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.

Affected: npm: @sveltejs/kit

### Summary 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 it’s users. The protection is implemented at `kit/src/runtime/server/respond.js#L52`. While the implementation does a sufficient job in mitigating common CSRF attacks, the protection can be bypassed by simply specifying a different `Content-Type` header value.

### Details The CSRF protection is implemented using the code shown below.

```js const forbidden = // (1) request.method === 'POST' && // (2) request.headers.get('origin') !== url.origin && // (3) is_form_content_type(request);

if (forbidden) { // (4) const csrf_error = error(403, `Cross-site ${request.method} form submissions are forbidden`); if (request.headers.get('accept') === 'application/json') { return json(csrf_error.body, { status: csrf_error.status }); } return text(csrf_error.body.message, { status: csrf_error.status }); } ``` If the incoming request specifies a POST method (1), the protection will compare the server’s origin with the value of the HTTP `Origin` header (2). A mismatch between these values signals that a potential attack has been detected. The final check is performed on the request’s `Content-Type` header (3) whether the value is either `application/x-www-form-urlencoded` or `multipart/form-…