What is the CVSS score of CVE-2021-35030?

CVE-2021-35030 has a CVSS 3.1 base score of 4.3 (Medium). CVSS vector: CVSS:3.1/AV:A/AC:L/PR:H/UI:R/S:C/C:L/I:L/A:N. EPSS exploitation probability: 0.3%.

Is there a patch available for CVE-2021-35030?

Yes, a patch is available for CVE-2021-35030. Update the affected software to the latest version immediately.

Gs1900 10Hp Firmware CVE-2021-35030

MEDIUM

Cross-site Scripting (XSS) (CWE-79)

2021-07-26 security@zyxel.com.tw

XSS 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

4.3

CVSS 3.1 · NVD

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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. Sign in to read
Impact	CVSS score of 4.3 (MEDIUM). Attack characteristics: adjacent network attack vector, low complexity, high privileges required, user interaction required.
Exploit ScenarioDerived	An attacker could exploit this vulnerability to inject malicious scripts into web pages viewed by other users.

This Month Plan within 30 days. Why: MEDIUM severity (CVSS 4.0-6.9).

Patch available 0.3% exploitation probability (EPSS)

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AnalysisAI

A vulnerability was found in the CGI program in Zyxel GS1900-8 firmware version V2.60, that did not properly sterilize packet contents and could allow an authenticated, local user to perform a. Rated medium severity (CVSS 4.3), this vulnerability is low attack complexity. This Cross-Site Scripting (XSS) vulnerability could allow attackers to inject malicious scripts into web pages viewed by other users.

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

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 Cross-Site Scripting (XSS) (CWE-79), which allows attackers to inject malicious scripts into web pages viewed by other users. A vulnerability was found in the CGI program in Zyxel GS1900-8 firmware version V2.60, that did not properly sterilize packet contents and could allow an authenticated, local user to perform a cross-site scripting (XSS) attack via a crafted LLDP packet. 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 4.3 MEDIUM

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

Primary rating from NVD · only source for this CVE.

CVSS VectorNVD

Attack Vector

Adjacent

Attack Complexity

Low

Privileges Required

High

User Interaction

Required

Scope

Changed

Confidentiality

Low

Integrity

Low

Availability

None

DescriptionNVD

Threat Intelligence Overview

EPSS Score

0.3%

Top 82% 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 MEDIUM

CISA KEV No

Public POC No

EPSS 0.3%

Patch available Yes

Active threat No

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

None

System Exposure· derived

Controlled

Automatable· derived

Human Impact· derived

Medium

Priority Score

Low Medium High Critical

KEV: 0

EPSS: 0

CVSS: +22

PoC: 0

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

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

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References

Advisories & patches

PATCH https://www.zyxel.com/support/Zyxel_security_advisory_for_XSS_vulnerability_of_GS1900_series_switches.shtml

Search Externally

GitHub PoC

Exploit-DB PacketStorm Snyk Rapid7 Nuclei Templates Trickest PoC

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