CVE-2021-27386Network attack vector

Remote service interruption via client-side heap leak

Published May 12, 2021 · Updated Jun 2, 2026

Memory leak in SmartVNC on affected Siemens HMI and SINAMICS products allows remote attackers to interrupt service availability. The client-side device layout handler allocates heap memory while processing crafted VNC layout data but fails to release it after use. Network access to SmartVNC is sufficient; repeated malicious layout data exhausts memory and interrupts HMI or drive operation.

CVSS severity7.5
High
EPSS probability1.79%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Memory leak in SmartVNC on affected Siemens HMI and SINAMICS products allows remote attackers to interrupt service availability. The client-side device layout handler allocates heap memory while processing crafted VNC layout data but fails to release it after use. Network access to SmartVNC is sufficient; repeated malicious layout data exhausts memory and interrupts HMI or drive operation.

The record

CVE
CVE-2021-27386
Published
May 12, 2021
Updated
Jun 2, 2026
Vendor
Siemens
Product
SINAMICS GM150 (with option X30)
Classifications
CWE-401, T1499
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

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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 · 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

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.

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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-401Missing Release of Memory after Effective Lifetime
T1499Endpoint Denial of Service

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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