CISA KEV · Known exploitedCritical

CVE-2023-33009

Zyxel Multiple Firewalls

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: 9.8
EPSS: 28.1%
CISA KEV: Listed
Published: 2023.05.24

PRIORITY ASSESSMENT

Immediate review

CISA has listed this vulnerability in the Known Exploited Vulnerabilities catalog.

Known exploitationConfirmed by CISA KEV

Exploit probability28.1%

Technical severityCVSS 9.8

Vulnerability overview

Affected product and versions

Product: Zyxel Multiple Firewalls
Affected versions: 4.60 through 5.36 Patch 1, 4.60 through 4.73 Patch 1, >= 4.60 < 5.36, 5.36, >= 4.60 < 4.73, 4.73
Fixed versions: 5.36, 4.73

Recommended response sequence

Confirm exposure before applying a vendor-supported change.

Full remediation guide

CISA required action

Apply updates per vendor instructions.

Due date: 2023.06.26

1
Identify
Confirm that Zyxel Multiple Firewalls and an affected version are present.
2
Prioritize
Combine exploitation signals with asset exposure and business criticality.
3
Remediate
Follow the vendor advisory or supported update path and preserve rollback options.
4
Verify
Recheck the version, service health, access paths, and relevant logs.

Technical data

CVSS vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
CWE: CWE-120
KEV added: 2023.06.05
Ransomware use: 미확인