An issue was discovered on V-SOL V1600D V2.03.69 and V2.03.57, V1600D4L V1.01.49, V1600D-MINI V1.01.48, V1600G1 V2.0.7 and V1.9.7, and V1600G2 V1.1.4 OLT devices. TELNET is offered by default but SSH is not always available. An attacker can intercept passwords sent in cleartext and conduct a man-in-the-middle attack on the management of the appliance.