Most seedbox hosting providers and open-source seedbox management panels synchronize the customer's SSH/system password with the Deluge torrent client's daemon auth file (~/.config/deluge/auth). This auth file stores passwords in plaintext in all currently deployed Deluge versions.
The customer's SSH password is therefore stored in cleartext at a known, predictable path inside the user's home directory. Any vulnerability that allows reading files from the user's home directory — past, present, or future — immediately yields the SSH password.
This is not a new Deluge vulnerability. Deluge's plaintext auth file is a known, long-standing design choice (ticket #2442, opened 2014). The problem is the industry practice of placing the SSH password — the keys to the kingdom — into that file.