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Nbg6816 FirmwareOperating system · Zyxel

CVE-2021-4029

HIGH · 8.8 CVSS v3.1 Published 2022-02-24
Fix available
A fix is available. Upgrade to 1.00 or later.
See remediation →
93/100
Remediation priority · Urgent
No privileges 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 command injection vulnerability in the CGI program of the Zyxel ARMOR Z1/Z2 firmware could allow an attacker to execute arbitrary OS commands via a LAN interface.

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 command injection vulnerability exists in the CGI program of Zyxel ARMOR Z1/Z2 routers, allowing attackers with LAN access to execute arbitrary OS commands by injecting malicious input into the CGI interface.

MitigationApply vendor firmware updates when available; in the interim, restrict LAN access to the administrative interface via network segmentation or access control lists to limit exposure.

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
Nbg6816 FirmwareOperating system
Affected:= 1.00\(aawb.10\)c0
Nbg6817 FirmwareOperating system
Affected:< 1.00\(abcs.11\)c0

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
Adjacent
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:A/AC:L/PR:N/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 router model
    Locate the device model label on the router or access the web administrative interface to confirm the exact model number (e.g., Zyxel NBG6816, NBG6817, ARMOR Z1, or ARMOR Z2)
    Affected if The device is a Zyxel NBG6816, NBG6817, ARMOR Z1, or ARMOR Z2 model
  2. Check the installed firmware version
    Access the router web admin interface, navigate to the System or Status section, and record the firmware version displayed. Alternatively, use the router's command line or check the firmware file if manually uploaded.
    Affected if For NBG6816: firmware version equals 1.00(aawb.10)c0. For NBG6817: firmware version is lower than 1.00(abcs.11)c0.
  3. Verify CGI interface is enabled
    Access the router's web interface and attempt to access common CGI endpoints (e.g., /cgi-bin/, /webproc, or similar). Check the router's configuration for any CGI-related settings or service enabled status.
    Affected if The CGI web interface is accessible and responds to requests
  4. Confirm LAN-side accessibility of the admin interface
    From a host on the same LAN as the router, attempt to reach the router's web administrative interface using its local IP address (typically 192.168.1.1 or 192.168.0.1). Check if port 80 or 443 is open on the LAN-facing interface.
    Affected if The administrative web interface is reachable from LAN-side network segments without additional authentication barriers

The environment is affected if the device is a Zyxel NBG6816 running firmware 1.00(aawb.10)c0 or a NBG6817 running firmware below 1.00(abcs.11)c0, and the CGI administrative interface is accessible from the LAN.

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 1.00 or later
Fixed in 1.00
Interim mitigation

Apply vendor firmware updates when available; in the interim, restrict LAN access to the administrative interface via network segmentation or access control lists to limit exposure.

Recommended fix Moderate confidence

NBG6817: firmware version 1.00(abcs.11)c0 or later; NBG6816: firmware version later than 1.00(aawb.10)c0 (seek latest available from Zyxel)

  1. 1. Identify the exact model number (NBG6816 or NBG6817) of the affected Zyxel ARMOR device
  2. 2. Access the device's web management interface or download the firmware from Zyxel's official support website (www.zyxel.com)
  3. 3. Navigate to the firmware update section in the administration panel
  4. 4. Upload and install the patched firmware version
  5. 5. After upgrade, verify the device is functioning normally and confirm the new firmware version is applied
Caveat Standard firmware upgrade risks apply - ensure stable power during update and backup configuration if possible

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

Fix this in Nbg6816 Firmware Scoped from the published advisory
  • Consultation4.0 h
  • Implementation6.0 h
  • Testing8.0 h
  • Review / QA4.0 h
22.0 hours of engineering $3,800
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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-2021-4029 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