The Apocalypse Exploit is an exploit that was discovered by the players fr1kin, babbaj, and 0x22 in late March 2017. The exploit creates a situation in which a player is in multiple places at once (player superposition). Because of this, a player using the exploit was able to load twice as many chunks as they would normally, in addition to making the server constantly divide the player's position by 8 until it crashed due to the number getting too long (eg. if the outcome was 3, the server would keep adding additional 3s until it would crash). This is also known as a floating-point overflow, similar to integer overflow, but caused by the number of digits after the decimal.
The exploit involved performing the
/kill command while either the player was riding an animal or vehicle in the nether. This would result in the player being respawned in two places at once server-side. These locations would be near the portal where the player entered the nether and the spawn point of the player. This would confuse the server and cause it to start dividing the nether coordinates of the player by 8 until finally crashing due to the number being too long or invalid.