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MQTT stands for MQ Telemetry Transport. It is a publish/subscribe, **extremely simple and lightweight messaging protocol**, designed for constrained devices and low-bandwidth, high-latency or unreliable networks. The design principles are to minimise network bandwidth and device resource requirements whilst also attempting to ensure reliability and some degree of assurance of delivery. These principles also turn out to make the protocol ideal of the emerging “machine-to-machine” (M2M) or “Internet of Things” world of connected devices, and for mobile applications where bandwidth and battery power are at a premium.
MQTT brokers send a **CONNACK** packet in **response** to a CONNECT packet. The **return code 0x00** indicates the credentials are valid and the return code **0x05 indicates they aren't. 0x05 example:**
**Authentication is totally optional** and even if authentication is being performed, **encryption is not used by default** (credentials are sent in clear text). MITM attacks can still be executed to steal passwords.
To connect to a MQTT service you can use: [https://github.com/bapowell/python-mqtt-client-shell](https://github.com/bapowell/python-mqtt-client-shell) and subscribe yourself to all the topics doing:
- Do you work in a **cybersecurity company**? Do you want to see your **company advertised in HackTricks**? or do you want to have access to the **latest version of the PEASS or download HackTricks in PDF**? Check the [**SUBSCRIPTION PLANS**](https://github.com/sponsors/carlospolop)!
- **Join the** [**💬**](https://emojipedia.org/speech-balloon/) [**Discord group**](https://discord.gg/hRep4RUj7f) or the [**telegram group**](https://t.me/peass) or **follow** me on **Twitter** [**🐦**](https://github.com/carlospolop/hacktricks/tree/7af18b62b3bdc423e11444677a6a73d4043511e9/\[https:/emojipedia.org/bird/README.md)[**@carlospolopm**](https://twitter.com/carlospolopm)**.**