Astro is a web framework for content-driven websites. In affected versions a bug in Astro’s CSRF-protection middleware allows requests to bypass CSRF checks. When the `security.checkOrigin` configuration option is set to `true`, Astro middleware will perform a CSRF check. However, a vulnerability exists that can bypass this security. 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. Additionally, the `Content-Type` header is not required for a request. This issue has been addressed in version 4.16.17 and all users are advised to upgrade. There are no known workarounds for this vulnerability.

Affected: npm: 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](https://developer.mozilla.org/en-US/docs/Web/HTTP/CORS#simple_requests) and will not perform preflight validation. In this case, CSRF is not…