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'.

Affected: npm: fastify

### Impact

The attacker can use the incorrect `Content-Type` to bypass the `Pre-Flight` checking of `fetch`. `fetch()` requests with Content-Type’s [essence](https://mimesniff.spec.whatwg.org/#mime-type-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](https://fetch.spec.whatwg.org/#simple-header), and therefore they could lead to a Cross-Site Request Forgery attack.

### Patches For `4.x` users, please update to at least `4.10.2` For `3.x` users, please update to at least `3.29.4`

### Workarounds

Implement Cross-Site Request Forgery protection using [`@fastify/csrf`](https://www.npmjs.com/package/@fastify/csrf).

### References

Check out the HackerOne report: https://hackerone.com/reports/1763832.

### For more information

[Fastify security policy](https://github.com/fastify/fastify/security/policy)