My assumption is that they're talking about a component that is not the baseband. The baseband itself definitely isn't connected via DMA. I'm trying to make sure we're using the same terminology before I respond.

For what it's worth, at least for Apple phones, I think he's wrong about there being any component that matches the description he's provided that is a memory corruption bug away from being able to overwrite AP memory (and I'm even more sure there's no component that can do that to the SE).

But I'm not sure what exactly they're talking about, so it would be weird to rebut at this point.