GHSA-573F-X89G-HQP9

Vulnerability from github – Published: 2026-03-05 21:29 – Updated: 2026-03-06 22:44
VLAI?
Summary
Fastify's Missing End Anchor in "subtypeNameReg" Allows Malformed Content-Types to Pass Validation
Details

Description

Fastify incorrectly accepts malformed Content-Type headers containing trailing characters after the subtype token, in violation of RFC 9110 §8.3.1. 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.

Severity ?
5.3 (Medium)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
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{
  "affected": [
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 5.8.0"
      },
      "package": {
        "ecosystem": "npm",
        "name": "fastify"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "5.7.2"
            },
            {
              "fixed": "5.8.1"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-3419"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-185"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-03-05T21:29:54Z",
    "nvd_published_at": "2026-03-06T18:16:22Z",
    "severity": "MODERATE"
  },
  "details": "# Description\n\nFastify incorrectly accepts malformed `Content-Type` headers containing trailing characters after the subtype token, in violation of [RFC 9110 \u00a78.3.1](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`.\n\nWhen 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.\n\n## Impact\n\nAn 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.\n\n## Workarounds\n\nDeploy a WAF rule to protect against this\n\n## Fix\n\nThe fix is available starting with v5.8.1.",
  "id": "GHSA-573f-x89g-hqp9",
  "modified": "2026-03-06T22:44:34Z",
  "published": "2026-03-05T21:29:54Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/fastify/fastify/security/advisories/GHSA-573f-x89g-hqp9"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-3419"
    },
    {
      "type": "WEB",
      "url": "https://github.com/fastify/fastify/commit/67f6c9b32cb3623d3c9470cc17ed830dd2f083d7"
    },
    {
      "type": "WEB",
      "url": "https://cna.openjsf.org/security-advisories.html"
    },
    {
      "type": "ADVISORY",
      "url": "https://github.com/advisories/GHSA-573f-x89g-hqp9"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/fastify/fastify"
    },
    {
      "type": "WEB",
      "url": "https://httpwg.org/specs/rfc9110.html#field.content-type"
    },
    {
      "type": "WEB",
      "url": "https://www.cve.org/CVERecord?id=CVE-2026-3419"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "Fastify\u0027s Missing End Anchor in \"subtypeNameReg\" Allows Malformed Content-Types to Pass Validation"
}


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