Fastify is a web framework with minimal overhead and plugin architecture. The attacker can use the incorrect `Content-Type` to bypass the `Pre-Flight` checking of `fetch`. `fetch()` requests with Content-Type’s essence as "application/x-www-form-urlencoded", "multipart/form-data", or "text/plain", could potentially be used to invoke routes that only accepts `application/json` content type, thus bypassing any CORS protection, and therefore they could lead to a Cross-Site Request Forgery attack. This issue has been patched in version 4.10.2 and 3.29.4. As a workaround, implement Cross-Site Request Forgery protection using `@fastify/csrf'.

https://github.com/fastify/fastify/commit/62dde76f1f7aca76e38625fe8d983761f26e6fc9
https://www.npmjs.com/package/@fastify/csrf
https://github.com/fastify/fastify/security/advisories/GHSA-3fjj-p79j-c9hh