How severe is CVE-2021-35031?

CVE-2021-35031 has a CVSS 3.x base score of 6.8, rated medium severity. It is exploitable over an adjacent network with low attack complexity, requires high privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.

Is CVE-2021-35031 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (38th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-35031?

CVE-2021-35031 primarily affects Zyxel Gs1900-8 Firmware. In total, 14 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2021-35031?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.

When was CVE-2021-35031 published?

CVE-2021-35031 was published on 2021-12-28 and last updated on 2026-06-17.

CVE-2021-35031

CVE-2021-35031 is a medium-severity vulnerability in Zyxel Gs1900-8 Firmware with a CVSS 3.x base score of 6.8. 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: Medium (CVSS 3.x base score 6.8)
CVSS v2: 7.7
EPSS exploit prediction: 0% (38th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-78
Affected product: Zyxel Gs1900-8 Firmware
Published: 2021-12-28
Last modified: 2026-06-17

Description

A vulnerability in the TFTP client of Zyxel GS1900 series firmware, XGS1210 series firmware, and XGS1250 series firmware, which could allow an authenticated LAN user to execute arbitrary OS commands via the GUI of the vulnerable device.

Frequently asked questions

What is CVE-2021-35031?: A vulnerability in the TFTP client of Zyxel GS1900 series firmware, XGS1210 series firmware, and XGS1250 series firmware, which could allow an authenticated LAN user to execute arbitrary OS commands via the GUI of the vulnerable device.
How severe is CVE-2021-35031?: CVE-2021-35031 has a CVSS 3.x base score of 6.8, rated medium severity. It is exploitable over an adjacent network with low attack complexity, requires high privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.
Is CVE-2021-35031 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (38th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-35031?: CVE-2021-35031 primarily affects Zyxel Gs1900-8 Firmware. In total, 14 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2021-35031?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
When was CVE-2021-35031 published?: CVE-2021-35031 was published on 2021-12-28 and last updated on 2026-06-17.

References

https://www.zyxel.com/support/Zyxel_security_advisory_for_OS_command_injection_vulnerabilities_of_switches.shtml

Affected products (14)

cpe:2.3:o:zyxel:gs1900-8_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:gs1900-8hp_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:gs1900-10hp_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:gs1900-16_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:gs1900-24e_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:gs1900-24ep_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:gs1900-24_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:gs1900-24hp_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:gs1900-24hpv2_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:gs1900-48_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:gs1900-48hp_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:gs1900-48hpv2_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:xgs1210-12_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:xgs1250-12_firmware:*:*:*:*:*:*:*:*

More vulnerabilities in Zyxel Gs1900-8 Firmware

CVE-2019-15800 — Critical (CVSS 9.8): An issue was discovered on Zyxel GS1900 devices with firmware before 2.50(AAHH.0)C0. Due to lack of input validation in…
CVE-2019-15803 — Critical (CVSS 9.1): An issue was discovered on Zyxel GS1900 devices with firmware before 2.50(AAHH.0)C0. Through an undocumented sequence…
CVE-2026-7273 — High (CVSS 8.8): A stack-based buffer overflow vulnerability in the CGI program of Zyxel GS1900-48HPv2 firmware versions…
CVE-2019-15799 — High (CVSS 8.8): An issue was discovered on Zyxel GS1900 devices with firmware before 2.50(AAHH.0)C0. User accounts created through the…
CVE-2019-15804 — High (CVSS 7.5): An issue was discovered on Zyxel GS1900 devices with firmware before 2.50(AAHH.0)C0. By sending a signal to the CLI…
CVE-2019-15801 — High (CVSS 7.5): An issue was discovered on Zyxel GS1900 devices with firmware before 2.50(AAHH.0)C0. The firmware image contains…

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