CVE-2026-58399

@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 TRUSTEDMTLSSERVICES allowlist).

Updated consumers (rest, graphql, dns-client) for mTLS support.

Unit tests added for sanitization + mTLS path.