SvelteKit is a web development framework. 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. While the implementation does a sufficient job in mitigating common CSRF attacks, prior to version 1.15.1, the protection can be bypassed by simply specifying a different Content-Type header value.
If abused, this issue will allow malicious requests to be submitted from third-party domains, which can allow execution of operations within the context of the victim's session, and in extreme scenarios can lead to unauthorized access to users’ accounts.
SvelteKit 1.15.1 updates the is_form_content_type function call in the CSRF protection logic to include text/plain. As additional hardening of the CSRF protection mechanism against potential method overrides, SvelteKit 1.15.1 is now performing validation on PUT, PATCH and DELETE methods as well. This latter hardening is only needed to protect users who have put in some sort of ?_method= override feature themselves in their handle hook, so that the request that resolve sees could be PUT/PATCH/DELETE when the browser issues a POST request.