How severe is CVE-2021-33541?

CVE-2021-33541 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-2021-33541 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (73rd percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-33541?

CVE-2021-33541 primarily affects Phoenixcontact Ilc1x0 Firmware. In total, 2 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2021-33541?

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-2021-33541 published?

CVE-2021-33541 was published on 2021-06-25 and last updated on 2026-06-17.

CVE-2021-33541

CVE-2021-33541 is a high-severity vulnerability in Phoenixcontact Ilc1x0 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-770.

Key facts

Severity: High (CVSS 3.x base score 7.5)
CVSS v2: 7.8
EPSS exploit prediction: 1% (73rd percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-770
Affected product: Phoenixcontact Ilc1x0 Firmware
Published: 2021-06-25
Last modified: 2026-06-17

Description

Phoenix Contact Classic Line Controllers ILC1x0 and ILC1x1 in all versions/variants are affected by a Denial-of-Service vulnerability. The communication protocols and device access do not feature authentication measures. Remote attackers can use specially crafted IP packets to cause a denial of service on the PLC's network communication module. A successful attack stops all network communication. To restore the network connectivity the device needs to be restarted. The automation task is not affected.

Frequently asked questions

What is CVE-2021-33541?: Phoenix Contact Classic Line Controllers ILC1x0 and ILC1x1 in all versions/variants are affected by a Denial-of-Service vulnerability. The communication protocols and device access do not feature authentication measures. Remote attackers can use specially crafted IP packets to cause a denial of service on the PLC's network communication module. A successful attack stops all network communication. To restore the network connectivity the device needs to be restarted. The automation task is not affected.
How severe is CVE-2021-33541?: CVE-2021-33541 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-2021-33541 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (73rd percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-33541?: CVE-2021-33541 primarily affects Phoenixcontact Ilc1x0 Firmware. In total, 2 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2021-33541?: 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-2021-33541 published?: CVE-2021-33541 was published on 2021-06-25 and last updated on 2026-06-17.

References

https://cert.vde.com/en-us/advisories/vde-2021-019

Affected products (2)

cpe:2.3:o:phoenixcontact:ilc1x0_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:phoenixcontact:ilc1x1_firmware:*:*:*:*:*:*:*:*

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