CVE-2021-35030

Script execution via unneutralized LLDP packet contents

Published Jul 26, 2021 · Updated Sep 17, 2024

Cross-site scripting in Zyxel GS1900-8 Firmware 2.60 allows physically proximate attackers to run script via crafted LLDP packets. The CGI program fails to neutralize LLDP packet contents before rendering them on certain management GUI pages, causing a browser to execute injected script. Exploitation requires a direct connection to the switch and a user to open an affected GUI page; no device takeover is reported.

CVSS severity4.3
Medium
EPSS probability0.27%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Cross-site scripting in Zyxel GS1900-8 Firmware 2.60 allows physically proximate attackers to run script via crafted LLDP packets. The CGI program fails to neutralize LLDP packet contents before rendering them on certain management GUI pages, causing a browser to execute injected script. Exploitation requires a direct connection to the switch and a user to open an affected GUI page; no device takeover is reported.

The record

CVE
CVE-2021-35030
Published
Jul 26, 2021
Updated
Sep 17, 2024
Vendor
Zyxel Networks
Product
GS1900-8 Firmware
Classifications
CWE-79, T1203
Attack vector
adjacent
Privileges
authenticated

Timeline

How it unfolded

  1. Jul 26, 2021CVE publishedPublication date reported by the CVE source.
  2. Sep 17, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=2.60

What conditions does exploitation require?

Attack vectoradjacent
Required privilegesauthenticated

What is affected?

Zyxel Networks · GS1900-8 Firmwareversion=2.60

Published CVSS scores

4.3NIST NVDCVSS:3.1/AV:A/AC:L/PR:H/UI:R/S:C/C:L/I:L/A:N
2.3NIST NVDAV:A/AC:M/Au:S/C:N/I:P/A:N
3.5Zyxel CorporationCVSS:3.1/AV:A/AC:L/PR:H/UI:N/S:U/C:N/I:L/A:L

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectoradjacent
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-79Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
T1203Exploitation for Client Execution

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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