Fastify's Missing End Anchor in "subtypeNameReg" Allows Malformed Content-Types to Pass Validation

{
  "id": "5831f21a5e05b3faac48aeca2b1006f8cd7b69e33b554ff8fa1004363d754d97",
  "url": "https://osv.dev/vulnerability/CVE-2026-3419",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "Fastify's Missing End Anchor in \"subtypeNameReg\" Allows Malformed Content-Types to Pass Validation",
    "summary": "Fastify incorrectly accepts malformed `Content-Type` headers containing trailing characters after the subtype token, in violation of RFC 9110 §8.3.1(https://httpwg.org/specs/rfc9110.html#field.content-type). For example, a request sent with Content-Type: application/json garbage passes validation and is processed normally, rather than being rejected with 415 Unsupported Media Type. When regex-based content-type parsers are in use (a documented Fastify feature), the malformed value is matched against registered parsers using the full string including the trailing garbage. This means a request with an invalid content-type may be routed to and processed by a parser it should never have reached. Impact: An attacker can send requests with RFC-invalid Content-Type headers that bypass validity checks, reach content-type parser matching, and be processed by the server. Requests that should be rejected at the validation stage are instead handled as if the content-type were valid. Workarounds: Deploy a WAF rule to protect against this Fix: The fix is available starting with v5.8.1.",
    "evidence": "osv:CVE-2026-3419",
    "products": [],
    "severity": "medium",
    "structured": {
      "id": "CVE-2026-3419",
      "aliases": [
        "CVE-2026-3419",
        "GHSA-573f-x89g-hqp9"
      ],
      "metrics": [
        {
          "type": "CVSS_V3",
          "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://github.com/fastify/fastify",
              "type": "GIT",
              "events": [
                {
                  "introduced": "e1e4fe75910c36e1b9ebb87026ca16c053a9c1f2"
                },
                {
                  "fixed": "073ff8132f350aaa53935231019499e983cb9794"
                },
                {
                  "fixed": "67f6c9b32cb3623d3c9470cc17ed830dd2f083d7"
                }
              ],
              "database_specific": {
                "extracted_events": [
                  {
                    "cpe": "cpe:2.3:a:fastify:fastify:*:*:*:*:*:node.js:*:*",
                    "range": [
                      {
                        "introduced": "5.7.2"
                      },
                      {
                        "fixed": "5.8.1"
                      }
                    ],
                    "source": "CPE_RANGE"
                  },
                  {
                    "range": [
                      {
                        "fixed": "67f6c9b32cb3623d3c9470cc17ed830dd2f083d7"
                      }
                    ],
                    "source": "REFERENCES_COMMIT"
                  }
                ]
              }
            }
          ],
          "versions": [
            "v5.8.0",
            "v5.7.4",
            "v5.7.3",
            "v5.7.2"
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-3419.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:31.051888989Z",
      "provider": "osv",
      "references": [
        "https://httpwg.org/specs/rfc9110.html#field.content-type",
        "https://www.cve.org/CVERecord?id=CVE-2026-3419",
        "https://cna.openjsf.org/security-advisories.html",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/3xxx/CVE-2026-3419.json",
        "https://github.com/advisories/GHSA-573f-x89g-hqp9",
        "https://github.com/fastify/fastify/security/advisories/GHSA-573f-x89g-hqp9",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-3419",
        "https://github.com/fastify/fastify/commit/67f6c9b32cb3623d3c9470cc17ed830dd2f083d7"
      ],
      "provider_metadata": {
        "cwe_ids": [
          "CWE-185"
        ],
        "cna_assigner": "openjs",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/3xxx/CVE-2026-3419.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-3419",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 498002,
  "published_at": "2026-03-06T17:50:58.714+00:00"
}