...except my cable modem does not share storage with my PC. On the other hand, the baseband and Android system (not to mention the device-specific efs/imei stuff and the user data stuff) are all located on the same emmc on many devices. (Hence the ability to "flash a new radio")
Could the baseband access or change data on the Android partitions or the efs data? I'm not sure, but the articles suggest to me that they could.
Also, my cable modem doesn't share memory with my PC either:
The baseband processor (and thus REX OS) has direct access to the phoneâ(TM)s hardware (speakers, microphones), and also seemingly the ability to write to the same memory as the SoC (or application processor).
Also, unlike your cable modem analogy, which communicates to your router via a known network protocol, the baseband communicates with Android in most cases via the involvement of closed-source, mysterious "binary blobs".
So I guess if your cable modem were fused to your computer, sharing a hard drive, with direct access to its memory and peripherals, and communicating to your computer via a mysterious unauditable binary, then maybe your analogy would hold up.