Description
Fastify incorrectly accepts malformed `Content-Type` headers containing trailing characters after the subtype token, in violation of RFC 9110 ยง8.3.1(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.
INFO
Published Date :
2026-03-06T17:50:58.714Z
Last Modified :
2026-03-09T14:55:21.011Z
Source :
openjs
AFFECTED PRODUCTS
The following products are affected by CVE-2026-3419 vulnerability.
| Vendors | Products |
|---|---|
| Fastify |
|
REFERENCES
Here, you will find a curated list of external links that provide in-depth information to CVE-2026-3419.
