I mean a normal passenger on a normal plane making a normal trip to an office building and finding a hidden location where to tape a small box with an arduino in it. Maybe even on the outside so you can use solar power? Though it only needs to last long enough to compromise a machine inside the network.

This would be nothing new, I remember ages ago in the days of WEP that you could buy a small box that would collect enough handshakes to let you crack the WEP password.