Lightning coordinate finder

The bug

Because lightning uses BlockPos on impact, you can easily "exploit" that by sending a message to the client with the position of the lightning impact (see example). There's no limit on this either, as it's global. If you were at 7 million blocks away from a player, and a lightning bolt would strike at the players location, you would know the exact location.

Example

Based on 1.12.2 MCP, but can confirm this works in latest 1.14 snapshot.

See attachment, you basically get the coordinates from the impact using the blockpos.
Fully chat message looks like:

Minecraft.getMinecraft().player.sendChatMessage("X: " +blockpos.getX() + " Y: " + blockpos.getY() + " Z: " + blockpos.getZ());