How severe is CVE-2023-33009?

CVE-2023-33009 has a CVSS score of 9.8/10, rated CRITICAL. Immediate patching is strongly recommended.

Which packages are affected by CVE-2023-33009?

Affected package information for CVE-2023-33009 is not yet fully mapped. Check the official advisory links for details.

How do I fix CVE-2023-33009?

No fixed version has been published for CVE-2023-33009 yet. Monitor the advisory for updates, apply mitigations recommended by the vendor, and use O3 Security to track when a fix becomes available in your stack.

Is CVE-2023-33009 actively exploited in the wild?

Yes. There are 1 known exploit references for CVE-2023-33009, including 1 in-the-wild exploitation observed on GitHub and other sources. Treat this as actively exploitable and prioritize patching immediately. All exploit code should only be run in an isolated sandbox environment for research or authorized testing — never against production systems without explicit written authorization.

What is the EPSS score for CVE-2023-33009?

CVE-2023-33009 has an EPSS (Exploit Prediction Scoring System) score of 5.6%, placing it in the 90th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

Is CVE-2023-33009 in the CISA Known Exploited Vulnerabilities catalog?

Yes. CVE-2023-33009 (Zyxel Multiple Firewalls Buffer Overflow Vulnerability) was added to CISA's Known Exploited Vulnerabilities (KEV) catalog on 2023-06-05. CISA required all US federal civilian agencies to remediate this vulnerability by 2023-06-26. The required action was: Apply updates per vendor instructions. Being listed in the KEV catalog is the strongest possible confirmation of active exploitation — treat this as a critical priority.

What type of vulnerability is CVE-2023-33009?

CVE-2023-33009 is classified as CWE-120 (CWE-120). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

Which products and versions are affected by CVE-2023-33009?

CVE-2023-33009 affects zyxel atp100 firmware (1 version, e.g. 5.36); zyxel atp100w firmware (1 version, e.g. 5.36); zyxel atp200 firmware (1 version, e.g. 5.36); zyxel atp500 firmware (1 version, e.g. 5.36), and 19 more product(s). Check the affected-products list on this page against your deployed version to confirm exposure.

When was CVE-2023-33009 published, and has it been updated?

CVE-2023-33009 was published on May 24, 2023 and was last updated on February 26, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

CVE-2023-33009: Atp100 Firmware CWE-120 (Critical 9.8)

EPSS Exploitation Probability

via FIRST.org ↗

5.6%probability of exploitation in next 30 days

Lower Risk90th percentile0.00%

EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.

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.

Affected Products

23 products · 69 configurations

OS

atp100 firmwarezyxel

≥ 4.60 && < 5.36

1 version

5.36

OS

atp100w firmwarezyxel

≥ 4.60 && < 5.36

1 version

5.36

OS

atp200 firmwarezyxel

≥ 4.60 && < 5.36

1 version

5.36

OS

atp500 firmwarezyxel

≥ 4.60 && < 5.36

1 version

5.36

OS

atp700 firmwarezyxel

≥ 4.60 && < 5.36

1 version

5.36

OS

atp800 firmwarezyxel

≥ 4.60 && < 5.36

1 version

5.36

Frequently Asked Questions

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.

O3 Security · Impact-Aware SCA

Is CVE-2023-33009 in your stack?

O3 detects CVE-2023-33009 across dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.

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