CISA KEV · Known exploitedCritical

CVE-2023-28771

Zyxel Multiple Firewalls

Improper error message handling in Zyxel ZyWALL/USG series firmware versions 4.60 through 4.73, VPN series firmware versions 4.60 through 5.35, USG FLEX series firmware versions 4.60 through 5.35, and ATP series firmware versions 4.60 through 5.35, which could allow an unauthenticated attacker to execute some OS commands remotely by sending crafted packets to an affected device.

CVSS: 9.8
EPSS: 99.3%
CISA KEV: Listed
Published: 2023.04.25

PRIORITY ASSESSMENT

Immediate review

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

Known exploitationConfirmed by CISA KEV

Exploit probability99.3%

Technical severityCVSS 9.8

Vulnerability overview

Affected product and versions

Product: Zyxel Multiple Firewalls
Affected versions: 4.60 through 4.73, 4.60 through 5.35, >= 4.60 < 5.36, >= 4.60 < 5.35, >= 4.60 < 4.73, 4.73
Fixed versions: 5.36, 5.35, 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: 2023.06.21

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-78
KEV added: 2023.05.31
Ransomware use: 미확인