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Simatic Wincc Runtime AdvancedApplication · Siemens

CVE-2021-25662

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 client fails to handle an exception properly if the program execution process is modified after sending a packet 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 client component in affected SIMATIC HMI products fails to properly handle exceptions when program execution is modified after the server sends a packet. This improper exception handling leads to a denial-of-service condition, causing the client to crash or become unresponsive.

MitigationApply Siemens vendor patches by updating to V15.1 Update 6 or V16 Update 4 (or later) for the respective product versions. As a compensating control, restrict network access to the VNC server and monitor for DoS symptoms.

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 the SIMATIC HMI product model
    Locate the product nameplate, check system information in the HMI runtime, or review procurement documentation to confirm the exact model (e.g., Simatic HMI Comfort Panels 7", Ktp700f, WinCC Runtime Advanced)
    Affected if The product model matches any of the affected products listed in the CVE (various Comfort Outdoor Panels, Comfort Panels, Ktp Mobile Panels, or WinCC Runtime Advanced)
  2. Determine the installed firmware or software version
    Access the HMI control panel or system settings to view the firmware version; for WinCC Runtime Advanced, check the software version in the Windows Add/Remove Programs or the application properties
    Affected if The installed version is < 16, = 16, < 15.1, or = 15.1 (i.e., versions 15.1, 16, or any version before 16)
  3. Verify SmartVNC client is enabled or configured
    Check the HMI project settings or VNC server configuration for SmartVNC client connections; inspect the runtime configuration for VNC client functionality
    Affected if SmartVNC client feature is enabled and the HMI is configured to act as a VNC client connecting to a VNC server
  4. Check network exposure of VNC services
    Review network configuration, firewall rules, or port mappings to determine if the HMI VNC server/client ports (typically 5900+) are accessible from untrusted networks
    Affected if The VNC server or client component is exposed to network-accessible paths without proper segmentation or access controls

If the product is a listed SIMATIC HMI model running firmware/software version 16 or earlier (including version 15.1), and the SmartVNC client is enabled, the environment is affected by this CVE.

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

Apply Siemens vendor patches by updating to V15.1 Update 6 or V16 Update 4 (or later) for the respective product versions. As a compensating control, restrict network access to the VNC server and monitor for DoS symptoms.

Fix this in Simatic Wincc Runtime Advanced Scoped from the published advisory
  • Consultation2.0 h
  • Implementation4.0 h
  • Testing4.0 h
  • Review / QA2.0 h
12.0 hours of engineering $2,080
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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-2021-25662 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