CVE-2021-21004

Client-side script execution via unneutralized LLDP data

Published Jun 25, 2021 · Updated Sep 16, 2024

Cross-site scripting in Phoenix Contact FL SWITCH and FL NAT firmware allows attackers to execute scripts in a management client via LLDP. The web-based management interface renders malicious code injected through LLDP frames without neutralizing it before client-side execution. Affected firmware is 4.70 and earlier for FL SWITCH models and 4.63 and earlier for FL NAT models; exploitation requires local-network access and user interaction, and the script runs in the management client context.

CVSS severity7.4
High
EPSS probability0.58%
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 Phoenix Contact FL SWITCH and FL NAT firmware allows attackers to execute scripts in a management client via LLDP. The web-based management interface renders malicious code injected through LLDP frames without neutralizing it before client-side execution. Affected firmware is 4.70 and earlier for FL SWITCH models and 4.63 and earlier for FL NAT models; exploitation requires local-network access and user interaction, and the script runs in the management client context.

The record

CVE
CVE-2021-21004
Published
Jun 25, 2021
Updated
Sep 16, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-79, T1059.007
Attack vector
adjacent
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jun 25, 2021CVE publishedPublication date reported by the CVE source.
  2. Sep 16, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectoradjacent
Required privilegesunauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

6.1NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
7.4Phoenix ContactCVSS:3.0/AV:A/AC:L/PR:N/UI:R/S:C/C:L/I:H/A:N
4.3NIST NVDAV:N/AC:M/Au:N/C:N/I:P/A:N

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
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-79Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
T1059.007Command and Scripting Interpreter: JavaScript/JScript

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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