The IoT news site M2Mnow has an article by Benny Czarny of OPSWAT, discussing the top 3 IoT threat trends, and one of these 3 trends is firmware:
Trend # 3. Increasing firmware hacks
Another trend that we are seeing is firmware hacking: the process of installing rogue firmware on embedded devices. Cisco recently warned customers that hackers are replacing the boot firmware on devices running Cisco’s IOS operating system with a malicious version. The attackers install the malicious version to prevent reboots from wiping IOS infections. Now that Point of Sale systems (POS) have gone mobile, these too have become a target for hackers. Although the possibility of firmware hacking has been known for some time, actual real-world attacks have been rare until now.