CVE-2021-4029

Unauthenticated OS command execution from adjacent networks

Published Feb 22, 2022 · Updated Aug 3, 2024

OS command injection in Zyxel ARMOR Z1 and Z2 firmware allows remote attackers on the LAN to execute arbitrary commands through a CGI program. Zyxel identifies the vulnerable locus only as a CGI program and has not disclosed the endpoint, input field, or unsafe command-construction operation. No authentication or user interaction is required, but access is limited to an adjacent LAN; exploitation grants command execution on the router.

CVSS severity8.8
High
EPSS probability0.75%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

OS command injection in Zyxel ARMOR Z1 and Z2 firmware allows remote attackers on the LAN to execute arbitrary commands through a CGI program. Zyxel identifies the vulnerable locus only as a CGI program and has not disclosed the endpoint, input field, or unsafe command-construction operation. No authentication or user interaction is required, but access is limited to an adjacent LAN; exploitation grants command execution on the router.

The record

CVE
CVE-2021-4029
Published
Feb 22, 2022
Updated
Aug 3, 2024
Vendor
Zyxel Networks
Product
ARMOR Z1 (NBG6816) firmware
Classifications
CWE-78, T1059
Attack vector
adjacent
Privileges
unauthenticated

Timeline

How it unfolded

  1. Feb 22, 2022CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 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=1.00(AAWB.10)C0

What conditions does exploitation require?

Attack vectoradjacent
Required privilegesunauthenticated

What is affected?

Zyxel Networks · ARMOR Z1 (NBG6816) firmwareversion=1.00(AAWB.10)C0
Zyxel Networks · ARMOR Z2 (NBG6817) firmwareversion=1.00(ABCS.10)C0

Published CVSS scores

8.3NIST NVDAV:A/AC:L/Au:N/C:C/I:C/A:C
8.8NIST NVDCVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
8.8Zyxel CorporationCVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/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)
Vectoradjacent
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-78Improper Neutralization of Special Elements used in an OS Command ('OS Command Injection')
T1059Command and Scripting Interpreter

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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