CVE-2021-34570 | Phoenix Contact: DoS for PLCnext Control devices in versions prior to 2021.0.5 LTS

Multiple Phoenix Contact PLCnext control devices in versions prior to 2021.0.5 LTS are prone to a DoS attack through special crafted JSON requests.

Published: 2021-09-27 Last update: 2026-06-16 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2021-34570 is rated Moderate Risk (50.4/100): CVSS High 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-2021-34570

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% +0.65%
2 2026-01-26 0.45% 0.30% -0.15%
3 2025-11-21 — 0.45% —

Full EPSS history (14 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2021-34570

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
7.5 3.1 HIGH
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H 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:H)
Could take the service down hard or make it unusable for people who depend on it.
 3.9 3.6 [email protected]
7.5 3.1 HIGH
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H 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:H)
Could take the service down hard or make it unusable for people who depend on it.
 3.9 3.6 [email protected]
7.8 2.0 HIGH
AV:N/AC:L/Au:N/C:N/I:N/A:C 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:C)
Complete availability impact.
 10.0 6.9 [email protected]

Weakness enumeration for CVE-2021-34570

Affected software / configurations for CVE-2021-34570

Vendor Product Version Raw CPE
phoenixcontact plcnext_technology_starterkit_firmware < 2021.0.5 cpe:2.3:o:phoenixcontact:plcnext_technology_starterkit_firmware:*:*:*:*:lts:*:*:*
phoenixcontact axc_f_2152_starterkit_firmware < 2021.0.5 cpe:2.3:o:phoenixcontact:axc_f_2152_starterkit_firmware:*:*:*:*:lts:*:*:*
phoenixcontact rfc_4072s_firmware < 2021.0.5 cpe:2.3:o:phoenixcontact:rfc_4072s_firmware:*:*:*:*:lts:*:*:*
phoenixcontact axc_f_3152_firmware < 2021.0.5 cpe:2.3:o:phoenixcontact:axc_f_3152_firmware:*:*:*:*:lts:*:*:*
phoenixcontact axc_f_1152_firmware < 2021.0.5 cpe:2.3:o:phoenixcontact:axc_f_1152_firmware:*:*:*:*:lts:*:*:*
phoenixcontact axc_f_2152_firmware < 2021.0.5 cpe:2.3:o:phoenixcontact:axc_f_2152_firmware:*:*:*:*:lts:*:*:*

References for CVE-2021-34570

URL Tags
https://cert.vde.com/en/advisories/VDE-2021-029/ Patch Third Party Advisory
cvelogic Threat Intelligence