Many components are networked, but the networking protocols used for critical systems are very different from anything else. Eg there is no "dynamic" addressing or routing, unlike ethernet there is no ARP, no DHCP, because every single component is known. Messages are strictly filtered and prioritized to ensure enough bandwidth for critical applications. Even if you were "on the same wire"...you'd have a very hard time. If you wanted to interfere, I'd say you would need physical access to some components, and re-flash the firmware. You can't do that from a passenger seat. Also the real-time operating systems used are not something many are familiar with. It would take a huge effort.
Some data flows from aircraft system to IFE, but it's one way.