CVE-2021-33737Network attack vector

Unauthenticated device halt via malformed port 102 packet

Published Sep 14, 2021 · Updated Aug 3, 2024

Memory-bounds error in Siemens SIMATIC NET CP modules allows remote attackers to halt device operation with a crafted port 102/tcp packet. The port 102/tcp packet-processing path performs a memory-buffer operation outside its intended bounds; Siemens has not disclosed the exact parser. No authentication or user interaction is required, and successful exploitation leaves the communications processor unavailable until restart.

CVSS severity7.5
High
EPSS probability1.06%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Memory-bounds error in Siemens SIMATIC NET CP modules allows remote attackers to halt device operation with a crafted port 102/tcp packet. The port 102/tcp packet-processing path performs a memory-buffer operation outside its intended bounds; Siemens has not disclosed the exact parser. No authentication or user interaction is required, and successful exploitation leaves the communications processor unavailable until restart.

The record

CVE
CVE-2021-33737
Published
Sep 14, 2021
Updated
Aug 3, 2024
Vendor
Siemens
Product
SIMATIC CP 343-1 Lean
Classifications
CWE-119, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Sep 14, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=All versions

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Siemens · SIMATIC CP 343-1 Leanversion=All versions
Siemens · SIPLUS NET CP 443-1version=All versions < V3.3
Siemens · SIMATIC CP 343-1 ERPCversion=All versions
Siemens · SIMATIC CP 343-1 Advancedversion=All versions
Siemens · SIMATIC CP 443-1version=All versions < V3.3
Siemens · SIPLUS NET CP 443-1 Advancedversion=All versions < V3.3
Siemens · SIMATIC CP 443-1 Advancedversion=All versions < V3.3
Siemens · SIMATIC CP 343-1version=All versions

Published CVSS scores

7.8NVDAV:N/AC:L/Au:N/C:N/I:N/A:C
7.5Siemens ProductCERTCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
7.5NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-119Improper Restriction of Operations within the Bounds of a Memory Buffer
T1499.004Endpoint Denial of Service: Application or System Exploitation

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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