  Internet-of-Things devices, ranging from smart home assistants to health
devices, are pervasive: Forecasts estimate their number to reach 29 billion by
2030. Understanding the security of their machine-to-machine communication is
crucial. Prior work focused on identifying devices' vulnerabilities or proposed
protocol-specific solutions. Instead, in this paper, we investigate the
security of backends speaking Internet-of-Things (IoT) protocols at scale, that
is, the backbone of the entire IoT ecosystem.
  We focus on three real-world protocols used by IoT for our large-scale
analysis: MQTT, CoAP, and XMPP. We gather a dataset of over 337,000 backends,
augment it with geographical and provider data, and perform non-invasive active
measurements to investigate three major security threats: information leakage,
weak authentication, and denial of service. Our results provide quantitative
evidence of a problematic immaturity in the IoT security ecosystem. Among other
issues, we find that 9.44% backends expose information, 30.38% CoAP-speaking
backends are vulnerable to denial of service attacks, and 99.84% of
MQTT-speaking and XMPP-speaking backends use insecure transport protocols (only
0.16% adopt TLS, of which 70.93% adopt a vulnerable version).
