How severe is CVE-2021-4039?

CVE-2021-4039 has a CVSS 3.x base score of 9.8, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.

Is CVE-2021-4039 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 71% (99th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-4039?

CVE-2021-4039 affects Zyxel Nwa1100-nh Firmware. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2021-4039?

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

When was CVE-2021-4039 published?

CVE-2021-4039 was published on 2022-03-01 and last updated on 2026-06-17.

CVE-2021-4039

CVE-2021-4039 is a critical-severity vulnerability in Zyxel Nwa1100-nh Firmware with a CVSS 3.x base score of 9.8. Its EPSS exploit-prediction score of 71% places it in the 99th percentile, indicating an elevated likelihood of exploitation. The underlying weakness is classified as CWE-78.

Key facts

Severity: Critical (CVSS 3.x base score 9.8)
CVSS v2: 10.0
EPSS exploit prediction: 71% (99th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-78
Affected product: Zyxel Nwa1100-nh Firmware
Published: 2022-03-01
Last modified: 2026-06-17

Description

A command injection vulnerability in the web interface of the Zyxel NWA-1100-NH firmware could allow an attacker to execute arbitrary OS commands on the device.

Frequently asked questions

What is CVE-2021-4039?: A command injection vulnerability in the web interface of the Zyxel NWA-1100-NH firmware could allow an attacker to execute arbitrary OS commands on the device.
How severe is CVE-2021-4039?: CVE-2021-4039 has a CVSS 3.x base score of 9.8, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.
Is CVE-2021-4039 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 71% (99th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-4039?: CVE-2021-4039 affects Zyxel Nwa1100-nh Firmware. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2021-4039?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.
When was CVE-2021-4039 published?: CVE-2021-4039 was published on 2022-03-01 and last updated on 2026-06-17.

References

Affected products (1)

cpe:2.3:o:zyxel:nwa1100-nh_firmware:*:*:*:*:*:*:*:*

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CVE-2015-7256 — Medium (CVSS 5.9): ZyXEL NWA1100-N, NWA1100-NH, NWA1121-NI, NWA1123-AC, and NWA1123-NI access points; P-660HN-51, P-663HN-51,…

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