What’s Vulnerable › Vulnerabilities

CVE-2023-6397

• Severity: medium (CVSS 5.3 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.3% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2024-02-20 · updated 2026-06-17
• Weakness: CWE-476

Description

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; 5.37, 5.37-patch1 — fixed in 5.37
• Zyxel Atp100W Firmware: from 4.32 before 5.37; 5.37, 5.37-patch1 — fixed in 5.37
• Zyxel Atp200 Firmware: from 4.32 before 5.37; 5.37, 5.37-patch1 — fixed in 5.37
• Zyxel Atp500 Firmware: from 4.32 before 5.37; 5.37, 5.37-patch1 — fixed in 5.37
• Zyxel Atp700 Firmware: from 4.32 before 5.37; 5.37, 5.37-patch1 — fixed in 5.37
• Zyxel Atp800 Firmware: from 4.32 before 5.37; 5.37, 5.37-patch1 — fixed in 5.37
• Zyxel firewall (ZLD): from 4.50 before 5.37; 5.37, 5.37-patch1 — fixed in 5.37
• Zyxel Usg Flex 100Ax Firmware: from 4.50 before 5.37; 5.37, 5.37-patch1 — fixed in 5.37
• Zyxel Usg Flex 100H Firmware: from 4.50 before 5.37; 5.37, 5.37-patch1 — fixed in 5.37
• Zyxel USG FLEX 100(W) firmware: from 4.50 before 5.37; 5.37, 5.37-patch1 — fixed in 5.37
• Zyxel USG FLEX 200 firmware: from 4.50 before 5.37; 5.37, 5.37-patch1 — fixed in 5.37
• Zyxel Usg Flex 200H Firmware: from 4.50 before 5.37; 5.37, 5.37-patch1 — fixed in 5.37
• Zyxel Usg Flex 200Hp Firmware: from 4.50 before 5.37; 5.37, 5.37-patch1 — fixed in 5.37
• Zyxel USG FLEX 500 firmware: from 4.50 before 5.37; 5.37, 5.37-patch1 — fixed in 5.37
• Zyxel Usg Flex 500H Firmware: from 4.50 before 5.37; 5.37, 5.37-patch1 — fixed in 5.37
• Zyxel Usg Flex 50 Firmware: from 4.50 before 5.37; 5.37, 5.37-patch1 — fixed in 5.37
• Zyxel USG FLEX 50(W) firmware: from 4.50 before 5.37; 5.37, 5.37-patch1 — fixed in 5.37
• Zyxel USG FLEX 700 firmware: from 4.50 before 5.37; 5.37, 5.37-patch1 — fixed in 5.37
• Zyxel Usg Flex 700H Firmware: from 4.50 before 5.37; 5.37, 5.37-patch1 — fixed in 5.37

How to fix

Upgrade to a fixed version: Zyxel Atp100 Firmware 5.37; Zyxel Atp100W Firmware 5.37; Zyxel Atp200 Firmware 5.37; Zyxel Atp500 Firmware 5.37; Zyxel Atp700 Firmware 5.37; Zyxel Atp800 Firmware 5.37; Zyxel firewall (ZLD) 5.37; Zyxel Usg Flex 100Ax Firmware 5.37; Zyxel Usg Flex 100H Firmware 5.37; Zyxel USG FLEX 100(W) firmware 5.37; Zyxel USG FLEX 200 firmware 5.37; Zyxel Usg Flex 200H Firmware 5.37. Check the vendor advisory for mitigations.

References

• https://www.zyxel.com/global/en/support/security-advisories/zyxel-security-advisory-for-multiple-vulnerabilities-in-firewalls-and-aps-02-20-2024
• https://www.zyxel.com/global/en/support/security-advisories/zyxel-security-advisory-for-multiple-vulnerabilities-in-firewalls-and-aps-02-20-2024

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