How severe is CVE-2023-33009?

CVE-2023-33009 has a CVSS 3.1 base score of 9.8 (CRITICAL). EPSS estimates a 28.1% probability of exploitation in the next 30 days. It is listed in the CISA Known Exploited Vulnerabilities catalog.

CVE-2023-33009: Zyxel Multiple Firewalls Buffer Overflow Vulnerability

CISA Known Exploited Vulnerabilities

Zyxel Multiple Firewalls Buffer Overflow Vulnerability is confirmed as actively exploited and is listed in the CISA KEV catalog.

Added to KEV

2023-06-05

Remediation due

2023-06-26

Required action
Apply updates per vendor instructions.

CISA notes
https://www.zyxel.com/global/en/support/security-advisories/zyxel-security-advisory-for-multiple-buffer-overflow-vulnerabilities-of-firewalls; https://nvd.nist.gov/vuln/detail/CVE-2023-33009

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.

Severity

CVSS 3.1 · CNA9.8 CRITICAL

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

SSVC · CISA-ADP

Exploitationactive

Automatableyes

Technical impacttotal

Exploitation Context

as of October 17, 2026

All KEV statistics→

CISA added CVE-2023-33009 to the KEV catalog 12 days after its CVE record was published. The median for entries added in 2023 is 12 days.
It is one of 13 Zyxel entries in the CISA KEV catalog, and one of 6 added in 2023.
Its current EPSS score (28.1%) is higher than that of 40% of CISA KEV entries.

Affected Products

Vendor	Product	Affected versions
Zyxel	Zyxel ATP series firmware	4.60 through 5.36 Patch 1
Zyxel	Zyxel USG FLEX series firmware	4.60 through 5.36 Patch 1
Zyxel	Zyxel USG FLEX 50(W) firmware	4.60 through 5.36 Patch 1
Zyxel	Zyxel USG20(W)-VPN firmware	4.60 through 5.36 Patch 1
Zyxel	Zyxel VPN series firmware	4.60 through 5.36 Patch 1
Zyxel	Zyxel ZyWALL/USG series firmware	4.60 through 4.73 Patch 1

References

1 Links

Other references

https://www.zyxel.com/global/en/support/security-advisories/zyxel-security-advisory-for-multiple-buffer-overflow-vulnerabilities-of-firewalls

Record Details

Published

2023-05-24

Last updated

2025-10-21

Assigner (CNA)

Zyxel

Credited to

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Tool categories

Fuzzing Binary Exploitation

CVE record data © The MITRE Corporation, used under the CVE Terms of Use. Exploited-in-the-wild data from the CISA Known Exploited Vulnerabilities catalog (CC0). Exploit prediction scores by FIRST EPSS (first.org/epss). This site is not endorsed or certified by MITRE, NVD, CISA, or FIRST.

CVE-2023-33009