Vert.x STOMP is a vert.x implementation of the STOMP specification that provides a STOMP server and client. From versions 3.1.0 until 3.9.16 and 4.0.0 until 4.4.2, a Vert.x STOMP server processes client STOMP frames without checking that the client send an initial CONNECT frame replied with a successful CONNECTED frame. The client can subscribe to a destination or publish message without prior authentication. Any Vert.x STOMP server configured with an authentication handler is impacted. The issue is patched in Vert.x 3.9.16 and 4.4.2. There are no trivial workarounds.