CVE-2021-27385Network attack vector

HMI service hang via device-layout infinite loop

Published May 12, 2021 · Updated Jun 2, 2026

Uncontrolled resource consumption in Siemens SIMATIC HMI, WinCC, and SINAMICS products allows remote attackers to hang affected HMI systems. The SmartVNC client-side device layout handler accepts crafted packets that drive resource consumption into an infinite loop. Network reachability is required; on SINAMICS products, Sm@rtServer is disabled by default, and exploitation interrupts HMI availability.

CVSS severity7.5
High
EPSS probability2.56%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Uncontrolled resource consumption in Siemens SIMATIC HMI, WinCC, and SINAMICS products allows remote attackers to hang affected HMI systems. The SmartVNC client-side device layout handler accepts crafted packets that drive resource consumption into an infinite loop. Network reachability is required; on SINAMICS products, Sm@rtServer is disabled by default, and exploitation interrupts HMI availability.

The record

CVE
CVE-2021-27385
Published
May 12, 2021
Updated
Jun 2, 2026
Vendor
Siemens
Product
SINAMICS GM150 (with option X30)
Classifications
CWE-400, CWE-835, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. May 12, 2021CVE publishedPublication date reported by the CVE source.
  2. Jun 2, 2026Record 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

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Siemens · SINAMICS GM150 (with option X30)version=All versions
Siemens · SIMATIC WinCC Runtime Advancedversion=All versions < V15.1 Update 6; version=All versions < V16 Update 4
Siemens · SIMATIC HMI Comfort Outdoor Panelsversion=All versions < V15.1 Update 6; version=All versions < V16 Update 4
Siemens · SINAMICS GH150version=All versions
Siemens · SINAMICS SL150version=All versions
Siemens · SINAMICS SM120version=All versions
Siemens · SIMATIC HMI Comfort Panelsversion=All versions < V15.1 Update 6; version=All versions < V16 Update 4
Siemens · SINAMICS SM150iversion=All versions
Siemens · SINAMICS GL150 (with option X30)version=All versions
Siemens · SINAMICS SM150version=All versions
Siemens · SINAMICS SH150version=All versions
Siemens · SIMATIC HMI KTP Mobile Panelsversion=All versions < V15.1 Update 6; version=All versions < V16 Update 4

Published CVSS scores

7.5NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
5.0NIST NVDAV:N/AC:L/Au:N/C:N/I:N/A:P

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-400Uncontrolled Resource Consumption
CWE-835Loop with Unreachable Exit Condition ('Infinite Loop')
T1499.004Application 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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