A flaw was found in the AAP Gateway Envoy proxy configuration. The gateway defines two routes to EDA external event streams: /mtls/eda-event-streams/ (which requires a validated TLS client certificate and adds the Subject header from the certificate DN) and /eda-event-streams/ (which has no authentication and ext_authz disabled). The source code at route.py:255 specifies requestHeadersToRemove: ["Subject"] for the non-mTLS route, but this directive is absent from the live xDS configuration delivered to Envoy. As a result, client-supplied Subject headers are forwarded verbatim to the EDA backend. An unauthenticated remote attacker can send a POST request to the non-mTLS route with a spoofed Subject header matching a legitimate client certificate Distinguished Name (DN) to bypass mTLS authentication and inject arbitrary events into protected event streams. The expected DN is leaked in the 403 error response body when an incorrect value is supplied, making exploitation trivial once the event stream UUID is known. Injected events trigger downstream rulebook actions which may include automation execution on managed infrastructure.