OK, AFAICT there is no bounds checking. When you want to read a message, you give FlatBuffers a bare pointer to the start of the message -- no size. So you can't use this to read data you don't trust I guess.

I think the key use case for FlatBuffers is mostly for very-high-performance communication between a set of processes that you control to scale out high-performance systems into distributed systems while keeping the communication overhead minimal, not for, e.g., communicating between untrusted machines over a public network. So, I don't see that as a huge problem in the key use case.