An issue was discovered on Zyxel GS1900 devices with firmware before 2.50(AAHH.0)C0. 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 fds_sys_passDebugPasswd_ret(). The firmware contains access control checks that determine if remote users are allowed to access this functionality. The function that performs this check (fds_sys_remoteDebugEnable_ret in libfds.so) always return TRUE with no actual checks performed. The diagnostics menu allows for reading/writing arbitrary registers and various other configuration parameters which are believed to be related to the network interface chips.
When an actor claims to have a given identity, the product does not prove or insufficiently proves that the claim is correct.
| Name | Vendor | Start Version | End Version |
|---|---|---|---|
| Gs1900-8_firmware | Zyxel | * | 2.50(aahh.0)c0 (excluding) |