A:N

Show details on source website

JSON

To clipboard

{
  "affected": [
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 5.8.2"
      },
      "package": {
        "ecosystem": "npm",
        "name": "fastify"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "5.8.3"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
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    "CVE-2026-3635"
  ],
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      "CWE-348"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-03-25T19:32:28Z",
    "nvd_published_at": "2026-03-23T14:16:34Z",
    "severity": "MODERATE"
  },
  "details": "## Summary\n\nWhen `trustProxy` is configured with a restrictive trust function (e.g., a specific IP like `trustProxy: \u002710.0.0.1\u0027`, 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 \u2014 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.\n\n## Affected Versions\n\nfastify \u003c= 5.8.2\n\n## Impact\n\nApplications 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.\n\nWhen `trustProxy: true` (trust everything), both `host` and `protocol` trust all forwarded headers \u2014 this is expected behavior. The vulnerability only manifests with restrictive trust configurations.",
  "id": "GHSA-444r-cwp2-x5xf",
  "modified": "2026-03-25T19:32:28Z",
  "published": "2026-03-25T19:32:28Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/fastify/fastify/security/advisories/GHSA-444r-cwp2-x5xf"
    },
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      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-3635"
    },
    {
      "type": "WEB",
      "url": "https://cna.openjsf.org/security-advisories.html"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/fastify/fastify"
    },
    {
      "type": "WEB",
      "url": "https://github.com/fastify/fastify/releases/tag/v5.8.3"
    },
    {
      "type": "WEB",
      "url": "https://www.cve.org/CVERecord?id=CVE-2026-3635"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:A/AC:H/PR:N/UI:N/S:C/C:H/I:N/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "fastify: request.protocol and request.host Spoofable via X-Forwarded-Proto/Host from Untrusted Connections"
}

Sightings

Author	Source	Type	Date

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

Detection rules are retrieved from Rulezet.

Action not permitted

CVE-2026-3635 (GCVE-0-2026-3635)

FKIE_CVE-2026-3635

GHSA-444R-CWP2-X5XF

Summary

Affected Versions

Impact

Tags

Sightings

Nomenclature