{"id":"CVE-2026-3419","aliases":["GHSA-573f-x89g-hqp9"],"url":"https://o3.security/vulnerability/CVE-2026-3419","summary":"Fastify's Missing End Anchor in \"subtypeNameReg\" Allows Malformed Content-Types to Pass Validation","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.","published":"2026-03-06T17:50:58.714Z","modified":"2026-08-12T03:51:23.308226025Z","cvss":{"score":5.3,"severity":"MEDIUM","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N"},"epss":{"score":0.00351,"percentile":0.28672,"asOf":"2026-09-17"},"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"npm","name":"fastify","fixedVersion":"5.8.1"}],"fix":{"url":"https://github.com/fastify/fastify/commit/67f6c9b32cb3623d3c9470cc17ed830dd2f083d7","label":"fastify/fastify@67f6c9b"},"references":[{"type":"WEB","url":"https://httpwg.org/specs/rfc9110.html#field.content-type"},{"type":"WEB","url":"https://www.cve.org/CVERecord?id=CVE-2026-3419"},{"type":"ADVISORY","url":"https://cna.openjsf.org/security-advisories.html"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/3xxx/CVE-2026-3419.json"},{"type":"ADVISORY","url":"https://github.com/advisories/GHSA-573f-x89g-hqp9"},{"type":"ADVISORY","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":"FIX","url":"https://github.com/fastify/fastify/commit/67f6c9b32cb3623d3c9470cc17ed830dd2f083d7"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-08-12T03:51:23.308226025Z"}}