How severe is CVE-2021-33720?

CVE-2021-33720 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-2021-33720 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (60th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-33720?

CVE-2021-33720 primarily affects Siemens Siprotec 5 With Cpu Variant Cp050. In total, 3 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2021-33720?

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-2021-33720 published?

CVE-2021-33720 was published on 2021-09-14 and last updated on 2026-06-17.

CVE-2021-33720

CVE-2021-33720 is a high-severity vulnerability in Siemens Siprotec 5 With Cpu Variant Cp050 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-120.

Key facts

Severity: High (CVSS 3.x base score 7.5)
CVSS v2: 5.0
EPSS exploit prediction: 1% (60th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-120
Affected product: Siemens Siprotec 5 With Cpu Variant Cp050
Published: 2021-09-14
Last modified: 2026-06-17

Description

A vulnerability has been identified in SIPROTEC 5 relays with CPU variants CP050 (All versions < V8.80), SIPROTEC 5 relays with CPU variants CP100 (All versions < V8.80), SIPROTEC 5 relays with CPU variants CP300 (All versions < V8.80). Specially crafted packets sent to port 4443/tcp could cause a Denial-of-Service condition.

Frequently asked questions

What is CVE-2021-33720?: A vulnerability has been identified in SIPROTEC 5 relays with CPU variants CP050 (All versions < V8.80), SIPROTEC 5 relays with CPU variants CP100 (All versions < V8.80), SIPROTEC 5 relays with CPU variants CP300 (All versions < V8.80). Specially crafted packets sent to port 4443/tcp could cause a Denial-of-Service condition.
How severe is CVE-2021-33720?: CVE-2021-33720 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-2021-33720 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (60th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-33720?: CVE-2021-33720 primarily affects Siemens Siprotec 5 With Cpu Variant Cp050. In total, 3 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2021-33720?: 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-2021-33720 published?: CVE-2021-33720 was published on 2021-09-14 and last updated on 2026-06-17.

References

https://cert-portal.siemens.com/productcert/pdf/ssa-847986.pdf

Affected products (3)

cpe:2.3:o:siemens:siprotec_5_with_cpu_variant_cp050:*:*:*:*:*:*:*:*
cpe:2.3:o:siemens:siprotec_5_with_cpu_variant_cp100:*:*:*:*:*:*:*:*
cpe:2.3:o:siemens:siprotec_5_with_cpu_variant_cp300:*:*:*:*:*:*:*:*

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