---
id: GHSA-gfj5-979r-92pw
title: >-
  @acastellon/auth: Authentication bypass via spoofable headers in
  validateToken()
summary: >-
  @acastellon/auth: Authentication bypass via spoofable headers in
  validateToken()
severity: critical
cwe:
  - CWE-290
vendor: acastellon
product: '@acastellon/auth'
affected:
  - '@acastellon/auth < 2.3.0'
patched:
  - '@acastellon/auth 2.3.0'
published: '2026-06-18'
updated: '2026-06-18'
source: GHSA
sourceUrl: 'https://github.com/advisories/GHSA-gfj5-979r-92pw'
references:
  - url: >-
      https://github.com/antonio-castellon/module-auth/security/advisories/GHSA-gfj5-979r-92pw
  - url: 'https://github.com/antonio-castellon/module-auth/issues/6'
  - url: 'https://www.npmjs.com/package/@acastellon/auth/v/2.3.0'
  - url: 'https://github.com/advisories/GHSA-gfj5-979r-92pw'
tags:
  - ghsa
  - npm
ingestedAt: '2026-06-19T03:39:00.790Z'
ecosystem: npm
---

## Overview

@acastellon/auth v2.2.0 appears to allow an unauthenticated authentication bypass in validateToken() through spoofable auth-user and Host request headers.

The validateToken middleware contains a service-to-service bypass for auth-user: service-brother when req.get('host').startsWith(getHostName()). Both values involved in the check can be influenced by an unauthenticated HTTP client: auth-user is a request header, and Host is also client-controlled. As a result, a remote unauthenticated attacker can send a request with crafted headers and bypass token validation before the normal legacy/JWT/OIDC validation logic runs.

Impact:
An attacker may be able to access routes protected by validateToken() without a valid token. In deployments where downstream services trust auth-user or is-* headers, this may also lead to privilege escalation.

Affected package:
@acastellon/auth v2.2.0

Affected code:
auth.js, validateToken()
The issue is related to the service-brother bypass and getHostName() check.

Example request:
```
GET /protected HTTP/1.1
Host: <configured CNAME or hostname>
auth-user: service-brother
is-admin: true
```

Expected behavior:
The request should require a valid authentication token.

Actual behavior:
The middleware calls next() before token validation.

Fix implemented in v2.3.0+:

Removed the spoofable bypass.
Always sanitize incoming auth-user and is-* headers.
Added mTLS client certificate based service auth (with optional TRUSTED_MTLS_SERVICES allowlist).
Updated consumers (rest, graphql, dns-client) for mTLS support.
Unit tests added for sanitization + mTLS path.

## Affected packages

- `@acastellon/auth < 2.3.0`

## Remediation

Upgrade to a patched release:

- `@acastellon/auth 2.3.0`