The Message Queuing Telemetry Transport (MQTT) protocol is a machine-to-machine communication protocol widely used in Internet of Things (IoT) applications due to its lightweight nature. However, ensuring security in such systems remains a challenge due to the resource-constrained environments it operates in. This paper presents the design and implementation of a packet filtering firewall for MQTT traffic by detecting and filtering packets early in the packet processing pipeline using a Linux feature called the extended Berkeley Packet Filter (eBPF) with established performance implications.