How severe is CVE-2021-4029?

CVE-2021-4029 has a CVSS 3.x base score of 8.8, rated high severity. It is exploitable over an adjacent network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.

Is CVE-2021-4029 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (53rd percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-4029?

CVE-2021-4029 primarily affects Zyxel Nbg6816 Firmware. In total, 2 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2021-4029?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.

When was CVE-2021-4029 published?

CVE-2021-4029 was published on 2022-02-24 and last updated on 2026-06-17.

CVE-2021-4029

CVE-2021-4029 is a high-severity vulnerability in Zyxel Nbg6816 Firmware with a CVSS 3.x base score of 8.8. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-78.

Key facts

Severity: High (CVSS 3.x base score 8.8)
CVSS v2: 8.3
EPSS exploit prediction: 1% (53rd percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-78
Affected product: Zyxel Nbg6816 Firmware
Published: 2022-02-24
Last modified: 2026-06-17

Description

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.

Frequently asked questions

What is CVE-2021-4029?: 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.
How severe is CVE-2021-4029?: CVE-2021-4029 has a CVSS 3.x base score of 8.8, rated high severity. It is exploitable over an adjacent network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.
Is CVE-2021-4029 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (53rd percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-4029?: CVE-2021-4029 primarily affects Zyxel Nbg6816 Firmware. In total, 2 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2021-4029?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
When was CVE-2021-4029 published?: CVE-2021-4029 was published on 2022-02-24 and last updated on 2026-06-17.

References

https://www.zyxel.com/support/forgery-vulnerabilities-of-select-Armor-home-routers.shtml

Affected products (2)

cpe:2.3:o:zyxel:nbg6816_firmware:1.00\(aawb.10\)c0:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:nbg6817_firmware:*:*:*:*:*:*:*:*

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