CVE-2023-27990Network attack vector

Browser script execution via stored Logs payload

Published Apr 24, 2023 · Updated Aug 2, 2024

Stored XSS in affected Zyxel ZLD firewall firmware allows remote authenticated users to run scripts through the Logs page. The management GUI persists administrator-supplied script content and renders it without neutralizing active markup when another user opens Logs; Zyxel does not identify the accepting parameter or handler. Administrator privileges are required to plant the payload, and a GUI visit triggers browser-context access to data or actions available to that session.

CVSS severity4.8
Medium
EPSS probability0.34%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Stored XSS in affected Zyxel ZLD firewall firmware allows remote authenticated users to run scripts through the Logs page. The management GUI persists administrator-supplied script content and renders it without neutralizing active markup when another user opens Logs; Zyxel does not identify the accepting parameter or handler. Administrator privileges are required to plant the payload, and a GUI visit triggers browser-context access to data or actions available to that session.

The record

CVE
CVE-2023-27990
Published
Apr 24, 2023
Updated
Aug 2, 2024
Vendor
Zyxel Networks
Product
Zyxel ATP Series Firmware
Classifications
CWE-79, T1203
Attack vector
network
Privileges
admin

Timeline

How it unfolded

  1. Apr 24, 2023CVE publishedPublication date reported by the CVE source.
  2. Aug 2, 2024Record 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=4.32 through 5.35

What conditions does exploitation require?

Attack vectornetwork
Required privilegesadmin

What is affected?

Zyxel Networks · Zyxel ATP Series Firmwareversion=4.32 through 5.35
Zyxel Networks · Zyxel USG FLEX 50(W) Firmwareversion=4.16 through 5.35
Zyxel Networks · Zyxel USG20(W)-VPN Firmwareversion=4.16 through 5.35
Zyxel Networks · Zyxel VPN Series Firmwareversion=4.30 through 5.35
Zyxel Networks · Zyxel USG FLEX Series Firmwareversion=4.50 through 5.35

Published CVSS scores

4.8Zyxel CorporationCVSS:3.1/AV:N/AC:L/PR:H/UI:R/S:C/C:L/I:L/A:N

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
Privilegesadmin
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-79Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
T1203Exploitation for Client Execution

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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