KEV Intelligence

Vulnerability report

Exploited in the wild Confirmed confidence In CISA KEV

CVE-2023-33009

ATP series firmware Denial of Service

Zyxel / ATP series firmware · 4.60 through 5.36 Patch 1

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Severity
CVSS 9.8 · Critical
Confidence
Confirmed
Exploit status
Exploited in the wild
EPSS
28.1%
First observed
—
Last observed
—

Decision summary

What security teams need to know first

Direct answers before the deeper technical record.

What it is

CVE-2023-33009 is an unauthenticated vulnerability affecting Zyxel ATP series firmware and 5 other products. A buffer overflow vulnerability in the notification function in Zyxel ATP series firmware versions 4.60...

Is it exploited?

Yes. KEV Intelligence tracks this CVE as a known exploited vulnerability. Confidence is confirmed.

Who is affected?

Zyxel / ATP series firmware 4.60 through 5.36 patch 1.

What should we do?

Prioritize remediation. Validate affected assets and apply vendor fixes on an accelerated timeline.

Overview

ATP series firmware Denial of Service

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.

Vendor Product Affected Status
Zyxel ATP series firmware 4.60 through 5.36 Patch 1 Affected
Zyxel USG FLEX series firmware 4.60 through 5.36 Patch 1 Affected
Zyxel USG FLEX 50(W) firmware 4.60 through 5.36 Patch 1 Affected
Zyxel USG20(W)-VPN firmware 4.60 through 5.36 Patch 1 Affected
Zyxel VPN series firmware 4.60 through 5.36 Patch 1 Affected
Zyxel ZyWALL/USG series firmware 4.60 through 4.73 Patch 1 Affected
Published
24 May 2023
Exploitation Reported
05 Jun 2023
Attack vector
Remote
Complexity
Low
Privileges
None
User interaction
None

Tags

nessus_scanner cisa edge

CVE References

Exploitation evidence

Why KEV Intelligence marks this CVE as exploited

Third-party attestation and first-party sensor observation are shown separately so teams can judge the evidence chain.

Exploited in the wild

CISA

Recorded 05 Jun 2023

Independent exploitation attestation added to the KEV Intelligence record.

Known exploited vulnerability sources

Per-source evidence links for KEV attestations are available through the KEV Intelligence Pro API.

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Source Added
CISA First 2023-06-05 00:00 UTC

Detection

Operational artifacts and observed signals

Make the evidence actionable in scanner, SOC, and edge-control workflows.

Observed signals

Request targets
0
User-Agents
0

Raw values available in Pro and Enterprise.

Virtual patch status

No KEV Intelligence virtual patch is currently available. Future rules ship for ModSecurity, Cloudflare, and AWS WAF.

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Scanner Artifacts

Scanner and exploit-framework references linked to this CVE.

Scanner Reference Detected
Nessus https://www.tenable.com/plugins/nessus/176416 02 Jun 2025

Risk and context

Severity, weaknesses, and research context

CVSS v3.1

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

EPSS

28.1%

Weaknesses

Buffer Copy without Checking Size of Input ('Classic Buffer Overflow') CWE-120

Timeline

From disclosure to observed exploitation

  1. Nessus plugin available

    Scanner coverage available

  2. Added to CISA KEV

    Listed in the CISA Known Exploited Vulnerabilities catalog

  3. CVE published

    Vulnerability disclosed publicly

  4. CVE ID reserved

    Identifier reserved by the CNA

Pro API

Automate this intelligence

Confidence, exploit status, sensor telemetry, PoCs, scanner integrations, mentions, and tags are available programmatically for VM, SOC, and CTI workflows.

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  • Evidence confidence and provenance
  • First-party sensor telemetry
  • PoC and scanner references
  • Affected versions and enrichment
  • Automation-ready JSON delivery

GET /api/v2/pro/kevs/CVE-2023-33009

Free JSON includes basic KEV fields 
{
  "cve_id": "CVE-2023-33009",
  "confidence": "Confirmed",
  "cvss_score": 9.8,
  "cvss_estimated": false,
  "epss_score": 0.28144,
  "exploit_status": {
    "exploited_in_the_wild": true,
    "active_exploitation_observed": false
  },
  "sensor_telemetry": { "attempts": 0, "sensors": 0 }
}

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