Skip to content

Insufficient Cross-Site Request Forgery Protection

Critical
benmccann published GHSA-5p75-vc5g-8rv2 Apr 4, 2023

Package

npm @sveltejs/kit (npm)

Affected versions

<= 1.15.0

Patched versions

1.15.1

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.

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.

Severity

Critical

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
Required
Scope
Changed
Confidentiality
High
Integrity
High
Availability
None

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:N

CVE ID

CVE-2023-29003

Weaknesses

No CWEs

Credits