CVE intelligence and bounded remediation

CVE-2021-35033 — Zyxel Nbg6818 Firmware security vulnerability

High CVSS 7.8

A vulnerability in specific versions of Zyxel NBG6818, NBG7815, WSQ20, WSQ50, WSQ60, and WSR30 firmware with pre-configured password management could allow an attacker to obtain root access of the device, if the local attacker dismantles the device and uses a USB-to-UART cable to connect the device, or if the remote assistance feature had been enabled by an authenticated user.

Severity
High
CVSS
7.8 (3.1)
Published
2021-11-23
CISA KEV
Not currently listed
Ecosystem
operating-system
Weaknesses
CWE-260, CWE-287

Affected products

  • zyxel / nbg6818_firmware
  • zyxel / nbg7815_firmware
  • zyxel / wsq20_firmware
  • zyxel / wsq50_firmware
  • zyxel / wsq60_firmware
  • zyxel / wsr30_firmware

Matched remediation archetype

Authentication bypass and missing authentication

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Check exposure

  • Map every affected endpoint and protocol path, including alternate ports, legacy routes, recovery flows, service accounts, and machine-to-machine access.
  • Confirm which deployments enable the affected authentication mode and whether the interface is reachable from untrusted networks.
  • Review session, token, credential, and proxy trust configuration without attempting account takeover.

Remediate safely

  • Apply the supported fix and centralize fail-closed authentication before protected request handling.
  • Remove default or embedded credentials, rotate affected secrets and sessions, and bind authentication decisions to the intended audience and channel.
  • Add negative tests for alternate routes, malformed or absent credentials, recovery flows, and proxy-derived identity.

Authoritative sources

Complete CVE record and remediation plan

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