CVE-2021-33720

Severity: high (CVSS 7.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 1.0% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2021-09-14 · updated 2026-06-17
Weakness: CWE-120

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.

Affected products

Siemens Siprotec 5 With Cpu Variant Cp050: before 8.80 — fixed in 8.80
Siemens Siprotec 5 With Cpu Variant Cp100: before 8.80 — fixed in 8.80
Siemens Siprotec 5 With Cpu Variant Cp300: before 8.80 — fixed in 8.80

How to fix

Upgrade to a fixed version: Siemens Siprotec 5 With Cpu Variant Cp050 8.80; Siemens Siprotec 5 With Cpu Variant Cp100 8.80; Siemens Siprotec 5 With Cpu Variant Cp300 8.80. Check the vendor advisory for mitigations.

References

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