{"id":"CVE-2026-3419","details":"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.\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.","aliases":["GHSA-573f-x89g-hqp9"],"modified":"2026-04-02T13:29:22.512632Z","published":"2026-03-06T18:16:22.213Z","related":["GHSA-573f-x89g-hqp9"],"references":[{"type":"ADVISORY","url":"https://cna.openjsf.org/security-advisories.html"},{"type":"ADVISORY","url":"https://github.com/fastify/fastify/security/advisories/GHSA-573f-x89g-hqp9"},{"type":"ADVISORY","url":"https://www.cve.org/CVERecord?id=CVE-2026-3419"},{"type":"FIX","url":"https://github.com/advisories/GHSA-573f-x89g-hqp9"},{"type":"FIX","url":"https://github.com/fastify/fastify/commit/67f6c9b32cb3623d3c9470cc17ed830dd2f083d7"},{"type":"ARTICLE","url":"https://httpwg.org/specs/rfc9110.html#field.content-type"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://github.com/fastify/fastify","events":[{"introduced":"e1e4fe75910c36e1b9ebb87026ca16c053a9c1f2"},{"fixed":"073ff8132f350aaa53935231019499e983cb9794"},{"fixed":"67f6c9b32cb3623d3c9470cc17ed830dd2f083d7"}],"database_specific":{"versions":[{"introduced":"5.7.2"},{"fixed":"5.8.1"}]}}],"versions":["v5.7.2","v5.7.3","v5.7.4","v5.8.0"],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-3419.json"}}],"schema_version":"1.7.5","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N"}]}