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Vulnerability Assessment

Weakness
CWE
CWE-20
OWASP Top 10:2025
A05:2025 - Injection
ASVS 5.0
V2 - Validation and Business Logic Input validation, allowlisting
Impact

CVSS score of 8.1 (HIGH). Attack characteristics: network attack vector, low complexity, no privileges required, user interaction required.
Exploit ScenarioDerived

This vulnerability can be exploited remotely over the network. Successful exploitation could compromise the high-severity affected system.
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

The configuration parser of Zyxel ATP series firmware versions 5.10 through 5.35, USG FLEX series firmware versions 5.00 through 5.35, USG FLEX 50(W) firmware versions 5.10 through 5.35, USG20(W)-VPN. Rated high severity (CVSS 8.1), this vulnerability is remotely exploitable, 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. Apply vendor patches when available. Implement network segmentation and monitoring as interim mitigations.

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Technical ContextAI · show details

This vulnerability is classified under CWE-20. The configuration parser of Zyxel ATP series firmware versions 5.10 through 5.35, USG FLEX series firmware versions 5.00 through 5.35, USG FLEX 50(W) firmware versions 5.10 through 5.35, USG20(W)-VPN firmware versions 5.10 through 5.35, and VPN series firmware versions 5.00 through 5.35, which fails to properly sanitize user input. A remote unauthenticated attacker could leverage the vulnerability to modify device configuration data, resulting in DoS conditions on an affected device if the attacker could trick an authorized administrator to switch the management mode to the cloud mode. Affected products include: Zyxel Usg Flex 100 Firmware, Zyxel Usg Flex 100W Firmware, Zyxel Usg Flex 200 Firmware, Zyxel Usg Flex 50 Firmware, Zyxel Usg Flex 50W Firmware. Version information: through 5.35.

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Severity by source

NVD PRIMARY 8.1 HIGH
AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:H

Primary rating from NVD · only source for this CVE.

CVSS VectorNVD

Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
Required
Scope
Unchanged
Confidentiality
None
Integrity
High
Availability
High

DescriptionNVD

The configuration parser of Zyxel ATP series firmware versions 5.10 through 5.35, USG FLEX series firmware versions 5.00 through 5.35, USG FLEX 50(W) firmware versions 5.10 through 5.35, USG20(W)-VPN firmware versions 5.10 through 5.35, and VPN series firmware versions 5.00 through 5.35, which fails to properly sanitize user input. A remote unauthenticated attacker could leverage the vulnerability to modify device configuration data, resulting in DoS conditions on an affected device if the attacker could trick an authorized administrator to switch the management mode to the cloud mode.

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
Open
Automatable· derived
No
Human Impact· derived
Medium

Priority Score

41
Low Medium High Critical
KEV: 0
EPSS: +1
CVSS: +40
PoC: 0
Weaponized: 0
Threat intel: 0
Gov advisory: 0

Attack Technique

Information Disclosure MEDIUM

Information disclosure occurs when an application unintentionally exposes sensitive data that aids attackers in reconnaissance or directly compromises security.

Affected Products (CPE)NVD

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_50w_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:usg_flex_500_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:usg_flex_700_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:vpn100_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:vpn1000_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:vpn300_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:vpn50_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:usg_20w-vpn_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:atp100_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:atp100w_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:atp200_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:atp500_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:atp700_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:atp800_firmware:*:*:*:*:*:*:*:*

More in Usg 20W Vpn Firmware

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CVE-2023-33012 HIGH POC
8.8 Jul 17

A command injection vulnerability in the configuration parser of the Zyxel ATP series firmware versions 5.10 through 5.3
CVE-2023-33010 CRITICAL
9.8 May 24

A buffer overflow vulnerability in the ID processing function in Zyxel ATP series firmware versions 4.32 through 5.36 Pa
CVE-2023-33009 CRITICAL
9.8 May 24

A buffer overflow vulnerability in the notification function in Zyxel ATP series firmware versions 4.60 through 5.36 Pat
CVE-2023-33011 HIGH
8.8 Jul 17

A format string vulnerability in the Zyxel ATP series firmware versions 5.10 through 5.36 Patch 2, USG FLEX series firmw
CVE-2023-28767 HIGH
8.8 Jul 17

The configuration parser fails to sanitize user-controlled input in the Zyxel ATP series firmware versions 5.10 through

CVE-2023-27991 HIGH
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The post-authentication command injection vulnerability in the CLI command of Zyxel ATP series firmware versions 4.32 th
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CVE-2023-34138 HIGH
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CVE-2022-26532 HIGH
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CVE-2022-26531 HIGH
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Multiple improper input validation flaws were identified in some CLI commands of Zyxel USG/ZyWALL series firmware versio
CVE-2023-22917 HIGH
7.5 Apr 24

A buffer overflow vulnerability in the “sdwan_iface_ipc” binary of Zyxel ATP series firmware versions 5.10 through 5.32,
CVE-2023-22915 HIGH
7.5 Apr 24

A buffer overflow vulnerability in the “fbwifi_forward.cgi” CGI program of Zyxel USG FLEX series firmware versions 4.50

Same weakness CWE-20 – Improper Input Validation

View all
CVE-2021-44228 CRITICAL POC
10.0
CVE-2024-3400 CRITICAL POC
10.0
CVE-2022-47966 CRITICAL POC
9.8
CVE-2023-22515 CRITICAL POC
9.8
CVE-2009-0927 HIGH POC
8.8
CVE-2017-9791 CRITICAL POC
9.8
CVE-2017-15944 CRITICAL POC
9.8
CVE-2019-0604 CRITICAL POC
9.8

Same technique Information Disclosure

View all
CVE-2019-2725 CRITICAL POC
9.8
CVE-2021-34523 CRITICAL POC
9.0
CVE-2013-2251 CRITICAL POC
9.8
CVE-2017-5638 CRITICAL POC
9.8
CVE-2025-24813 CRITICAL POC
9.8
CVE-2025-68613 HIGH POC
8.8
CVE-2015-1701 HIGH POC
7.8
CVE-2017-0147 HIGH POC
7.5

References

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

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