How severe is CVE-2021-33737?

CVE-2021-33737 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-2021-33737 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-2021-33737?

CVE-2021-33737 primarily affects Siemens Simatic Cp 343-1 Firmware. In total, 6 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2021-33737?

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-2021-33737 published?

CVE-2021-33737 was published on 2021-09-14 and last updated on 2026-06-17.

CVE-2021-33737

CVE-2021-33737 is a high-severity vulnerability in Siemens Simatic Cp 343-1 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-119.

Key facts

Severity: High (CVSS 3.x base score 7.5)
CVSS v2: 7.8
EPSS exploit prediction: 1% (60th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-119
Affected product: Siemens Simatic Cp 343-1 Firmware
Published: 2021-09-14
Last modified: 2026-06-17

Description

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.

Frequently asked questions

What is CVE-2021-33737?: 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.
How severe is CVE-2021-33737?: CVE-2021-33737 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-2021-33737 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-2021-33737?: CVE-2021-33737 primarily affects Siemens Simatic Cp 343-1 Firmware. In total, 6 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2021-33737?: 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-2021-33737 published?: CVE-2021-33737 was published on 2021-09-14 and last updated on 2026-06-17.

References

https://cert-portal.siemens.com/productcert/pdf/ssa-549234.pdf

Affected products (6)

cpe:2.3:o:siemens:simatic_cp_343-1_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:siemens:simatic_cp_343-1_advanced_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:siemens:simatic_cp_343-1_erpc_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:siemens:simatic_cp_343-1_lean_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:siemens:simatic_cp_443-1_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:siemens:simatic_cp_443-1_advanced_firmware:*:*:*:*:*:*:*:*

More vulnerabilities in Siemens Simatic Cp 343-1 Firmware

CVE-2015-8214 — Critical (CVSS 9.7): A vulnerability has been identified in SIMATIC NET CP 342-5 (incl. SIPLUS variants) (All versions), SIMATIC NET CP…
CVE-2016-8673 — High (CVSS 8.8): A vulnerability has been identified in SIMATIC CP 343-1 Advanced (incl. SIPLUS NET variant) (All versions < V3.0.53),…
CVE-2023-51440 — High (CVSS 7.5): A vulnerability has been identified in SIMATIC CP 343-1 (6GK7343-1EX30-0XE0) (All versions), SIMATIC CP 343-1 Lean…
CVE-2019-13946 — High (CVSS 7.5): Profinet-IO (PNIO) stack versions prior V06.00 do not properly limit internal resource allocation when multiple…
CVE-2018-4843 — Medium (CVSS 6.5): A vulnerability has been identified in SIMATIC S7-400 CPU 414-3 PN/DP V7 (All versions < V7.0.3), SIMATIC S7-400 CPU…
CVE-2016-8672 — Medium (CVSS 5.3): A vulnerability has been identified in SIMATIC CP 343-1 Advanced (incl. SIPLUS NET variant) (All versions < V3.0.53),…

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