CVE-2026-3419 (GCVE-0-2026-3419)

Vulnerability from cvelistv5 – Published: 2026-03-06 17:50 – Updated: 2026-03-06 17:54
VLAI?
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.
Severity ?
5.3 (Medium)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
CWE
  • CWE-185 - Incorrect Regular Expression
Assigner
References
Impacted products
Vendor Product Version
fastify fastify Affected: 5.7.2 , < 5.8.1 (semver)
Unaffected: 5.8.1 (semver)
Create a notification for this product.
Credits
Saad FELLAHI James Sumners Matteo Collina Ulises Gascón
Show details on NVD website
To clipboard 

{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "packageURL": "pkg:npm/fastify",
          "product": "fastify",
          "vendor": "fastify",
          "versions": [
            {
              "lessThan": "5.8.1",
              "status": "affected",
              "version": "5.7.2",
              "versionType": "semver"
            },
            {
              "status": "unaffected",
              "version": "5.8.1",
              "versionType": "semver"
            }
          ]
        }
      ],
      "credits": [
        {
          "lang": "en",
          "type": "reporter",
          "value": "Saad FELLAHI"
        },
        {
          "lang": "en",
          "type": "remediation developer",
          "value": "James Sumners"
        },
        {
          "lang": "en",
          "type": "coordinator",
          "value": "Matteo Collina"
        },
        {
          "lang": "en",
          "type": "remediation reviewer",
          "value": "Ulises Gasc\u00f3n"
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "supportingMedia": [
            {
              "base64": false,
              "type": "text/html",
              "value": "Fastify 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\nImpact:\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\nWorkarounds:\nDeploy a WAF rule to protect against this\n\nFix:\n\nThe fix is available starting with v5.8.1."
            }
          ],
          "value": "Fastify 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\nImpact:\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\nWorkarounds:\nDeploy a WAF rule to protect against this\n\nFix:\n\nThe fix is available starting with v5.8.1."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "baseScore": 5.3,
            "baseSeverity": "MEDIUM",
            "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N",
            "version": "3.1"
          },
          "format": "CVSS",
          "scenarios": [
            {
              "lang": "en",
              "value": "GENERAL"
            }
          ]
        }
      ],
      "problemTypes": [
        {
          "descriptions": [
            {
              "cweId": "CWE-185",
              "description": "CWE-185: Incorrect Regular Expression",
              "lang": "en",
              "type": "CWE"
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-03-06T17:54:33.542Z",
        "orgId": "ce714d77-add3-4f53-aff5-83d477b104bb",
        "shortName": "openjs"
      },
      "references": [
        {
          "url": "https://github.com/fastify/fastify/security/advisories/GHSA-573f-x89g-hqp9"
        },
        {
          "url": "https://github.com/fastify/fastify/commit/67f6c9b32cb3623d3c9470cc17ed830dd2f083d7"
        },
        {
          "url": "https://httpwg.org/specs/rfc9110.html#field.content-type"
        },
        {
          "url": "https://github.com/advisories/GHSA-573f-x89g-hqp9"
        },
        {
          "url": "https://cna.openjsf.org/security-advisories.html"
        },
        {
          "url": "https://www.cve.org/CVERecord?id=CVE-2026-3419"
        }
      ],
      "title": "Fastify\u0027s Missing End Anchor in \"subtypeNameReg\" Allows Malformed Content-Types to Pass Validation",
      "x_generator": {
        "engine": "cve-kit 1.0.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "ce714d77-add3-4f53-aff5-83d477b104bb",
    "assignerShortName": "openjs",
    "cveId": "CVE-2026-3419",
    "datePublished": "2026-03-06T17:50:58.714Z",
    "dateReserved": "2026-03-01T18:56:49.613Z",
    "dateUpdated": "2026-03-06T17:54:33.542Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2",
  "vulnerability-lookup:meta": {
    "nvd": "{\"cve\":{\"id\":\"CVE-2026-3419\",\"sourceIdentifier\":\"ce714d77-add3-4f53-aff5-83d477b104bb\",\"published\":\"2026-03-06T18:16:22.213\",\"lastModified\":\"2026-03-06T18:16:22.213\",\"vulnStatus\":\"Received\",\"cveTags\":[],\"descriptions\":[{\"lang\":\"en\",\"value\":\"Fastify 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\\nImpact:\\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\\nWorkarounds:\\nDeploy a WAF rule to protect against this\\n\\nFix:\\n\\nThe fix is available starting with v5.8.1.\"}],\"metrics\":{\"cvssMetricV31\":[{\"source\":\"ce714d77-add3-4f53-aff5-83d477b104bb\",\"type\":\"Secondary\",\"cvssData\":{\"version\":\"3.1\",\"vectorString\":\"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N\",\"baseScore\":5.3,\"baseSeverity\":\"MEDIUM\",\"attackVector\":\"NETWORK\",\"attackComplexity\":\"LOW\",\"privilegesRequired\":\"NONE\",\"userInteraction\":\"NONE\",\"scope\":\"UNCHANGED\",\"confidentialityImpact\":\"NONE\",\"integrityImpact\":\"LOW\",\"availabilityImpact\":\"NONE\"},\"exploitabilityScore\":3.9,\"impactScore\":1.4}]},\"weaknesses\":[{\"source\":\"ce714d77-add3-4f53-aff5-83d477b104bb\",\"type\":\"Secondary\",\"description\":[{\"lang\":\"en\",\"value\":\"CWE-185\"}]}],\"references\":[{\"url\":\"https://cna.openjsf.org/security-advisories.html\",\"source\":\"ce714d77-add3-4f53-aff5-83d477b104bb\"},{\"url\":\"https://github.com/advisories/GHSA-573f-x89g-hqp9\",\"source\":\"ce714d77-add3-4f53-aff5-83d477b104bb\"},{\"url\":\"https://github.com/fastify/fastify/commit/67f6c9b32cb3623d3c9470cc17ed830dd2f083d7\",\"source\":\"ce714d77-add3-4f53-aff5-83d477b104bb\"},{\"url\":\"https://github.com/fastify/fastify/security/advisories/GHSA-573f-x89g-hqp9\",\"source\":\"ce714d77-add3-4f53-aff5-83d477b104bb\"},{\"url\":\"https://httpwg.org/specs/rfc9110.html#field.content-type\",\"source\":\"ce714d77-add3-4f53-aff5-83d477b104bb\"},{\"url\":\"https://www.cve.org/CVERecord?id=CVE-2026-3419\",\"source\":\"ce714d77-add3-4f53-aff5-83d477b104bb\"}]}}"
  }
}


Log in or create an account to share your comment.




Tags
Taxonomy of the tags.




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.