EEF-CVE-2026-82758

## Summary

Improper Authentication vulnerability in ash-project ash\_authentication\_oauth2\_server allows an unauthenticated attacker to register OAuth clients even when Dynamic Client Registration is gated by an initial access token.

resolve\_secret/3 in AshAuthentication.Oauth2Server (reached through \_\_resolve\_secret\_\_!) treated any return other than {:ok, \_} or :error from a configured {module, function, args} or 2-arity-function secret provider as a valid secret, wrapping nil, false, or "" as {:ok, value}. When the initial\_access\_token resolves to such an empty value, POST /oauth/register compares the presented bearer token against it and the comparison passes with no token supplied, so registration is open although it was configured closed. The same fail-open affected other resolved secrets such as signing\_secret.

This issue affects ash\_authentication\_oauth2\_server: from 0.1.0 before 0.3.1.

## Configuration

Reachable only when the server configures an initial\_access\_token (so Dynamic Client Registration is meant to require one) and the configured secret provider returns an empty value (nil, false, or "") or an {:error, \_} for it, rather than a non-empty binary.