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Simatic Wincc Runtime AdvancedApplication · Siemens

CVE-2021-25661

HIGH · 7.5 CVSS v3.1 Published 2021-05-12
Fix available
A fix is available. Upgrade to 15.1 / 16 or later.
See remediation →
84/100
Remediation priority · High
Remotely reachable No privileges Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
A vulnerability has been identified in SIMATIC HMI Comfort Outdoor Panels V15 7\" & 15\" (incl. SIPLUS variants) (All versions < V15.1 Update 6), SIMATIC HMI Comfort Outdoor Panels V16 7\" & 15\" (incl. SIPLUS variants) (All versions < V16 Update 4), SIMATIC HMI Comfort Panels V15 4\" - 22\" (incl. SIPLUS variants) (All versions < V15.1 Update 6), SIMATIC HMI Comfort Panels V16 4\" - 22\" (incl. SIPLUS variants) (All versions < V16 Update 4), SIMATIC HMI KTP Mobile Panels V15 KTP400F, KTP700, KTP700F, KTP900 and KTP900F (All versions < V15.1 Update 6), SIMATIC HMI KTP Mobile Panels V16 KTP400F, KTP700, KTP700F, KTP900 and KTP900F (All versions < V16 Update 4), SIMATIC WinCC Runtime Advanced V15 (All versions < V15.1 Update 6), SIMATIC WinCC Runtime Advanced V16 (All versions < V16 Update 4). SmartVNC has an out-of-bounds memory access vulnerability that could be triggered on the client side when sending data from the server, which could result in a Denial-of-Service condition.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

The SmartVNC component in Siemens SIMATIC HMI panels and WinCC Runtime Advanced contains an out-of-bounds memory access vulnerability. When the VNC client receives specially crafted data from a malicious or compromised VNC server, it accesses memory outside allocated buffer bounds, causing a Denial-of-Service condition on the HMI device.

MitigationUpdate affected devices to the vendor-provided patched versions (V15.1 Update 6 or V16 Update 4). Until patches are applied, restrict network access to trusted VNC servers and monitor for anomalous VNC traffic.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
Simatic Wincc Runtime AdvancedApplication
Affected:< 16= 16< 15.1= 15.1
Simatic Hmi Comfort Outdoor Panels 7\" FirmwareOperating system
Affected:< 16= 16< 15.1= 15.1
Simatic Hmi Comfort Outdoor Panels 15\" FirmwareOperating system
Affected:< 16= 16< 15.1= 15.1
Simatic Hmi Comfort Panels 4\" FirmwareOperating system
Affected:< 16= 16< 15.1= 15.1
Simatic Hmi Comfort Panels 22\" FirmwareOperating system
Affected:< 16= 16< 15.1= 15.1
Simatic Hmi Ktp Mobile Panels Ktp400f FirmwareOperating system
Affected:< 16= 16< 15.1= 15.1
Simatic Hmi Ktp Mobile Panels Ktp700 FirmwareOperating system
Affected:< 16= 16< 15.1= 15.1
Simatic Hmi Ktp Mobile Panels Ktp700f FirmwareOperating system
Affected:< 16= 16< 15.1= 15.1

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Identify product and version
    Locate the installed Siemens SIMATIC software or HMI panel firmware version. For WinCC Runtime Advanced, check the installed software in Windows Programs and Features or the project properties. For HMI panels, access the device web page or use TIA Portal to read the firmware version.
    Affected if The version is WinCC Runtime Advanced or a listed HMI panel firmware at version 16, 15.1, or any version lower than 16 (excluding already-patched versions V15.1 Update 6 or later and V16 Update 4 or later).
  2. Verify SmartVNC client is in use
    Determine if the SmartVNC client feature is enabled or configured on the HMI device or WinCC Runtime Advanced. Check VNC connection settings, project configurations, or runtime settings for any VNC client connections.
    Affected if SmartVNC client functionality is actively enabled or configured to connect to VNC servers.
  3. Check network exposure of VNC client
    Review network configuration and firewall rules to determine whether the VNC client can communicate with external or untrusted VNC servers. Inspect any port configurations used for VNC communication.
    Affected if The VNC client can reach VNC servers across network boundaries without restriction to trusted sources.

A user is affected if they run an impacted version of WinCC Runtime Advanced or a listed HMI panel firmware AND have SmartVNC client functionality enabled, particularly if the device can connect to untrusted VNC servers.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

From vendor data
Upgrade available Upgrade to 15.1 / 16 or later
Fixed in 15.116
Interim mitigation

Update affected devices to the vendor-provided patched versions (V15.1 Update 6 or V16 Update 4). Until patches are applied, restrict network access to trusted VNC servers and monitor for anomalous VNC traffic.

Fix this in Simatic Wincc Runtime Advanced Scoped from the published advisory
  • Consultation4.0 h
  • Implementation4.0 h
  • Testing4.0 h
  • Review / QA2.0 h
14.0 hours of engineering $2,480
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2021-25661 in production — separate from our analysis above.

No notes yet

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data