CVE-2023-33010: Zyxel Multiple Firewalls Buffer Overflow Vulnerability

Critical severity, CVSS 9.8. Actively exploited: in CISA KEV since 2023-06-05. EPSS: 29% chance of exploitation in the next 30 days.

A buffer overflow vulnerability in the ID processing function in Zyxel ATP series firmware versions 4.32 through 5.36 Patch 1, USG FLEX series firmware versions 4.50 through 5.36 Patch 1, USG FLEX 50(W) firmware versions 4.25 through 5.36 Patch 1, USG20(W)-VPN firmware versions 4.25 through 5.36 Patch 1, VPN series firmware versions 4.30 through 5.36 Patch 1, ZyWALL/USG series firmware versions 4.25 through 4.73 Patch 1, could allow an unauthenticated attacker to cause denial-of-service (DoS) conditions and even a remote code execution on an affected device.

Affected products

Zyxel ATP100 Firmware: from 4.32, before 5.36 (fixed in 5.36); version 5.36 only
Zyxel ATP100W Firmware: from 4.32, before 5.36 (fixed in 5.36); version 5.36 only
Zyxel ATP200 Firmware: from 4.32, before 5.36 (fixed in 5.36); version 5.36 only
Zyxel ATP500 Firmware: from 4.32, before 5.36 (fixed in 5.36); version 5.36 only
Zyxel ATP700 Firmware: from 4.32, before 5.36 (fixed in 5.36); version 5.36 only
Zyxel ATP800 Firmware: from 4.32, before 5.36 (fixed in 5.36); version 5.36 only
Zyxel USG20-VPN Firmware: from 4.30, before 5.36 (fixed in 5.36); version 5.36 only
Zyxel Usg 20w-VPN Firmware: version 5.36 only
Zyxel Usg 40 Firmware: from 4.25, before 4.73 (fixed in 4.73); version 4.73 only
Zyxel Usg 40w Firmware: from 4.25, before 4.73 (fixed in 4.73); version 4.73 only
Zyxel Usg 60 Firmware: from 4.25, before 4.73 (fixed in 4.73); version 4.73 only
Zyxel Usg 60w Firmware: from 4.25, before 4.73 (fixed in 4.73); version 4.73 only
Zyxel Usg Flex 100 Firmware: from 4.50, before 5.36 (fixed in 5.36); version 5.36 only
Zyxel Usg Flex 100w Firmware: version 5.36 only
Zyxel Usg Flex 200 Firmware: from 4.50, before 5.36 (fixed in 5.36); version 5.36 only
Zyxel Usg Flex 500 Firmware: from 4.50, before 5.36 (fixed in 5.36); version 5.36 only
Zyxel Usg Flex 50 Firmware: version 5.36 only
Zyxel Usg Flex 50w Firmware: from 4.25, before 5.36 (fixed in 5.36); version 5.36 only
Zyxel Usg Flex 700 Firmware: from 4.50, before 5.36 (fixed in 5.36); version 5.36 only
Zyxel VPN1000 Firmware: from 4.30, before 5.36 (fixed in 5.36); version 5.36 only
Zyxel VPN100 Firmware: from 4.30, before 5.36 (fixed in 5.36); version 5.36 only
Zyxel VPN300 Firmware: from 4.30, before 5.36 (fixed in 5.36); version 5.36 only
Zyxel VPN50 Firmware: from 4.30, before 5.36 (fixed in 5.36); version 5.36 only

Published 2023-05-24. Last modified 2026-06-17.