CVE-2023-22916Network attack vector

Denial of service via unsanitized configuration input

Published Apr 24, 2023 · Updated Feb 12, 2025

Improper input validation in Zyxel ZLD firewall firmware allows remote attackers to modify device configuration data. The configuration parser accepts unsanitized input through cloud management and writes attacker-controlled data into the device configuration. The attack requires an authorized administrator to switch the appliance to cloud mode, and the resulting changes cause denial of service; WAN management is disabled by default.

CVSS severity8.1
High
EPSS probability0.69%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper input validation in Zyxel ZLD firewall firmware allows remote attackers to modify device configuration data. The configuration parser accepts unsanitized input through cloud management and writes attacker-controlled data into the device configuration. The attack requires an authorized administrator to switch the appliance to cloud mode, and the resulting changes cause denial of service; WAN management is disabled by default.

The record

CVE
CVE-2023-22916
Published
Apr 24, 2023
Updated
Feb 12, 2025
Vendor
Zyxel Networks
Product
Zyxel ATP Series Firmware
Classifications
CWE-20, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Apr 24, 2023CVE publishedPublication date reported by the CVE source.
  2. Feb 12, 2025Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

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

  1. Affected versionversion=5.10 through 5.35

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Zyxel Networks · Zyxel ATP Series Firmwareversion=5.10 through 5.35
Zyxel Networks · Zyxel USG FLEX 50(W) Firmwareversion=5.10 through 5.35
Zyxel Networks · Zyxel USG20(W)-VPN Firmwareversion=5.10 through 5.35
Zyxel Networks · Zyxel VPN Series Firmwareversion=5.00 through 5.35
Zyxel Networks · Zyxel USG FLEX Series Firmwareversion=5.00 through 5.35

Published CVSS scores

8.1NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:H
8.1Zyxel Networks CNACVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/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 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-20Improper Input Validation
T1499.004Application or System Exploitation

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.

Technologies

Your stack

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Your stack

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