CVE-2023-33009Known exploitationNetwork attack vector

Remote code execution via notification buffer overflow

Published May 24, 2023 · Updated Oct 21, 2025

Buffer overflow in the notification function of Zyxel firewall firmware allows remote attackers to execute code or crash affected devices. Zyxel identifies the vulnerable locus as the notification function but has not published the input field, request path, or exact memory operation that overruns the buffer. Network reachability and no authentication are required; successful exploitation can execute code on the appliance or leave it unresponsive and interrupt VPN and firewall service.

CVSS severity9.8
Critical
EPSS probability28.14%
Next 30 days · Sep 16, 2026
Known exploitationReported
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Buffer overflow in the notification function of Zyxel firewall firmware allows remote attackers to execute code or crash affected devices. Zyxel identifies the vulnerable locus as the notification function but has not published the input field, request path, or exact memory operation that overruns the buffer. Network reachability and no authentication are required; successful exploitation can execute code on the appliance or leave it unresponsive and interrupt VPN and firewall service.

The record

CVE
CVE-2023-33009
Published
May 24, 2023
Updated
Oct 21, 2025
Vendor
Zyxel Networks
Product
Zyxel ATP Series Firmware
Classifications
CWE-120, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. May 24, 2023CVE publishedPublication date reported by the CVE source.
  2. Oct 21, 2025Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=4.60 through 5.36 Patch 1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Zyxel Networks · Zyxel ATP Series Firmwareversion=4.60 through 5.36 Patch 1
Zyxel Networks · Zyxel USG FLEX 50(W) Firmwareversion=4.60 through 5.36 Patch 1
Zyxel Networks · Zyxel USG20(W)-VPN Series Firmwareversion=4.60 through 5.36 Patch 1
Zyxel Networks · Zyxel ZyWALL/USG Series Firmwareversion=4.60 through 4.73 Patch 1
Zyxel Networks · Zyxel VPN Series Firmwareversion=4.60 through 5.36 Patch 1
Zyxel Networks · Zyxel USG FLEX Series Firmwareversion=4.60 through 5.36 Patch 1

Published CVSS scores

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

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationReported
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-120Buffer Copy without Checking Size of Input ('Classic Buffer Overflow')
T1190Exploit Public-Facing Application

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Reported exploitation

Technologies

Your stack

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Your stack

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