GHSA-573f-x89g-hqp9 Fastify's Missing End Anchor in "subtypeNameReg" Allows Malformed Content-Types to Pass Validation

• npm fastify: >= 5.7.2, < 5.8.1 → fixed in 5.8.1

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.