Yes, you have to go to the top of the pillar in Undernet 4, past Beastman's security cube. To get past it, fight Beastman at the deadend in Scilab 1. Then, go to Lan's doghouse and use the Sneakrun subchip. You'll find Beastman and beat him. Then, you can open the cube.
props to pokemonruler for the sweet sig and avatar