CVE-2021-21003 | Denial of Service Vulnerability in Phoenix Contact FL SWITCH SMCS series products

In Phoenix Contact FL SWITCH SMCS series products in multiple versions fragmented TCP-Packets may cause a Denial of Service of Web-, SNMP- and ICMP-Echo services. The switching functionality of the device is not affected.

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-2021-21003 is rated Moderate Risk (41.5/100): CVSS Medium severity, with medium exploitation likelihood (EPSS 0.95%). 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-2021-21003

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 0.30% 0.95% +0.64%
2 2025-03-30 0.36% 0.30% -0.06%
3 2025-03-29 — 0.36% —

Full EPSS history (9 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2021-21003

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
5.3 3.1 MEDIUM
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L 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:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:N)
Doesn’t really leak secrets in a meaningful way.
Integrity (I:N)
Data isn’t meaningfully altered or forged.
Availability (A:L)
Might cause slowdowns, glitches, or partial disruption—not a full brick.
 3.9 1.4 [email protected]
5.3 3.1 MEDIUM
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L 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:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:N)
Doesn’t really leak secrets in a meaningful way.
Integrity (I:N)
Data isn’t meaningfully altered or forged.
Availability (A:L)
Might cause slowdowns, glitches, or partial disruption—not a full brick.
 3.9 1.4 [email protected]
5.0 2.0 MEDIUM
AV:N/AC:L/Au:N/C:N/I:N/A:P Click to expand
Access vector (AV:N)
Can be exploited remotely over network reachability.
Access complexity (AC:L)
Exploitation conditions are straightforward and predictable.
Authentication (AU:N)
No authentication is required.
Confidentiality impact (C:N)
No confidentiality impact.
Integrity impact (I:N)
No integrity impact.
Availability impact (A:P)
Partial availability impact.
 10.0 2.9 [email protected]

Weakness enumeration for CVE-2021-21003

Affected software / configurations for CVE-2021-21003

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-2021-21003

cvelogic Threat Intelligence