A vulnerability in FiberHome GPON ONU HG6145F1 RP4423 allows the device's factory default Wi-Fi password (WPA/WPA2 pre-shared key) to be predicted from the SSID. The device generates default passwords using a deterministic algorithm that derives the router passphrase from the SSID, enabling an attacker who can observe the SSID to predict the default password without authentication or user interaction.