Elytra exploit

So basically what I discovered is that the elytra will always sync its client movement to the server, even when there's abnormal movement, and the server won't do anything about it. I've tested it on a couple of my own servers, and a creative server. I have reported the issue to said creative server in hopes it gets patched on their end, and that patch gets spread to other servers, but I have also decided to report it here. With just a little bit of code injected into the head of the update/tick method of the player class, it's possible to give the player infinite flight without the need for rockets or weird angle shenanigans.

The code is as follows:

if(isFallFlying())
{
   if(forwardSpeed > 0)
   {
      Vec3d rotation = getRotationVector();
      Vec3d velocity = getVelocity();

      setVelocity(velocity.add(rotation.x * (0.05F) + (rotation.x * 1.5D - velocity.x) * 0.05F,
      rotation.y * (0.05F) + (rotation.y * 1.5D - velocity.y) * 0.05F,
      rotation.z * (0.05F) + (rotation.z * 1.5D - velocity.z) * 0.05F));
   }
}

And here's a video of it in action (unlisted so it doesn't get out):

https://youtu.be/D0dguTTELQ0