Client - Server System is lacking client data control

The minecraft server is not validating that the client's movement are correct, thus causing massive exploits in many modified clients.

Additionally the server is not validating creative mode items, whether one is looking at the position a block is placed, whether one is looking at its enemy when hitting (use client ping to know where the enemy is for the client), whether blocks are inbetween the attacker and the attacked, whether the client is trying to regenerate health too quickly, whether the client moved through blocks (not checked correctly), breaking multiple blocks
simultaneously, etc, etc. Just grab a cheat client like Wurst and see what is possible and fix those things please with proper vaildation.