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Vulnerability Assessment

Weakness
CWE
CWE-287
OWASP Top 10:2025
A07:2025 - Authentication Failures
ASVS 5.0
V6 - Authentication Authentication mechanism validation
MITRE ATT&CK

2 techniques across 2 tactics: Defense Evasion, Initial Access

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 9.8 (CRITICAL). Attack characteristics: network attack vector, low complexity, no privileges required, no user interaction not required.
Exploit ScenarioDerived

A remote attacker could bypass authentication mechanisms to gain unauthorized access by sending crafted requests to the affected application. No authentication is required to exploit this vulnerability.
Act Now Prioritize within 24-48h. Why: CRITICAL + EPSS > 30%, no patch available.
No patch listed yet 84.8% exploitation probability (EPSS)

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AnalysisAI

An authentication bypass vulnerability in the CGI program of Zyxel USG/ZyWALL series firmware versions 4.20 through 4.70, USG FLEX series firmware versions 4.50 through 5.20, ATP series firmware. Rated critical severity (CVSS 9.8), 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. Implement multi-factor authentication, enforce strong password policies, use proven authentication frameworks.

Affects your stack

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Technical ContextAI · show details

This vulnerability is classified as Improper Authentication (CWE-287), which allows attackers to bypass authentication mechanisms to gain unauthorized access. An authentication bypass vulnerability in the CGI program of Zyxel USG/ZyWALL series firmware versions 4.20 through 4.70, USG FLEX series firmware versions 4.50 through 5.20, ATP series firmware versions 4.32 through 5.20, VPN series firmware versions 4.30 through 5.20, and NSG series firmware versions V1.20 through V1.33 Patch 4, which could allow an attacker to bypass the web authentication and obtain administrative access of the device. Affected products include: Zyxel Usg40 Firmware, Zyxel Usg40W Firmware, Zyxel Usg60 Firmware, Zyxel Usg60W Firmware, Zyxel Zywall 110 Firmware. Version information: through 4.70.

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Severity by source

NVD PRIMARY 9.8 CRITICAL
AV:N/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
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

DescriptionNVD

An authentication bypass vulnerability in the CGI program of Zyxel USG/ZyWALL series firmware versions 4.20 through 4.70, USG FLEX series firmware versions 4.50 through 5.20, ATP series firmware versions 4.32 through 5.20, VPN series firmware versions 4.30 through 5.20, and NSG series firmware versions V1.20 through V1.33 Patch 4, which could allow an attacker to bypass the web authentication and obtain administrative access of the device.

Threat Intelligence Overview

EPSS Score
84.8%
Top 0% exploitable
Exploit
POC
Public exploit code exists
Data Quality
2 sources
Confidence: Low
NVD CVE.org EPSS POC (1)

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 CRITICAL
CISA KEV No
Public POC Yes
EPSS 84.8%
Patch available No
Active threat Yes
Deciding rule
CRITICAL + EPSS > 30%, no patch available
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
Poc
System Exposure· derived
Open
Automatable· derived
Yes
Human Impact· derived
Medium

Priority Score

154
Low Medium High Critical
KEV: 0
EPSS: +85
CVSS: +49
PoC: +20
Weaponized: 0
Threat intel: 0
Gov advisory: 0

Attack Technique

Authentication Bypass CRITICAL

Authentication bypass attacks exploit flaws in the verification mechanisms that control access to systems and applications.

Affected Products (CPE)NVD

cpe:2.3:o:zyxel:usg40_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:usg40w_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:usg60_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:usg60w_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:zywall_110_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:zywall_310_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:zywall_1100_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:usg_flex_100_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:usg_flex_200_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:usg_flex_500_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:usg_flex_100w_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:usg_flex_700_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:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:vpn50_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:vpn100_firmware:*:*:*:*:*:*:*:*
+ 5 more

More in Zywall 110 Firmware

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CVE-2019-12583 CRITICAL POC
9.1 Jun 27

Missing Access Control in the "Free Time" component of several Zyxel UAG, USG, and ZyWall devices allows a remote attack
CVE-2019-9955 MEDIUM POC
6.1 Apr 22

On Zyxel ATP200, ATP500, ATP800, USG20-VPN, USG20W-VPN, USG40, USG40W, USG60, USG60W, USG110, USG210, USG310, USG1100, U
CVE-2021-35029 CRITICAL
9.8 Jul 02

An authentication bypasss vulnerability in the web-based management interface of Zyxel USG/Zywall series firmware versio
CVE-2018-9129 MEDIUM
5.9 Aug 15

ZyXEL ZyWALL/USG series devices have a Bleichenbacher vulnerability in their Internet Key Exchange (IKE) handshake imple

Same weakness CWE-287 – Improper Authentication

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CVE-2022-40684 CRITICAL POC
9.8
CVE-2025-61882 CRITICAL POC
9.8
CVE-2020-0688 HIGH POC
8.8
CVE-2023-46805 HIGH POC
8.2
CVE-2023-35078 CRITICAL POC
9.8
CVE-2015-1187 CRITICAL POC
9.8
CVE-2024-7593 CRITICAL POC
9.8
CVE-2017-7921 CRITICAL POC
9.8

Same technique Authentication Bypass

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CVE-2015-3306 CRITICAL POC
10.0
CVE-2023-22515 CRITICAL POC
9.8
CVE-2012-4681 CRITICAL POC
9.8
CVE-2013-2465 CRITICAL POC
9.8
CVE-2011-3544 CRITICAL POC
9.8
CVE-2024-0012 CRITICAL POC
9.3

References

Advisories & patches
ADVISORY https://www.zyxel.com/support/Zyxel-security-advisory-for-authentication-bypass-vulnerability-of-firewalls.shtml

Search Externally

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