CVE-2023-6397: Zyxel ATP100 Firmware

Medium severity, CVSS 5.3. EPSS: 0.3% chance of exploitation in the next 30 days.

A null pointer dereference vulnerability in Zyxel ATP series firmware versions from 4.32 through 5.37 Patch 1 and USG FLEX series firmware versions from 4.50 through 5.37 Patch 1 could allow a LAN-based attacker to cause denial-of-service (DoS) conditions by downloading a crafted RAR compressed file onto a LAN-side host if the firewall has the “Anti-Malware” feature enabled.

Affected products

  • Zyxel ATP100 Firmware: from 4.32, before 5.37 (fixed in 5.37); version 5.37 only
  • Zyxel ATP100W Firmware: from 4.32, before 5.37 (fixed in 5.37); version 5.37 only
  • Zyxel ATP200 Firmware: from 4.32, before 5.37 (fixed in 5.37); version 5.37 only
  • Zyxel ATP500 Firmware: from 4.32, before 5.37 (fixed in 5.37); version 5.37 only
  • Zyxel ATP700 Firmware: from 4.32, before 5.37 (fixed in 5.37); version 5.37 only
  • Zyxel ATP800 Firmware: from 4.32, before 5.37 (fixed in 5.37); version 5.37 only
  • Zyxel Usg Flex 100 Firmware: from 4.50, before 5.37 (fixed in 5.37); version 5.37 only
  • Zyxel Usg Flex 100ax Firmware: from 4.50, before 5.37 (fixed in 5.37); version 5.37 only
  • Zyxel Usg Flex 100h Firmware: from 4.50, before 5.37 (fixed in 5.37); version 5.37 only
  • Zyxel Usg Flex 100w Firmware: from 4.50, before 5.37 (fixed in 5.37); version 5.37 only
  • Zyxel Usg Flex 200 Firmware: from 4.50, before 5.37 (fixed in 5.37); version 5.37 only
  • Zyxel Usg Flex 200h Firmware: from 4.50, before 5.37 (fixed in 5.37); version 5.37 only
  • Zyxel Usg Flex 200hp Firmware: from 4.50, before 5.37 (fixed in 5.37); version 5.37 only
  • Zyxel Usg Flex 500 Firmware: from 4.50, before 5.37 (fixed in 5.37); version 5.37 only
  • Zyxel Usg Flex 500h Firmware: from 4.50, before 5.37 (fixed in 5.37); version 5.37 only
  • Zyxel Usg Flex 50 Firmware: from 4.50, before 5.37 (fixed in 5.37); version 5.37 only
  • Zyxel Usg Flex 50w Firmware: from 4.50, before 5.37 (fixed in 5.37); version 5.37 only
  • Zyxel Usg Flex 700 Firmware: from 4.50, before 5.37 (fixed in 5.37); version 5.37 only
  • Zyxel Usg Flex 700h Firmware: from 4.50, before 5.37 (fixed in 5.37); version 5.37 only

Published 2024-02-20. Last modified 2026-06-17.