CVE-2023-29008: SvelteKit framework has Insufficient CSRF protection for CORS requests

The SvelteKit framework offers developers an option to create simple REST APIs. This is done by defining a +server.js file, containing endpoint handlers for different HTTP methods.

SvelteKit provides out-of-the-box cross-site request forgery (CSRF) protection to its users. The protection is implemented at kit/src/runtime/server/respond.js. While the implementation does a sufficient job of mitigating common CSRF attacks, the protection can be bypassed by simply specifying an upper-cased Content-Type header value. The browser will not send uppercase characters on form submission, but this check does not block all expected cross-site requests: https://developer.mozilla.org/en-US/docs/Web/HTTP/CORS#simple_requests