What is the CVSS score of CVE-2021-35031?

CVE-2021-35031 has a CVSS 3.1 base score of 8.0 (High). CVSS vector: CVSS:3.1/AV:A/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H. EPSS exploitation probability: 0.5%.

Is there a patch available for CVE-2021-35031?

Yes, a patch is available for CVE-2021-35031. Update the affected software to the latest version immediately.

Gs1900 10Hp Firmware CVE-2021-35031

HIGH

OS Command Injection (CWE-78)

2021-12-28 security@zyxel.com.tw

Command Injection Zyxel Gs1900 10Hp Firmware Gs1900 8 Firmware Gs1900 24 Firmware Gs1900 48Hpv2 Firmware Gs1900 8Hp Firmware Gs1900 16 Firmware Gs1900 24E Firmware Gs1900 24Ep Firmware Gs1900 24Hpv2 Firmware Gs1900 48 Firmware Gs1900 24Hp Firmware Gs1900 48Hp Firmware Xgs1210 12 Firmware Xgs1250 12 Firmware

8.0

CVSS 3.1 · NVD

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Vulnerability Assessment

Weakness	CWE CWE-78 OWASP Top 10:2025 A05:2025 - Injection ASVS 5.0 V1 - Encoding and Sanitization OS command sanitization, avoid shell exec MITRE ATT&CK 2 techniques across 1 tactic: Execution The technique list with ATT&CK links and the kill-chain view is part of the Basic plan and up. Sign in to read
Impact	CVSS score of 8.0 (HIGH). Attack characteristics: adjacent network attack vector, low complexity, low privileges required, no user interaction not required.
Exploit ScenarioDerived	An attacker could exploit this vulnerability to execute arbitrary operating system commands on the host.

This Week Schedule remediation this week. Why: HIGH severity (CVSS 7.0-8.9).

Patch available 0.5% exploitation probability (EPSS)

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AnalysisAI

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. Rated high severity (CVSS 8.0), this vulnerability is low attack complexity. This OS Command Injection vulnerability could allow attackers to execute arbitrary operating system commands on the host.

RemediationAI

A vendor patch is available. Apply the latest security update as soon as possible. Avoid passing user input to shell commands. Use language-specific APIs instead of shell execution. Apply strict input validation with allowlists.

Affects your stack

Find out whether the stacks and servers you run are on an affected version.

Checking this CVE against your own stacks and servers is part of the Basic plan and up.

Technical ContextAI · show details

This vulnerability is classified as OS Command Injection (CWE-78), which allows attackers to execute arbitrary operating system commands on the host. 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. Affected products include: Zyxel Gs1900-8 Firmware, Zyxel Gs1900-8Hp Firmware, Zyxel Gs1900-10Hp Firmware, Zyxel Gs1900-16 Firmware, Zyxel Gs1900-24E Firmware.

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Exploit and PoC references, threat intelligence from 22 sources

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Severity by source

NVD PRIMARY 8.0 HIGH

AV:A/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Primary rating from NVD · only source for this CVE.

CVSS VectorNVD

Attack Vector

Adjacent

Attack Complexity

Low

Privileges Required

Low

User Interaction

None

Scope

Unchanged

Confidentiality

High

Integrity

High

Availability

High

DescriptionNVD

Threat Intelligence Overview

EPSS Score

0.5%

Top 63% exploitable

Data Quality

2 sources

Confidence: Low

NVD

CVE.org

EPSS

How this decision was reached

The engine reads each signal below and applies a fixed list of rules from top to bottom. The first rule that matches sets the recommended action – like a statement, every line is shown.

SignalValue

Severity HIGH

CISA KEV No

Public POC No

EPSS 0.5%

Patch available Yes

Active threat No

Deciding rule

HIGH severity (CVSS 7.0-8.9)

What every action level means

Emergency Immediate action required. Criteria: CRITICAL + in CISA KEV (actively exploited) without patch, OR CRITICAL + EPSS > 30% without patch, OR CRITICAL + active threat signals without patch.

Act Now Prioritize within 24-48h. Criteria: in KEV with patch available, OR CRITICAL + public POC, OR HIGH + EPSS > 10%, OR CRITICAL + active threat, OR any CRITICAL severity.

This Week Schedule remediation this week. Criteria: HIGH severity (CVSS 7.0-8.9). Patch within normal change window.

This Month Plan within 30 days. Criteria: MEDIUM severity (CVSS 4.0-6.9), lower exploitation probability. Include in regular patch cycle.

Monitor Track and reassess. Criteria: LOW severity (CVSS 0.1-3.9), minimal exploitation risk. No immediate action needed.

SSVC AssessmentENISA

SSVC Decision· derived

Scheduled

Exploitation· derived

None

System Exposure· derived

Controlled

Automatable· derived

Human Impact· derived

Medium

Priority Score

Low Medium High Critical

KEV: 0

EPSS: 0

CVSS: +40

PoC: 0

Weaponized: 0

Threat intel: 0

Gov advisory: 0

Attack Technique

OS Command Injection CRITICAL

OS command injection occurs when an application passes unsanitized user input directly into system shell commands.

Affected Products (CPE)NVD

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:*:*:*:*:*:*:*:*

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References

Advisories & patches

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

Search Externally

GitHub PoC

Exploit-DB PacketStorm Snyk Rapid7 Nuclei Templates Trickest PoC

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