How severe is CVE-2021-34570?

CVE-2021-34570 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.

Is CVE-2021-34570 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (57th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-34570?

CVE-2021-34570 primarily affects Phoenixcontact Plcnext Technology Starterkit Firmware. In total, 6 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2021-34570?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.

When was CVE-2021-34570 published?

CVE-2021-34570 was published on 2021-09-27 and last updated on 2026-06-17.

CVE-2021-34570

CVE-2021-34570 is a high-severity vulnerability in Phoenixcontact Plcnext Technology Starterkit Firmware with a CVSS 3.x base score of 7.5. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-20.

Key facts

Severity: High (CVSS 3.x base score 7.5)
CVSS v2: 7.8
EPSS exploit prediction: 1% (57th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-20
Affected product: Phoenixcontact Plcnext Technology Starterkit Firmware
Published: 2021-09-27
Last modified: 2026-06-17

Description

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.

Frequently asked questions

What is CVE-2021-34570?: 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.
How severe is CVE-2021-34570?: CVE-2021-34570 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.
Is CVE-2021-34570 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (57th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-34570?: CVE-2021-34570 primarily affects Phoenixcontact Plcnext Technology Starterkit Firmware. In total, 6 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2021-34570?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
When was CVE-2021-34570 published?: CVE-2021-34570 was published on 2021-09-27 and last updated on 2026-06-17.

References

https://cert.vde.com/en/advisories/VDE-2021-029/

Affected products (6)

cpe:2.3:o:phoenixcontact:plcnext_technology_starterkit_firmware:*:*:*:*:lts:*:*:*
cpe:2.3:o:phoenixcontact:axc_f_2152_starterkit_firmware:*:*:*:*:lts:*:*:*
cpe:2.3:o:phoenixcontact:rfc_4072s_firmware:*:*:*:*:lts:*:*:*
cpe:2.3:o:phoenixcontact:axc_f_3152_firmware:*:*:*:*:lts:*:*:*
cpe:2.3:o:phoenixcontact:axc_f_1152_firmware:*:*:*:*:lts:*:*:*
cpe:2.3:o:phoenixcontact:axc_f_2152_firmware:*:*:*:*:lts:*:*:*

Other CWE-20 (Improper Input Validation) vulnerabilities

CVE-2026-48316 — Critical (CVSS 10.0): ColdFusion versions 2025.9, 2023.20 and earlier are affected by an Improper Input Validation vulnerability that could…
CVE-2026-48281 — Critical (CVSS 10.0): ColdFusion versions 2025.9, 2023.20 and earlier are affected by an Improper Input Validation vulnerability that could…
CVE-2026-48277 — Critical (CVSS 10.0): ColdFusion versions 2025.9, 2023.20 and earlier are affected by an Improper Input Validation vulnerability that could…
CVE-2026-48055 — Critical (CVSS 10.0): Streambert is a cross-platform Electron Desktop App to stream and download any video media. In versions 2.4.0 and…
CVE-2026-34910 — Critical (CVSS 10.0): A malicious actor with access to the network could exploit an Improper Input Validation vulnerability found in UniFi OS…
CVE-2026-33587 — Critical (CVSS 10.0): Lack of user input sanitisation in Open Notebook v1.8.3 allows the application user to execute Python code (and…

Browse all CWE-20 (Improper Input Validation) vulnerabilities →