CVE-2021-35029: Zyxel USG1000 Firmware

Critical severity, CVSS 9.8. EPSS: 2.3% chance of exploitation in the next 30 days.

An authentication bypasss vulnerability in the web-based management interface of Zyxel USG/Zywall series firmware versions 4.35 through 4.64 and USG Flex, ATP, and VPN series firmware versions 4.35 through 5.01, which could allow a remote attacker to execute arbitrary commands on an affected device.

Affected products

Zyxel USG1000 Firmware: from 4.35, up to and including 4.64
Zyxel USG100 Firmware: from 4.35, up to and including 4.64
Zyxel USG1100 Firmware: from 4.35, up to and including 4.64
Zyxel USG110 Firmware: from 4.35, up to and including 4.64
Zyxel USG1900 Firmware: from 4.35, up to and including 4.64
Zyxel USG20-VPN Firmware: from 4.35, up to and including 5.01
Zyxel USG2000 Firmware: from 4.35, up to and including 4.64
Zyxel USG200 Firmware: from 4.35, up to and including 4.64
Zyxel USG20 Firmware: from 4.35, up to and including 4.64
Zyxel USG20W-VPN Firmware: from 4.35, up to and including 5.01
Zyxel USG20W Firmware: from 4.35, up to and including 4.64
Zyxel USG210 Firmware: from 4.35, up to and including 4.64
Zyxel USG2200-VPN Firmware: from 4.35, up to and including 5.01
Zyxel USG300 Firmware: from 4.35, up to and including 4.64
Zyxel USG310 Firmware: from 4.35, up to and including 4.64
Zyxel USG40 Firmware: from 4.35, up to and including 4.64
Zyxel USG40W Firmware: from 4.35, up to and including 4.64
Zyxel USG50 Firmware: from 4.35, up to and including 4.64
Zyxel USG60 Firmware: from 4.35, up to and including 4.64
Zyxel USG60W Firmware: from 4.35, up to and including 4.64
Zyxel Usg Flex 100 Firmware: from 4.35, up to and including 5.01
Zyxel Usg Flex 100w Firmware: from 4.35, up to and including 5.01
Zyxel Usg Flex 200 Firmware: from 4.35, up to and including 5.01
Zyxel Usg Flex 500 Firmware: from 4.35, up to and including 5.01
Zyxel Usg Flex 700 Firmware: from 4.35, up to and including 5.01
and 12 more

Published 2021-07-02. Last modified 2026-06-17.