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Fencer Intel
high 7.5

CVE-2021-33720 json

A vulnerability has been identified in SIPROTEC 5 relays with CPU variants CP050 (All versions < V8.80), SIPROTEC 5 relays with CPU variant…

published 5y ago modified 4mo ago also EUVD-2021-20397

cvss
7.5
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
1.0%
EPSS 1.0% chance of exploitation in 30 days, percentile 64%
public exploits
0
none known

Summary

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.

Patch / fix

  • 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

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Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

cisa ICSA-21-257-10 updated cvss 5.3

Siemens SIPROTEC 5 relays (Update A)

  • Siemens SIPROTEC 5 relays with CPU variants CP050 <V8.80 Siemens SIPROTEC 5 relays with CPU variants CP100 <V8.80 Siemens SIPROTEC 5 relays with CPU variants CP300 <V8.80
    affected: fixed in V8.80, workaround support.industry.siemens.com

Facts from CISA's republication of the vendor's own advisory (CSAF); the linked advisory is the authoritative source. CISA notification · csaf

Exploit prediction

1.04% chance of exploitation in the next 30 days, higher than 64% of all scored CVEs (FIRST EPSS, 2026-11-09).

CVSS scores

assigned by version score vector
NVD 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
NVD 2.0 5.0 AV:N/AC:L/Au:N/C:N/I:N/A:P

Affected products

  • Siemens SIPROTEC 5 relays with CPU variants CP050
  • Siemens SIPROTEC 5 relays with CPU variants CP100
  • Siemens SIPROTEC 5 relays with CPU variants CP300

Classification

Weakness
  • CWE-120 Buffer Copy without Checking Size of Input

References

Sources

Fencer Intel keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.