Cross-Site Request Forgery (CSRF)

Summary

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, in versions prior to 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 the execution of operations within the context of the victim's session, and in extreme scenarios can lead to unauthorized access to users’ accounts. SvelteKit 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 is now performing validation on the `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 resolves sees could be `PUT`/`PATCH`/`DELETE` when the browser issues a `POST` request.