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Vulnerability Assessment

Weakness
CWE
CWE-79
OWASP Top 10:2025
A05:2025 - Injection
ASVS 5.0
V1 - Encoding and Sanitization Output encoding, context-aware escaping
MITRE ATT&CK

2 techniques across 2 tactics: Initial Access, 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 6.1 (MEDIUM). Attack characteristics: network attack vector, low complexity, no privileges required, user interaction required. Public proof-of-concept exploit code is available.
Exploit ScenarioDerived

A remote attacker could inject malicious scripts into web pages viewed by other users by sending crafted requests to the affected application. No authentication is required to exploit this vulnerability.
This Month Plan within 30 days. Why: MEDIUM severity (CVSS 4.0-6.9).
Patch available 20.9% exploitation probability (EPSS)

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AnalysisAI

On Zyxel ATP200, ATP500, ATP800, USG20-VPN, USG20W-VPN, USG40, USG40W, USG60, USG60W, USG110, USG210, USG310, USG1100, USG1900, USG2200-VPN, ZyWALL 110, ZyWALL 310, ZyWALL 1100 devices, the security. Rated medium severity (CVSS 6.1), this vulnerability is remotely exploitable, no authentication required, low attack complexity. Public exploit code available.

RemediationAI

A vendor patch is available. Apply the latest security update as soon as possible. Sanitize all user input, use Content-Security-Policy headers, encode output contextually (HTML, JS, URL). Use frameworks with built-in XSS protection.

Affects your stack

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

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Technical ContextAI · show details

This vulnerability is classified as Cross-Site Scripting (XSS) (CWE-79), which allows attackers to inject malicious scripts into web pages viewed by other users. On Zyxel ATP200, ATP500, ATP800, USG20-VPN, USG20W-VPN, USG40, USG40W, USG60, USG60W, USG110, USG210, USG310, USG1100, USG1900, USG2200-VPN, ZyWALL 110, ZyWALL 310, ZyWALL 1100 devices, the security firewall login page is vulnerable to Reflected XSS via the unsanitized 'mp_idx' parameter. Affected products include: Zyxel Atp200 Firmware, Zyxel Atp500 Firmware, Zyxel Atp800 Firmware, Zyxel Usg20-Vpn Firmware, Zyxel Usg20W-Vpn Firmware.

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Severity by source

NVD PRIMARY 6.1 MEDIUM
AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

Primary rating from NVD · only source for this CVE.

CVSS VectorNVD

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

DescriptionNVD

On Zyxel ATP200, ATP500, ATP800, USG20-VPN, USG20W-VPN, USG40, USG40W, USG60, USG60W, USG110, USG210, USG310, USG1100, USG1900, USG2200-VPN, ZyWALL 110, ZyWALL 310, ZyWALL 1100 devices, the security firewall login page is vulnerable to Reflected XSS via the unsanitized 'mp_idx' parameter.

Threat Intelligence Overview

EPSS Score
20.9%
Top 3% exploitable
Exploit
POC
Public exploit code exists
Data Quality
3 sources
Confidence: Low
NVD CVE.org EPSS POC (1) Exploit-DB

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 MEDIUM
CISA KEV No
Public POC Yes
EPSS 20.9%
Patch available Yes
Active threat Yes
Deciding rule
MEDIUM severity (CVSS 4.0-6.9)
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
Poc
System Exposure· derived
Open
Automatable· derived
No
Human Impact· derived
Medium

Priority Score

71
Low Medium High Critical
KEV: 0
EPSS: +21
CVSS: +30
PoC: +20
Weaponized: 0
Threat intel: 0
Gov advisory: 0

Attack Technique

Cross-Site Scripting MEDIUM

Cross-Site Scripting occurs when an application accepts untrusted data and sends it to a web browser without proper validation or encoding.

Affected Products (CPE)NVD

cpe:2.3:o:zyxel:atp200_firmware:4.31:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:atp500_firmware:4.31:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:atp800_firmware:4.31:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:usg20-vpn_firmware:4.31:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:usg20w-vpn_firmware:4.31:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:usg40_firmware:4.31:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:usg40w_firmware:4.31:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:usg60_firmware:4.31:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:usg60w_firmware:4.31:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:usg110_firmware:4.31:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:usg210_firmware:4.31:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:usg310_firmware:4.31:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:usg1100_firmware:4.31:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:usg1900_firmware:4.31:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:usg2200-vpn_firmware:4.31:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:zywall_110_firmware:4.31:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:zywall_310_firmware:4.31:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:zywall_1100_firmware:4.31:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:vpn50_firmware:-:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:vpn100_firmware:-:*:*:*:*:*:*:*
+ 1 more

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Same weakness CWE-79 – Cross-site Scripting (XSS)

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CVE-2020-3580 MEDIUM POC
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CVE-2013-7389 MEDIUM POC
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CVE-2021-25299 MEDIUM POC
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CVE-2014-2120 MEDIUM
6.1
CVE-2023-40000 HIGH POC
8.3
CVE-2016-8581 MEDIUM POC
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CVE-2013-5223 MEDIUM POC
5.4
CVE-2025-52367 MEDIUM POC
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Same technique XSS

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CVE-2017-9248 CRITICAL POC
9.8
CVE-2013-1710 CRITICAL POC
10.0
CVE-2024-52875 HIGH POC
8.8

References

Advisories & patches
PATCH https://www.securitymetrics.com/blog/Zyxel-Devices-Vulnerable-Cross-Site-Scripting-Login-page ADVISORY https://www.zyxel.com/support/reflected-cross-site-scripting-vulnerability-of-firewalls.shtml REF http://seclists.org/fulldisclosure/2019/Apr/22

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