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ZldOperating system · Zyxel

CVE-2025-9133

HIGH · 8.1 CVSS v3.1 Published 2025-10-21
Fix available
A fix is available. Upgrade to 5.41 or later.
See remediation →
87/100
Remediation priority · High
Remotely reachable 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 missing authorization vulnerability in Zyxel ATP series firmware versions from V4.32 through V5.40, USG FLEX series firmware versions from V4.50 through V5.40, USG FLEX 50(W) series firmware versions from V4.16 through V5.40, and USG20(W)-VPN series firmware versions from V4.16 through V5.40 could allow a semi-authenticated attacker—who has completed only the first stage of the two-factor authentication (2FA) process—to view and download the system configuration from 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 missing authorization vulnerability in the two-factor authentication flow of Zyxel ATP, USG FLEX, and USG20(W)-VPN firewall firmware allows an attacker who has completed only the first stage of 2FA to bypass proper authorization checks and download the system configuration file from affected devices.

MitigationApply the vendor-supplied firmware update to a patched version (beyond V5.40) that properly validates authorization in the 2FA process before allowing access to system configuration downloads.

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
ZldOperating system
Affected:>= 4.32, < 5.41>= 4.50, < 5.41>= 4.16, < 5.41

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
Low
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
None

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

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 Zyxel firewall web interface or CLI and locate the device model information (ATP, USG FLEX, or USG20(W)-VPN series)
    Affected if Device is a Zyxel ATP, USG FLEX, or USG20(W)-VPN model
  2. Check the firmware version
    In the web interface, go to Maintenance > Firmware or use CLI command 'show system-info' to determine the installed Zyxel ZLD firmware version
    Affected if Firmware version is greater than or equal to 4.16 and less than 5.41 (any version from 4.16 through 5.40)
  3. Verify if two-factor authentication is configured
    In the web interface, go to Configuration > Object > Auth. Method > Two-Factor Authentication to check if 2FA is enabled for admin accounts
    Affected if Two-factor authentication is configured and enabled on the device
  4. Check management interface accessibility
    Review the firewall's management access settings in Configuration > Network > Management to see which IP addresses or networks can reach the admin interface
    Affected if The management interface is accessible from untrusted networks (such as the internet or public IP ranges)

The device is affected if it is an ATP, USG FLEX, or USG20(W)-VPN running firmware version 4.16 to 5.40, has two-factor authentication configured, and allows management access 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 5.41 or later
Fixed in 5.41
Interim mitigation

Apply the vendor-supplied firmware update to a patched version (beyond V5.40) that properly validates authorization in the 2FA process before allowing access to system configuration downloads.

Recommended fix High confidence

V5.41 or later firmware for the respective ATP, USG FLEX, USG FLEX 50(W), or USG20(W)-VPN series

  1. Identify the specific Zyxel device model (ATP, USG FLEX, USG FLEX 50W, or USG20W-VPN) currently deployed
  2. Access the device management interface or Zyxel support portal to obtain the firmware upgrade file
  3. Download the V5.41 or later firmware version specific to the device model
  4. Upload and apply the firmware upgrade following Zyxel's standard upgrade procedure
  5. After upgrade, verify the device is running firmware version 5.41 or later
  6. Confirm that the two-factor authentication (2FA) process now properly enforces authorization checks before allowing configuration access

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

Fix this in Zld Scoped from the published advisory
  • Consultation6.0 h
  • Implementation8.0 h
  • Testing8.0 h
  • Review / QA4.0 h
26.0 hours of engineering $4,560
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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-2025-9133 in production — separate from our analysis above.

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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