SvelteKit vulnerable to Cross-Site Request Forgery
Date: 2023-04
Affected: npm/@sveltejs/kit
Attack vector: other
Category: vulnerability-disclosure
Severity: High
CVE: CVE-2023-29003
CWE: CWE-184
CWE-352
CVSS: 8.8 (CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H)

### 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-d


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