practically all modern implementations of LANs are insecure
Meaning that most networks by default are subject and not limited to the following network attack vectors:
- ARP Cache Poisoning - Resulting in a full-duplex MiTM attack
- DHCP Spoofing - Resuting in a full-duplex MiTM attack
- Port Stealing - Resulting in a OSI Layer 2 (switches only) full-duplex MiTM attack
- MAC Flooding - Resulting in the reversion of a switch device to act as a hub instead, to the the overloading of the CAM tables
- ARP Isolation - resulting in a instant single packet DoS of any node on the network (sever included)
- DHCP Exhaustion - resulting in a very rapid DoS on the entire network caused by all IP leases to be falsely occupied
- etc etc etc
In short, the default for practically all LANs is insecure, this is because secure is a pain in the ass for even intermediate to semi-advanced net-admins (i still think these people suck at their job but whatever).
Anyways, launch a MiTM, shift through the data of tcpdump or wireshark, find some credentials and log in as a teacher collect $100 and smile.
Also, seeing how it is indeed a LAN and working on the assumption that Websense bases it's network authentication off of the only thing it can (ethernet data) and that it doesn't tunnel data through a custom OSI Layer 7 protocol, you could falsely authenticate yourself as another user on the network. This is as simple (or as hard depending on your access) to find a machine that a teacher is currently authenticated on, take note of that machines MAC address and ip, and spoof you MAC and address to match it. The end result is Websense shouldn't be able to tell the difference between your computer and the teachers computer, the routers and switches should be equally confused but the typical default is to forward in both directions. This is the same method that can be used to bypass pay for access captive portals in hotels and coffee shops.
"If art interprets our dreams, the computer executes them in the guise of programs!" - SICP
“If at first, the idea is not absurd, then there is no hope for it” - Albert Einstein