I know that certificates and signatures are really important for preventing Man-in-the-middle attacks, among other things.
I am not concerned about a third party reading the transmission, only altering it. Imagine data that is nowhere confidential, just has to be accurate.
If an application is running on a user computer on the intranet and is communicating with another intranet endpoint. And for the sake of the question, you can assume that everyone on the inside is trustable. Is a man-in-the-middle attack a real risk? Could someone on the outside somehow see the request and fake a response?
I am interested in the intranet part of it. Intuitively, I would guess that it is not possible, let alone risky, but I could be wrong.
So first of all, is it possible? Second of all, is it reasonably risky?
An explanation of how it could be done, if it can, would be appreciated.