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Actively exploited in the wild. This CVE is on the CISA Known Exploited Vulnerabilities list — treat remediation as urgent. Federal remediation due by 26 Jun 2023.
Atp100 FirmwareOperating system · Zyxel

CVE-2023-33009

CRITICAL · 9.8 CVSS v3.1 Published 2023-05-24
Fix available
A fix is available. Upgrade to 5.36 or later.
See remediation →
100/100
Remediation priority · Urgent
In the wild Remotely reachable No privileges Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
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.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

A buffer overflow vulnerability exists in the notification function of multiple Zyxel network security device firmware versions (4.60-5.36 Patch 1 for ATP, USG FLEX, USG20(W)-VPN, VPN series; 4.60-4.73 Patch 1 for ZyWALL/USG). The flaw allows unauthenticated remote attackers to overflow a buffer in the notification handling code, potentially achieving remote code execution or causing denial-of-service conditions.

MitigationApply the latest firmware patches provided by Zyxel for all affected product series; if patches are unavailable, restrict network access to the management interface and monitor for indicators of compromise.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
Atp100 FirmwareOperating system
Affected:>= 4.60, < 5.36= 5.36
Atp200 FirmwareOperating system
Affected:>= 4.60, < 5.36= 5.36
Atp500 FirmwareOperating system
Affected:>= 4.60, < 5.36= 5.36
Atp100w FirmwareOperating system
Affected:>= 4.60, < 5.36= 5.36
Atp700 FirmwareOperating system
Affected:>= 4.60, < 5.36= 5.36
Atp800 FirmwareOperating system
Affected:>= 4.60, < 5.36= 5.36
Usg Flex 100 FirmwareOperating system
Affected:>= 4.60, < 5.36= 5.36
Usg Flex 50 FirmwareOperating system
Affected:>= 4.60, < 5.36= 5.36

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

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

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Identify the device model
    Access the device web interface under Status or Dashboard, or run 'show system-info' via CLI to confirm the model is one of: ATP100, ATP200, ATP500, ATP100w, ATP700, ATP800, USG Flex 100, USG Flex 50, USG20(W)-VPN, or ZyWALL/USG series
    Affected if Device model matches any of the listed affected models
  2. Check installed firmware version
    Navigate to Maintenance > Firmware in the web UI, or run 'show version' in CLI. Note the exact firmware version number
    Affected if Firmware version is 4.60, 4.65, 5.00, 5.10, 5.20, 5.25, 5.30, 5.35, 5.36, or any version >= 4.60 and < 5.36 Patch 1 (versions 5.36 Patch 1 and later are not affected)
  3. Determine if notification service is network-accessible
    Check firewall or network rules to see if the device management interface (HTTP/HTTPS ports 80/443 or custom management ports) is exposed to untrusted networks. Run 'show ip service' in CLI to list listening services
    Affected if The management interface or notification service ports are reachable from external/untrusted networks without proper access controls
  4. Verify notification feature configuration
    In the web UI, go to Configuration > Notification or similar section. In CLI, run 'show notification' or 'show running-config | include notification' to check if the notification function is configured and enabled
    Affected if Notification feature is enabled and configured, especially with external delivery methods (email, SMS, or cloud notification endpoints)
  5. Review recent access logs for notification exploits
    In the web UI, check Log > View Logs for unusual or mass connection attempts to notification-related endpoints. In CLI, run 'show log' with filters for notification or unusual authentication patterns
    Affected if Logs show unexpected connection patterns, malformed requests to notification handlers, or evidence of exploitation attempts

A user is affected if the device is a Zyxel ATP, USG FLEX, USG20(W)-VPN, VPN, or ZyWALL/USG model running firmware version 4.60 through 5.36 (inclusive), with the notification function accessible from untrusted networks.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 5.36 or later
Fixed in 5.36
Interim mitigation

Apply the latest firmware patches provided by Zyxel for all affected product series; if patches are unavailable, restrict network access to the management interface and monitor for indicators of compromise.

Recommended fix High confidence

Firmware version 5.36 Patch 1 or later (for ATP series, USG FLEX series, USG20(W)-VPN, VPN series, and ZyWALL/USG devices)

  1. Download the latest firmware version 5.36 Patch 1 or later from the official Zyxel support website (www.zyxel.com) for your specific device model
  2. Access the device web management interface or use CLI/console access
  3. Navigate to the firmware upgrade section (typically in Administration > Firmware or System > File Management)
  4. Upload and apply the firmware version 5.36 Patch 1 or newer
  5. After the device reboots, verify the firmware version has been successfully updated
  6. Confirm the device is functioning normally after the upgrade

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Atp100 Firmware Exploited in the wild — priority engagement
  • Consultation4.0 h
  • Implementation8.0 h
  • Testing6.0 h
  • Review / QA2.0 h
20.0 hours of engineering $3,500
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2023-33009 in production — separate from our analysis above.

No notes yet

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data