Description
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.
Published: 2026-03-06
Score: 5.3 Medium
EPSS: < 1% Very Low
KEV: No
Impact: Bypass Content-Type Validation
Action: Apply Patch
AI Analysis

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Remediation

No vendor fix or workaround currently provided.

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Tracking

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Advisories
Source ID Title
Github GHSA Github GHSA GHSA-573f-x89g-hqp9 Fastify's Missing End Anchor in "subtypeNameReg" Allows Malformed Content-Types to Pass Validation
History

Wed, 18 Mar 2026 19:15:00 +0000

Type Values Removed Values Added
CPEs cpe:2.3:a:fastify:fastify:*:*:*:*:*:node.js:*:*

Mon, 09 Mar 2026 15:30:00 +0000

Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'yes', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}


Mon, 09 Mar 2026 10:15:00 +0000

Type Values Removed Values Added
First Time appeared Fastify
Fastify fastify
Vendors & Products Fastify
Fastify fastify

Sat, 07 Mar 2026 12:15:00 +0000

Type Values Removed Values Added
Weaknesses CWE-625
References
Metrics threat_severity

None

threat_severity

Moderate


Fri, 06 Mar 2026 18:15:00 +0000

Type Values Removed Values Added
Description 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.
Title Fastify's Missing End Anchor in "subtypeNameReg" Allows Malformed Content-Types to Pass Validation
Weaknesses CWE-185
References
Metrics cvssV3_1

{'score': 5.3, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N'}


cve-icon MITRE

Status: PUBLISHED

Assigner: openjs

Published:

Updated: 2026-03-09T14:55:21.011Z

Reserved: 2026-03-01T18:56:49.613Z

Link: CVE-2026-3419

cve-icon Vulnrichment

Updated: 2026-03-09T14:55:17.583Z

cve-icon NVD

Status : Analyzed

Published: 2026-03-06T18:16:22.213

Modified: 2026-03-18T19:11:46.967

Link: CVE-2026-3419

cve-icon Redhat

Severity : Moderate

Publid Date: 2026-03-06T17:50:58Z

Links: CVE-2026-3419 - Bugzilla

cve-icon OpenCVE Enrichment

Updated: 2026-04-16T11:30:15Z

Weaknesses