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Atp100 FirmwareOperating system · Zyxel

CVE-2023-6398

HIGH · 7.2 CVSS v3.1 Published 2024-02-20
Fix available
A fix is available. Upgrade to 5.37 or later.
See remediation →
78/100
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 post-authentication command injection vulnerability in the file upload binary in Zyxel ATP series firmware versions from 4.32 through 5.37 Patch 1, USG FLEX series firmware versions from 4.50 through 5.37 Patch 1, USG FLEX 50(W) series firmware versions from 4.16 through 5.37 Patch 1, USG20(W)-VPN series firmware versions from 4.16 through 5.37 Patch 1, USG FLEX H series firmware versions from 1.10 through 1.10 Patch 1, NWA50AX firmware versions through 6.29(ABYW.3), WAC500 firmware versions through 6.65(ABVS.1), WAX300H firmware versions through 6.60(ACHF.1), and WBE660S firmware versions through 6.65(ACGG.1) could allow an authenticated attacker with administrator privileges to execute some operating system (OS) commands on an affected device via FTP.

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 post-authentication command injection vulnerability exists in the FTP file upload binary of multiple Zyxel device series (ATP, USG FLEX, USG FLEX 50W, USG20W-VPN, USG FLEX H, NWA50AX, WAC500, WAX300H, WBE660S). An authenticated attacker with administrator privileges can execute arbitrary OS commands by injecting them via the FTP upload functionality.

MitigationApply the latest vendor firmware patches to all affected devices. Until patches are available, restrict administrative access to trusted users only and monitor for suspicious FTP activity.

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:>= 4.32, < 5.37= 5.37
Atp100w FirmwareOperating system
Affected:>= 4.32, < 5.37= 5.37
Atp200 FirmwareOperating system
Affected:>= 4.32, < 5.37= 5.37
Atp500 FirmwareOperating system
Affected:>= 4.32, < 5.37= 5.37
Atp700 FirmwareOperating system
Affected:>= 4.32, < 5.37= 5.37
Atp800 FirmwareOperating system
Affected:>= 4.32, < 5.37= 5.37
Usg Flex 100 FirmwareOperating system
Affected:>= 4.50, < 5.37= 5.37
Usg Flex 100ax FirmwareOperating system
Affected:>= 4.50, < 5.37= 5.37

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

CVSS:3.1/AV:N/AC:L/PR:H/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 Zyxel device model
    Access the device web interface or CLI and retrieve the exact model name (e.g., ATP100, USG Flex 100, NWA50AX) from the system status or device info page
    Affected if The model matches one of the affected series: ATP, USG FLEX, USG FLEX 50W, USG20W-VPN, USG FLEX H, NWA50AX, WAC500, WAX300H, WBE660S
  2. Check the installed firmware version
    From the device web interface (System > Status) or CLI (show system info or version command), retrieve the current firmware version number
    Affected if The firmware version falls within the affected ranges: for ATP series (>= 4.32 and < 5.37, or exactly 5.37); for USG Flex 100/100ax (>= 4.50 and < 5.37, or exactly 5.37)
  3. Verify FTP upload functionality is accessible
    Check if the FTP upload feature is enabled in the device configuration (typically under Storage > FTP Server or File Management settings), and confirm the service is reachable from the network
    Affected if FTP upload is enabled and the service is accessible to the attacker (this is the vulnerable attack surface)
  4. Review logs for suspicious FTP activity
    Examine device logs (System > Log or CLI: show log) for unusual FTP upload events, especially those containing unexpected command strings, shell metacharacters, or commands originating from administrator sessions
    Affected if Logs show FTP upload activity containing injected OS commands, unexpected paths, or shell invocations that were not intentionally performed by administrators

The device is affected if it is a listed Zyxel model running a firmware version within the vulnerable ranges AND the FTP upload feature is accessible to an authenticated administrator.

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 5.37 or later
Fixed in 5.37
Interim mitigation

Apply the latest vendor firmware patches to all affected devices. Until patches are available, restrict administrative access to trusted users only and monitor for suspicious FTP activity.

Recommended fix High confidence

Firmware version 5.37 Patch 1 or later

  1. 1. Identify the current firmware version of the affected Zyxel device via the web management interface or CLI
  2. 2. Download the firmware version 5.37 Patch 1 (or later) from the official Zyxel support website (www.zyxel.com) for your specific model (ATP100, ATP100w, ATP200, ATP500, ATP700, ATP800, USG Flex 100, or USG Flex 100ax)
  3. 3. Back up the current device configuration before upgrading
  4. 4. Upload and apply the new firmware through the device's web interface or CLI (typically via System Maintenance > Firmware Upgrade)
  5. 5. After the device reboots, verify the firmware version has been updated successfully
  6. 6. Restore the configuration if needed and confirm the device is functioning properly

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

Fix this in Atp100 Firmware Scoped from the published advisory
  • Consultation3.0 h
  • Implementation6.0 h
  • Testing3.0 h
  • Review / QA2.0 h
14.0 hours of engineering $2,490
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Scan for this in your stack

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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-2023-6398 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