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Vulnerability record · CVE-2019-15803 · published 14 November 2019

CVE-2019-15803: Zyxel gs1900-8 firmware improper authentication vulnerability

Zyxel · Gs1900 8 Firmware

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.

9.1 CVSS 3.1 Critical EPSS 1.3% · top 30.2% CWE-287 · Improper authentication
9.1CVSS 3.1 base score, v2 6.4
1.3%EPSS exploitation probability, 30 days
NoNot in CISA KEV
9Affected product versions listed by NVD
4References, 2 tagged exploit
17 Jun 2026Last modified by NVD

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.

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

Affected products

9 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

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

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Related vulnerabilities

Same products first, then exploited flaws of the same weakness class.

8.8CVE-2026-7273Zyxel gs1900-8 firmware stack-based buffer overflow vulnerabilityA stack-based buffer overflow vulnerability in the CGI program of Zyxel GS1900-48HPv2 firmware versions through 2.90(ABTQ.1)C0 could allow a LAN-base…KEVEPSS 2.5%9.8CVE-2019-15800Zyxel gs1900-8 firmware os command injection vulnerabilityAn issue was discovered on Zyxel GS1900 devices with firmware before 2.50(AAHH.0)C0. Due to lack of input validation in the cmd_sys_traceroute_exec()…EPSS 3.9%9.8CVE-2016-1329Samsung x14j firmware improper authentication vulnerabilityCisco NX-OS 6.0(2)U6(1) through 6.0(2)U6(5) on Nexus 3000 devices and 6.0(2)A6(1) through 6.0(2)A6(5) and 6.0(2)A7(1) on Nexus 3500 devices has hardc…EPSS 3.7%9.8CVE-2015-5989Zyxel gs1900-10hp firmware permissions and access controls vulnerabilityBelkin F9K1102 2 devices with firmware 2.10.17 rely on client-side JavaScript code for authorization, which allows remote attackers to obtain adminis…EPSS 2.8%9.8CVE-2015-5988Zyxel gs1900-10hp firmware vulnerabilityThe web management interface on Belkin F9K1102 2 devices with firmware 2.10.17 has a blank password, which allows remote attackers to obtain administ…EPSS 2.7%8.8CVE-2019-15799Zyxel gs1900-8 firmware improper privilege management vulnerabilityAn issue was discovered on Zyxel GS1900 devices with firmware before 2.50(AAHH.0)C0. User accounts created through the web interface of the device, w…EPSS 2.3%8.8CVE-2016-1302Samsung x14j firmware improper access control vulnerabilityCisco Application Policy Infrastructure Controller (APIC) devices with software before 1.0(3h) and 1.1 before 1.1(1j) and Nexus 9000 ACI Mode switche…EPSS 2.2%8.8CVE-2015-5990Zyxel gs1900-10hp firmware cross-site request forgery vulnerabilityCross-site request forgery (CSRF) vulnerability on Belkin F9K1102 2 devices with firmware 2.10.17 allows remote attackers to hijack the authenticatio…EPSS 0.62%

Source: NIST National Vulnerability Database (record CVE-2019-15803), CISA KEV, FIRST EPSS (scores of 2026-09-26). This page is refreshed as NVD updates the record.