IRONSMITHINTEL
CRITICALCVSS9.8
|
Actively Exploited
|CISA KEV|CVE-2023-33009|Auth: none — unauthenticated|Reboot: required|Manual only

Zyxel Multiple Firewalls Buffer Overflow Vulnerability (CVE-2023-33009)

Zyxel ATP, USG FLEX, USG FLEX 50(W), USG20(W)-VPN, VPN, and ZyWALL/USG firewalls contain a buffer overflow vulnerability in the notification function that could allow an unauthenticated attacker to cause denial-of-service (DoS) conditions and remote code execution on an affected device.

Published May 24, 2023 · Updated May 17, 2026
Why patchRisk explained in plain English
Worst-case scenarioIf unpatched

A remote attacker, without authentication, can achieve full data confidentiality loss, arbitrary modification of data, complete denial of service or system unavailability. Federal agencies are required to remediate by 2023-06-26 under CISA BOD 22-01.

How the attack worksNo clicks needed

This is a Classic Buffer Overflow (CWE-120) vulnerability in 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. Exploitation requires remote network access, low attack complexity, no authentication required, and no user interaction required.

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Phishing link

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Malicious file

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Server compromised

Am I affected?Quick check

Probably yes if any of these apply:

●IT Security
●Running atp100 firmware: 4.60 ≤ v < 5.36, 5.36; atp200 firmware: 4.60 ≤ v < 5.36, 5.36; atp500 firmware: 4.60 ≤ v < 5.36, 5.36; atp100w firmware: 4.60 ≤ v < 5.36, 5.36; atp700 firmware: 4.60 ≤ v < 5.36, 5.36; atp800 firmware: 4.60 ≤ v < 5.36, 5.36; usg flex 100 firmware: 4.60 ≤ v < 5.36, 5.36; usg flex 50 firmware: 4.60 ≤ v < 5.36, 5.36; usg flex 200 firmware: 4.60 ≤ v < 5.36, 5.36; usg flex 500 firmware: 4.60 ≤ v < 5.36, 5.36; usg flex 700 firmware: 4.60 ≤ v < 5.36, 5.36; usg flex 100w firmware: 4.60 ≤ v < 5.36, 5.36; usg flex 50w firmware: 4.60 ≤ v < 5.36, 5.36; usg 20w-vpn firmware: 4.60 ≤ v < 5.36, 5.36; vpn100 firmware: 4.60 ≤ v < 5.36, 5.36; vpn50 firmware: 4.60 ≤ v < 5.36, 5.36; vpn300 firmware: 4.60 ≤ v < 5.36, 5.36; vpn1000 firmware: 4.60 ≤ v < 5.36, 5.36; usg20-vpn firmware: 4.60 ≤ v < 5.36, 5.36; usg 40 firmware: 4.60 ≤ v < 4.73, 4.73; usg 40w firmware: 4.60 ≤ v < 4.73, 4.73; usg 60w firmware: 4.60 ≤ v < 4.73, 4.73; usg 60 firmware: 4.60 ≤ v < 4.73, 4.73
Real-world incidentsWhat we've seen

CISA added this CVE to the Known Exploited Vulnerabilities catalog on 2023-06-05 based on evidence of active exploitation in the wild. Federal agencies required to remediate by 2023-06-26.

How to patch

Manual remediation steps

1
Identify affected hosts: query inventory for general installs in scope.
2
Apply the vendor security update referenced in CVE-2023-33009's advisory. No specific KB/version is encoded yet — consult the linked MSRC/vendor URL.
3
Verify the fix per the vendor's published verification steps.
4
Document the remediation in your change ticket and re-scan with your vulnerability scanner to confirm closure.
PowerShell automationComing soon

No tested PowerShell script for this entry yet. We’re prioritising automation based on user demand.

References

↗ CVE-2023-33009↗ MSRC Advisory↗ NVD↗ Vendor Advisory