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Fencer Vulns
high 7.5

CVE-2021-33737 json

A vulnerability has been identified in SIMATIC CP 343-1 (incl.

published 2021-09-14 5 y ago modified 2026-06-17 4 mo ago also EUVD-2021-20414

cvss
7.5
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
1.1%
EPSS 1.1% chance of exploitation in 30 days, percentile 64%
public exploits
0
none known

Summary

A vulnerability has been identified in SIMATIC CP 343-1 (incl. SIPLUS variants) (All versions), SIMATIC CP 343-1 Advanced (incl. SIPLUS variants) (All versions), SIMATIC CP 343-1 ERPC (All versions), SIMATIC CP 343-1 Lean (incl. SIPLUS variants) (All versions), SIMATIC CP 443-1 (All versions < V3.3), SIMATIC CP 443-1 (All versions < V3.3), SIMATIC CP 443-1 Advanced (All versions < V3.3), SIPLUS NET CP 443-1 (All versions < V3.3), SIPLUS NET CP 443-1 Advanced (All versions < V3.3). Sending a specially crafted packet to port 102/tcp of an affected device could cause a denial of service condition. A restart is needed to restore normal operations.

Patch / fix

Vendor advisories

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

cisa ICSA-21-257-15 updated cvss 7.5

Siemens SIMATIC NET CP Modules

  • Siemens SIMATIC CP 343-1 (incl. SIPLUS variants) Siemens SIMATIC CP 343-1 Advanced (incl. SIPLUS variants) Siemens SIMATIC CP 343-1 ERPC (6GK7343-1FX00-0XE0) Siemens SIMATIC CP 343-1 Lean (incl. SIPLUS variants)
    affected: mitigation, no fix planned
  • Siemens SIMATIC CP 443-1 (6GK7443-1EX30-0XE0) <V3.3 Siemens SIMATIC CP 443-1 (6GK7443-1EX30-0XE1) <V3.3 Siemens SIMATIC CP 443-1 Advanced (6GK7443-1GX30-0XE0) <V3.3 Siemens SIPLUS NET CP 443-1 (6AG1443-1EX30-4XE0) <V3.3 Siemens SIPLUS NET CP 443-1 Advanced (6AG1443-1GX30-4XE0) <V3.3
    affected: fixed in V3.3, mitigation 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

1.06% chance of exploitation in the next 30 days, higher than 64% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H/E:P/RL:U/RC:C
CNA 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 7.8 AV:N/AC:L/Au:N/C:N/I:N/A:C

Affected products

  • Siemens SIMATIC CP 343-1 (incl. SIPLUS variants)
  • Siemens SIMATIC CP 343-1 Advanced (incl. SIPLUS variants)
  • Siemens SIMATIC CP 343-1 ERPC
  • Siemens SIMATIC CP 343-1 Lean (incl. SIPLUS variants)
  • Siemens SIMATIC CP 443-1
  • Siemens SIMATIC CP 443-1 Advanced
  • Siemens SIPLUS NET CP 443-1
  • Siemens SIPLUS NET CP 443-1 Advanced

Classification

Weakness
  • CWE-119 Improper Restriction of Operations within the Bounds of a Memory Buffer

References

Sources

Fencer Vulns 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.