CVE-2021-37185Network attack vector

Unauthenticated PLC denial of service via crafted packets

Published Feb 9, 2022 · Updated Apr 18, 2025

Resource-lifetime handling flaws in Siemens SIMATIC controllers allow remote attackers to halt PLC operation via crafted TCP/102 packets. Siemens identifies operation on an expired or released resource but does not disclose the affected routine or resource. No authentication or user interaction is required, and each affected PLC must be restarted to restore operation.

CVSS severity7.5
High
EPSS probability2.06%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Resource-lifetime handling flaws in Siemens SIMATIC controllers allow remote attackers to halt PLC operation via crafted TCP/102 packets. Siemens identifies operation on an expired or released resource but does not disclose the affected routine or resource. No authentication or user interaction is required, and each affected PLC must be restarted to restore operation.

The record

CVE
CVE-2021-37185
Published
Feb 9, 2022
Updated
Apr 18, 2025
Vendor
Siemens
Product
SIMATIC S7-1500 CPU
Classifications
CWE-672, T0814
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Feb 9, 2022CVE publishedPublication date reported by the CVE source.
  2. Apr 18, 2025Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

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

  1. Affected versionversion=All versions >= V2.9.2 < V2.9.4

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Siemens · SIMATIC S7-1500 CPUversion=All versions >= V2.9.2 < V2.9.4
Siemens · SIMATIC ET 200SP Open Controller CPU 1515SP PC2version=All versions >= V21.9 < V21.9.4
Siemens · TIM 1531 IRCversion=All versions < V2.3.6
Siemens · SIMATIC S7-PLCSIM Advancedversion=All versions >= V4.0 < V4.0 SP1
Siemens · SIMATIC S7-1500 Software Controllerversion=All versions >= V21.9 < V21.9.4
Siemens · SIPLUS TIM 1531 IRCversion=All versions < V2.3.6
Siemens · SIMATIC S7-1200 CPUversion=All versions >= V4.5.0 < V4.5.2
Siemens · SIMATIC Drive Controllerversion=All versions >= V2.9.2 < V2.9.4

Published CVSS scores

7.1NVDAV:N/AC:M/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

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-672Operation on a Resource after Expiration or Release
T0814Denial of Service

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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