Most original firmware from 2017-2018 has known vulnerabilities (Dirty COW, KRACK, BlueBorne). 2021 builds integrate Google security patches through at least December 2020.
In 2021, firmware updates for S905L2 devices primarily addressed hardware porting and system longevity: amlogic s905l2 firmware 2021
– Unplug the power. Do NOT connect the USB yet. amlogic s905l2 firmware 2021
Enhanced Performance and Security: Amlogic S905L2 Firmware 2021 amlogic s905l2 firmware 2021