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GHSA-5p75-vc5g-8rv2

HighCVSS 8.8 / 10
Published Apr 4, 2023·Last modified Nov 8, 2023
Affected Components(0)

No affected components available

Description

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.

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-data (kit/src/utils/http.js#L71). If all the previous checks pass, the request will be rejected with an 403 error response (4).

The is_form_content_type validation is not sufficient to mitigate all possible variations of this type of attack. If a CSRF attack is performed with the Content-Type header set to text/plain, the protection will be circumvented and the request will be processed by the endpoint handler.

<!-- ### PoC To reproduce this issue, create and run a simple server (by default running on `localhost:3000`) with a POST endpoint handler such as: ```js export async function POST({ request }) { const data = await request.json(); console.log(JSON.stringify(data)); return new Response(String('success')); } ``` Next, save the malicious HTML page: ```html <!DOCTYPE html> <html> <head></head> <body> <h1 id="name"></h1> <form action="http://localhost:3000/api/test" method="POST" enctype="text/plain"> <input type="hidden" name="&#123;&quot;name&quot;&#58;&quot;test" value="&quot;&#44;&quot;age&quot;&#58;123&#125;" /> <input type="submit" value="Submit" /> </form> </body> </html> ``` in a file named `index.html`. Run another web server, using Python’s built in http.server module (`python -m http.server`, by default running on `localhost:8000`), navigate to [http://localhost:8000/index.html](http://localhost:8000/index.html) and click the `Submit` button. Verify that the browser’s URL has changed to `localhost:3000` and that the text `success` is displayed on the screen. Additionally, inspect the console of the SvelteKit web server and verify that the request body (`{"name":"test=","age":123}`) was parsed as valid JSON and printed out. It's worth noting that this attack is possible only for JSON request bodies. Form data sent using `text/plain` will be rejected by the server. -->

Impact

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.

Remediation

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.

Risk Scores
Base Score
8.8

The vulnerability can be exploited over the network without needing physical access. It is easy for an attacker to exploit this vulnerability. An attacker does not need any special privileges or access rights. The attacker needs the user to perform some action, like clicking a link. The impact is confined to the system where the vulnerability exists. There is a high impact on the confidentiality of the information. There is a high impact on the integrity of the data. There is a high impact on the availability of the system.

Threat Intelligence
8.1

Exploitation activity has been observed. Apply available patches or mitigations urgently.

EPSS
0.56%

The exploit probability is very low. The vulnerability is unlikely to be exploited in the next 30 days.

Exploit
Not available

We did not find any exploit available. Neither in GitHub repositories nor in the Exploit-Database.

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High severity
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