CVE-2021-21004 | Cross-site Scripting Vulnerability in Phoenix Contact FL SWITCH SMCS series products

In Phoenix Contact FL SWITCH SMCS series products in multiple versions an attacker may insert malicious code via LLDP frames into the web-based management which could then be executed by the client.

Published: 2021-06-25 Last update: 2026-06-16 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2021-21004 is rated Moderate Risk (45/100): CVSS High severity, with low exploitation likelihood (EPSS 0.58%). Review affected assets and schedule remediation.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2021-21004

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-06-15 0.24% 0.58% +0.34%
2 2025-03-17 0.06% 0.24% +0.18%
3 2023-03-07 — 0.06% —

Full EPSS history (7 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2021-21004

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
7.4 3.1 HIGH
CVSS:3.1/AV:A/AC:L/PR:N/UI:R/S:C/C:L/I:H/A:N Click to expand
Attack vector (AV:A)
Attacker has to be nearby on the network—same office, same link, that vibe—not the whole wide internet.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:R)
A real person has to do something—click, install, enable—otherwise it doesn’t land.
Scope (S:C)
Breaking this can reach past the original component and bite other resources—bigger blast radius.
Confidentiality (C:L)
Some sensitive info could get out, but not a total data dump.
Integrity (I:H)
They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:N)
Service keeps running; no real outage angle.
 2.1 4.7 [email protected]
6.1 3.1 MEDIUM
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:R)
A real person has to do something—click, install, enable—otherwise it doesn’t land.
Scope (S:C)
Breaking this can reach past the original component and bite other resources—bigger blast radius.
Confidentiality (C:L)
Some sensitive info could get out, but not a total data dump.
Integrity (I:L)
Attackers could change some data, but it’s limited—not everything goes.
Availability (A:N)
Service keeps running; no real outage angle.
 2.8 2.7 [email protected]
4.3 2.0 MEDIUM
AV:N/AC:M/Au:N/C:N/I:P/A:N Click to expand
Access vector (AV:N)
Can be exploited remotely over network reachability.
Access complexity (AC:M)
Exploitation needs some favorable conditions, but not exceptional ones.
Authentication (AU:N)
No authentication is required.
Confidentiality impact (C:N)
No confidentiality impact.
Integrity impact (I:P)
Partial integrity impact.
Availability impact (A:N)
No availability impact.
 8.6 2.9 [email protected]

Weakness enumeration for CVE-2021-21004

Affected software / configurations for CVE-2021-21004

Vendor Product Version Raw CPE
phoenixcontact fl_switch_smcs_16tx_firmware <= 4.70 cpe:2.3:o:phoenixcontact:fl_switch_smcs_16tx_firmware:*:*:*:*:*:*:*:*
phoenixcontact fl_switch_smcs_14tx\/2fx_firmware <= 4.70 cpe:2.3:o:phoenixcontact:fl_switch_smcs_14tx\/2fx_firmware:*:*:*:*:*:*:*:*
phoenixcontact fl_switch_smcs_14tx\/2fx-sm_firmware <= 4.70 cpe:2.3:o:phoenixcontact:fl_switch_smcs_14tx\/2fx-sm_firmware:*:*:*:*:*:*:*:*
phoenixcontact fl_switch_smcs_8gt_firmware <= 4.70 cpe:2.3:o:phoenixcontact:fl_switch_smcs_8gt_firmware:*:*:*:*:*:*:*:*
phoenixcontact fl_switch_smcs_6gt\/2sfp_firmware <= 4.70 cpe:2.3:o:phoenixcontact:fl_switch_smcs_6gt\/2sfp_firmware:*:*:*:*:*:*:*:*
phoenixcontact fl_switch_smcs_8tx-pn_firmware <= 4.70 cpe:2.3:o:phoenixcontact:fl_switch_smcs_8tx-pn_firmware:*:*:*:*:*:*:*:*
phoenixcontact fl_switch_smcs_4tx-pn_firmware <= 4.70 cpe:2.3:o:phoenixcontact:fl_switch_smcs_4tx-pn_firmware:*:*:*:*:*:*:*:*
phoenixcontact fl_switch_smcs_8tx_firmware <= 4.70 cpe:2.3:o:phoenixcontact:fl_switch_smcs_8tx_firmware:*:*:*:*:*:*:*:*
phoenixcontact fl_switch_smcs_6tx\/2sfp_firmware <= 4.70 cpe:2.3:o:phoenixcontact:fl_switch_smcs_6tx\/2sfp_firmware:*:*:*:*:*:*:*:*
phoenixcontact fl_switch_smn_6tx\/2pof-pn_firmware <= 4.70 cpe:2.3:o:phoenixcontact:fl_switch_smn_6tx\/2pof-pn_firmware:*:*:*:*:*:*:*:*
phoenixcontact fl_switch_smn_8tx-pn_firmware <= 4.70 cpe:2.3:o:phoenixcontact:fl_switch_smn_8tx-pn_firmware:*:*:*:*:*:*:*:*
phoenixcontact fl_switch_smn_6tx\/2fx_firmware <= 4.70 cpe:2.3:o:phoenixcontact:fl_switch_smn_6tx\/2fx_firmware:*:*:*:*:*:*:*:*
phoenixcontact fl_switch_smn_6tx\/2fx_sm_firmware <= 4.70 cpe:2.3:o:phoenixcontact:fl_switch_smn_6tx\/2fx_sm_firmware:*:*:*:*:*:*:*:*
phoenixcontact fl_nat_smn_8tx_firmware <= 4.63 cpe:2.3:o:phoenixcontact:fl_nat_smn_8tx_firmware:*:*:*:*:*:*:*:*
phoenixcontact fl_nat_smn_8tx-m_firmware <= 4.63 cpe:2.3:o:phoenixcontact:fl_nat_smn_8tx-m_firmware:*:*:*:*:*:*:*:*

References for CVE-2021-21004

URL Tags
https://cert.vde.com/en-us/advisories/vde-2021-023 Not Applicable Third Party Advisory
cvelogic Threat Intelligence