CVE-2019-15803: Improper Authentication

An issue was discovered on Zyxel GS1900 devices with firmware before 2.50AAHH.0C0. Through an undocumented sequence of keypresses, undocumented functionality is triggered. A diagnostics shell is triggered via CTRL-ALT-t, which prompts for the password returned by fdssyspassDebugPasswdret. The...