EUVD-2026-332292

fkie_cve-2026-58399

@acastellon/auth is an authentication control system for microservices. Versions prior to 2.3.0 appear 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. A fix has been implemented in v2.3.0.

GHSA-gfj5-979r-92pw — @acastellon/auth: Authentication bypass via spoofable headers in validateToken()

Affected: npm: @acastellon/auth

@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). Upda…

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EUVD-2026-332292

fkie_cve-2026-58399

GHSA-gfj5-979r-92pw — @acastellon/auth: Authentication bypass via spoofable headers in validateToken()