AdTran 834-5 HDC17600021F1 (SmartOS 11.1.1.1) devices enable the SSH service by default and have a hidden, undocumented, hard-coded support account whose password is based on the devices MAC address. All of the devices internet interfaces share a similar MAC address that only varies in their final octet. This allows network-adjacent attackers to derive the support user's SSH password by decrementing the final octet of the connected gateway address or via the BSSID. An attacker can then execute arbitrary OS commands with root-level privileges. NOTE: The vendor states that there is no intended functionality allowing an attacker to execute arbitrary OS Commands with root-level privileges. The vendor also states that this issue was fixed in SmartOS 12.5.5.1.