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.
References
TarPeg007 Reporter
jsumners Remediation developer
mcollina Coordinator
UlisesGascon Remediation reviewer
Description
Fastify incorrectly accepts malformed
Content-Typeheaders containing trailing characters after the subtype token, in violation of RFC 9110 §8.3.1. For example, a request sent withContent-Type: application/json garbagepasses validation and is processed normally, rather than being rejected with415 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-Typeheaders 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.
References