CVE-2023-33009

CRITICAL9.8

CISA KEV

Published 2023-05-24 · Updated 2026-06-17 · Source security@zyxel.com.tw

Summary

CVE-2023-33009 is a critical-severity (CVSS 9.8) vulnerability in Zyxel Multiple Firewalls. CISA added it to the Known Exploited Vulnerabilities catalog on June 5, 2023, which means exploitation in the wild has been confirmed; US federal agencies had to remediate it by June 26, 2023. CISA does not currently list it as used in ransomware campaigns. Zyxel has 13 vulnerabilities in the KEV catalog, 2 of them linked to ransomware.

All 13 known-exploited Zyxel vulnerabilities →

Description

A buffer overflow vulnerability in the notification function in Zyxel ATP series firmware versions 4.60 through 5.36 Patch 1, USG FLEX series firmware versions 4.60 through 5.36 Patch 1, USG FLEX 50(W) firmware versions 4.60 through 5.36 Patch 1, USG20(W)-VPN firmware versions 4.60 through 5.36 Patch 1, VPN series firmware versions 4.60 through 5.36 Patch 1, ZyWALL/USG series firmware versions 4.60 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.

CVSS vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

CWE-120CWE-120

CISA Known-Exploited Vulnerability

Product: Zyxel — Multiple Firewalls

Name: Zyxel Multiple Firewalls Buffer Overflow Vulnerability

Date added: 2023-06-05 · Due: 2023-06-26

Required action: Apply updates per vendor instructions.

References

View on NVD

More exploited Zyxel vulnerabilities

Most recently added to CISA KEV

CVE-2026-7273
GS1900 Series Switches — Zyxel GS1900 Series Switches Stack-Based Buffer Overflow Vulnerability
added 2026-09-21
CVE-2024-40891
DSL CPE Devices — Zyxel DSL CPE OS Command Injection Vulnerability
added 2025-02-11
CVE-2024-40890
DSL CPE Devices — Zyxel DSL CPE OS Command Injection Vulnerability
added 2025-02-11
CVE-2024-11667
RANSOMWARE
Multiple Firewalls — Zyxel Multiple Firewalls Path Traversal Vulnerability
added 2024-12-03
CVE-2017-6884
RANSOMWARE
EMG2926 Routers — Zyxel EMG2926 Routers Command Injection Vulnerability
added 2023-09-18
CVE-2017-18368
P660HN-T1A Routers — Zyxel P660HN-T1A Routers Command Injection Vulnerability
added 2023-08-07

View all →

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