I was wondering how a device (eg. RPi or similar board could be built/configured in a way that when you plug it to a LAN (or connect Wifi) it let's you remotely access the LAN (like VPN, but without the ports open on the main router) and then leave behind. I am thinking RPi in an laptop charger that has (how strange?) an ethernet cable connected, or an empty NAS case placed directly to others (huh, since when do we have three NAS? Well whatever...). Endless possibilities here.
Of course you'd have to have physical access to the targeted LAN but only for a couple of minutes. Possible white hat activities are: Testing if your client has a good IP-device surveillance system, if he/she checks for suspicious up/down connections, physical access pentesting without being physically there and so on.
I am imagening some sort of reversed VPN, as you don't need to open ports if your reaching out to a VPN-server... It can definitely be done (and exists probably already) but I am not googling correctly. I'd suppose a Unix distro on such a board is a good start, but are there opensource projects that eventually have done it? Or what protocols/packets could you use to achieve something similar?
Thanks for ideas or links, I appreciate everything, and if I posted in the wrong forum, place or whatever I could have possibly done wrong let me know,