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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.

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Impact

CVSS score of 8.8 (HIGH). Attack characteristics: adjacent network attack vector, low complexity, no privileges required, no user interaction not required.
Exploit ScenarioDerived

An attacker could exploit this vulnerability to execute arbitrary operating system commands on the host. No authentication is required to exploit this vulnerability.
This Week Schedule remediation this week. Why: HIGH severity (CVSS 7.0-8.9).
No patch listed yet 0.7% exploitation probability (EPSS)

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AnalysisAI

A command injection vulnerability in the Free Time WiFi hotspot feature of the Zyxel USG FLEX series firmware versions 4.50 through 5.36 Patch 2 and VPN series firmware versions 4.20 through 5.36. Rated high severity (CVSS 8.8), this vulnerability is no authentication required, low attack complexity. No vendor patch available.

RemediationAI

No vendor patch is available at time of analysis. Monitor vendor advisories for updates. Avoid passing user input to shell commands. Use language-specific APIs instead of shell execution. Apply strict input validation with allowlists.

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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 command injection vulnerability in the Free Time WiFi hotspot feature of the Zyxel USG FLEX series firmware versions 4.50 through 5.36 Patch 2 and VPN series firmware versions 4.20 through 5.36 Patch 2, could allow an unauthenticated, LAN-based attacker to execute some OS commands on an affected device. Affected products include: Zyxel Usg 2200-Vpn Firmware, Zyxel Usg Flex 100 Firmware, Zyxel Usg Flex 100W Firmware, Zyxel Usg Flex 200 Firmware, Zyxel Usg Flex 50 Firmware. Version information: through 5.36.

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  • Exploit and PoC references, threat intelligence from 22 sources
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Severity by source

NVD PRIMARY 8.8 HIGH
AV:A/AC:L/PR:N/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
None
User Interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

DescriptionNVD

A command injection vulnerability in the Free Time WiFi hotspot feature of the Zyxel USG FLEX series firmware versions 4.50 through 5.36 Patch 2 and VPN series firmware versions 4.20 through 5.36 Patch 2, could allow an unauthenticated, LAN-based attacker to execute some OS commands on an affected device.

Threat Intelligence Overview

EPSS Score
0.7%
Top 51% 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 0.7%
Patch available No
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
No
Human Impact· derived
Medium

Priority Score

45
Low Medium High Critical
KEV: 0
EPSS: +1
CVSS: +44
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:usg_2200-vpn_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:usg_flex_100_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:usg_flex_100w_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:usg_flex_200_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:usg_flex_50_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:usg_flex_500_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:usg_flex_50w_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:usg_flex_700_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:zywall_vpn100_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:zywall_vpn2s_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:zywall_vpn300_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:zywall_vpn50_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:zywall_vpn_100_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:zywall_vpn_300_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:zywall_vpn_50_firmware:*:*:*:*:*:*:*:*

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Same weakness CWE-78 – OS Command Injection

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CVE-2019-15107 CRITICAL POC
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CVE-2018-11138 CRITICAL POC
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CVE-2014-6278 HIGH POC
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CVE-2020-9054 CRITICAL POC
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CVE-2017-6334 HIGH POC
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CVE-2024-50603 CRITICAL POC
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Same technique Command Injection

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CVE-2024-21887 CRITICAL POC
9.1
CVE-2016-3081 HIGH POC
8.1
CVE-2012-1823 CRITICAL POC
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CVE-2016-1555 CRITICAL POC
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CVE-2024-55956 CRITICAL POC
9.8

References

Advisories & patches
ADVISORY https://www.zyxel.com/global/en/support/security-advisories/zyxel-security-advisory-for-multiple-vulnerabilities-in-firewalls-and-wlan-controllers

Search Externally

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