MQTT exposure check: is a broker reachable without authentication?
Will probe whether a given host accepts anonymous MQTT connections on the standard plain (1883) or TLS (8883) ports, without subscribing to any topic or reading its content, and explain what an open broker exposes if found. Coming with the AdminKit Check API.
Whether a host accepts an anonymous MQTT connection on 1883/8883 — never subscribing to or reading topic content.
- Anonymous CONNECT handshake only, nothing read or written
- Plain-language explanation of what an open broker exposes
- Ships with the AdminKit Check API, built on the same checks/mqtt library as the broker product
Next step
Also see Modbus exposure, or check other commonly exposed ports.
How it works and limits
MQTT is the publish/subscribe protocol most IoT devices and home-automation hubs use to talk to each other and to the cloud. Many broker deployments ship with anonymous access enabled by default for ease of setup, and are never locked down before going live on the internet.
What it will check
- Whether a host accepts an anonymous MQTT
CONNECTon the standard ports (1883 plain, 8883 TLS). - Nothing beyond that handshake: it will not subscribe to any topic or read any message content.
- A plain-language explanation of what an anonymous-access broker exposes if found open.
Why this is not live yet
It ships with the AdminKit Check API, built on the same checks/mqtt library used by AdminKit’s broker product, so
the probe logic is shared and tested once rather than duplicated.
Check manually today
With the mosquitto client tools installed:
mosquitto_sub -h <host> -p 1883 -t '#' -v -C 1If this connects and prints a message (or simply connects without an authentication error) within a few seconds, the broker accepts anonymous connections — only run this against a broker you own or are authorized to test.
Frequently asked questions
Why is this tool not live yet?
It ships with the AdminKit Check API (plan milestone M5), using the checks/mqtt library built in parallel (plan milestone M3).
Why does an open MQTT broker matter?
Anyone who can reach it can read and publish to every topic, which on IoT devices often means reading sensor data or sending commands.