what security procedures does the GL-AR150 have in place to protect its firmware?
Not sure what you want. Could you please explain more details?
First of all, the GL firmware is compiled C code and the source is proprietary. Qualcomm and other drivers that are also proprietary are included in the router firmware but no sources are available. Other files are stock OpenWrt and any changes are in the GL github for each firmware.
The V3 firmware checks some hardware id’s to make sure the device in genuine.
Firmware flashing does not have any checks apart from usual checksums, since the user can flash their own firmware. Automatic firmware updates could be intercepted in worst case, but the user can download the firmware from the GL site manually if paranoid and flash it manually.
Hope that helps
Can you explain this more fully, as in my experience this is not the case.