{
  "affected": [
    {
      "ranges": [
        {
          "database_specific": {
            "cpe": "cpe:2.3:a:fastify:fastify:*:*:*:*:*:node.js:*:*",
            "extracted_events": [
              {
                "introduced": "0"
              },
              {
                "last_affected": "5.8.2"
              },
              {
                "fixed": "5.8.3"
              }
            ],
            "source": [
              "AFFECTED_FIELD",
              "CPE_RANGE"
            ]
          },
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "a3e77ce171516e95f0c28ce60b9e5228a4c42fe4"
            }
          ],
          "repo": "https://github.com/fastify/fastify",
          "type": "GIT"
        }
      ]
    }
  ],
  "aliases": [
    "GHSA-444r-cwp2-x5xf"
  ],
  "database_specific": {
    "cna_assigner": "openjs",
    "cwe_ids": [
      "CWE-348"
    ],
    "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/3xxx/CVE-2026-3635.json"
  },
  "details": "Summary\nWhen 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.\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 — this is expected behavior. The vulnerability only manifests with restrictive trust configurations.",
  "id": "CVE-2026-3635",
  "modified": "2026-07-08T05:36:07.381144719Z",
  "published": "2026-03-23T13:53:00.386Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://www.cve.org/CVERecord?id=CVE-2026-3635"
    },
    {
      "type": "ADVISORY",
      "url": "https://cna.openjsf.org/security-advisories.html"
    },
    {
      "type": "ADVISORY",
      "url": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/3xxx/CVE-2026-3635.json"
    },
    {
      "type": "ADVISORY",
      "url": "https://github.com/fastify/fastify/security/advisories/GHSA-444r-cwp2-x5xf"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-3635"
    }
  ],
  "schema_version": "1.7.5",
  "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 when trustProxy uses restrictive trust function"
}