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Fencer Intel
critical 9.1

CVE-2019-15803 json

An issue was discovered on Zyxel GS1900 devices with firmware before 2.50(AAHH.0)C0.

published 6y ago modified 4mo ago also EUVD-2019-6722

cvss
9.1
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
1.3%
EPSS 1.3% chance of exploitation in 30 days, percentile 71%
public exploits
0
none known

Summary

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.

Patch / fix

  • zyxel gs1900-8_firmware 2.50\(aahh.0\)c0
  • zyxel gs1900-8hp_firmware 2.50\(aahi.0\)c0
  • zyxel gs1900-10hp_firmware 2.50\(aazi.0\)c0
  • zyxel gs1900-16_firmware 2.50\(aahj.0\)c0
  • zyxel gs1900-24e_firmware 2.50\(aahk.0\)c0
  • zyxel gs1900-24_firmware 2.50\(aahl.0\)c0
  • zyxel gs1900-24hp_firmware 2.50\(aahm.0\)c0
  • zyxel gs1900-48_firmware 2.50\(aahn.0\)c0
  • zyxel gs1900-48hp_firmware 2.50\(aaho.0\)c0

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Exploit prediction

1.32% chance of exploitation in the next 30 days, higher than 71% of all scored CVEs (FIRST EPSS, 2026-11-09).

Exploits and checks

  • jasper.la https://jasper.la/exploring-zyxel-gs1900-firmware-with-ghidra.html referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
NVD 3.1 9.1 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
NVD 2.0 6.4 AV:N/AC:L/Au:N/C:P/I:P/A:N

Classification

Weakness

References

Sources

Fencer Intel keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.