See here this thread. Maybe it helps a bit, especially the Ddwrt part or openwrt.
Or this:
I highly doubt that Comcast or any ISP for that matter pushes firmware updates to customer owned devices.
It is illegal to do that as you own the hardware.
While certain parts of the firmware (bootfile) IS Comcast owned, it has nothing to do with the rest of it.
It’s a complex (kinda secret process) on how the ISP network communicates with the device once connected to the network (hence the limited brands and models that the ISP supports).
The ISP provided bootfile only has access to a low level section of the device (call it a bios to kinda get the picture) where it authorizes the device, sets the speed tier, measures connection parameters and resets the device.
Long story short ISP has access only to “bios” and NEVER updates your “OS” on your device.
It does it on the devices you would lease from them.
Perhaps, it’s a Netgear thing.
Looks like a pattern to me... this would be the third report this week for the same issue.