Modified clients can easily avoid fall damage

What should happen : Falling from a certain height deals fall damage.

What actually happens : Falling generates the appropriate sound but does not deal any damage to the player.

How to reproduce : A modified client tricks the server into believing that he is always on ground by sending the appropriate packet. This does not have to be done on every tick, as illustrated in the following example.

Example (With MCP Mappings) : The following (very simple) piece of code allows the player to completely avoid any fall damage when placed for instance in the onUpdate function of EntityPlayerSP

if (this.fallDistance > 0.0D) this.connection.sendPacket(new CPacketPlayer(true));

Code analysis: See MC-132606