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CVE Record

CVE-2021-25660: A vulnerability has been identified in SIMATIC HMI Comfort Outdoor Panels V15 7\" & 15\" (incl.

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 server side when sending data from the client, which could result in a Denial-of-Service condition.

HighCVSS 7.5Not KEV-listedUpdated
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Glexia's TakeAutomated analysishigh

Security readout for executives and security teams

Plain-English summary

This Siemens issue can let an unauthenticated network client crash SmartVNC on affected SIMATIC HMI panels or WinCC Runtime Advanced systems. The documented impact is denial of service, not data theft or command execution. For industrial environments, HMI unavailability can still disrupt monitoring and operations.

Executive priority

Prioritize remediation for production HMIs or WinCC systems reachable from shared, remote-access, or less trusted networks. Treat as availability risk to industrial operations, especially where operator visibility depends on affected panels.

Technical view

SmartVNC contains an out-of-bounds memory access flaw triggered server-side by data sent from a client. The CVSS 3.1 vector is network reachable, low complexity, no privileges, no user interaction, with high availability impact only. Affected releases are Siemens SIMATIC HMI Comfort, Comfort Outdoor, KTP Mobile panels, and WinCC Runtime Advanced V15/V16 before specified updates.

Likely exposure

Exposure is most likely where affected Siemens HMI panels or WinCC Runtime Advanced systems run SmartVNC and are reachable over operational, maintenance, or remote-access networks.

Exploitation context

The source bundle does not show CISA KEV listing or other evidence of active exploitation. The flaw is network reachable and unauthenticated, but the documented impact is denial of service.

Researcher notes

Evidence supports denial of service through SmartVNC out-of-bounds memory access. The provided sources do not support confidentiality, integrity, code execution, public exploit availability, or active exploitation claims. Validation should stay focused on affected Siemens product families, versions, and network reachability.

Mitigation direction

  • Update V15 products to V15.1 Update 6 or later.
  • Update V16 products to V16 Update 4 or later.
  • Review Siemens SSA-538778 for product-specific guidance.
  • Limit SmartVNC exposure to trusted operational or maintenance networks.
  • Monitor HMI and WinCC Runtime availability for unexpected service disruption.

Validation and detection

  • Inventory SIMATIC HMI panels and WinCC Runtime Advanced deployments.
  • Confirm whether SmartVNC is enabled and network reachable.
  • Compare installed versions against affected version ranges listed by Siemens.
  • Verify V15 assets are at least V15.1 Update 6.
  • Verify V16 assets are at least V16 Update 4.
Prepared
Confidence
high
Sources
3

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.

ATT&CK lookup starting points

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cwe · low confidence lookup

CWE-788: Exact CWE lookup

Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.

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cve · low confidence lookup

CVE-2021-25660 mapping review

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Vulnerability profileCVE Program record
Severity
High
CVSS
7.5 (3.1)
Known Exploited
No
Published

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

Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

1CVSS vectors
3Timeline events
2ADP providers
2Source links

SSVC decision data

CISA-ADPCISA Coordinator
Timestamp
Version
2.0.3
Exploitation: noneAutomatable: yesTechnical Impact: partial

CVSS vector scores

1 official score

We collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.

ScoreVersionSeverityVectorExploitImpactSource
7.5CVSS 3.1HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H3.93.6CISA-ADP

Vulnerability scoring details

Base CVSS 3.1 score

7.5High
CVSS 3.1 vector shape for CVE-2021-25660Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

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

Attack Vector
NetworkAdjacentLocalPhysical
Attack Complexity
LowHigh
Privileges Required
NoneLowHigh
User Interaction
NoneRequired
Scope
ChangedUnchanged
Confidentiality Impact
HighLowNone
Integrity Impact
HighLowNone
Availability Impact
HighLowNone

Vulnerability timeline

Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.

  1. CVE reservedCVE Program

    The CVE ID was reserved by the assigning CNA.

  2. CVE publishedCVE Program

    The CVE record was published.

  3. CVE updatedCVE Program

    The CVE record metadata indicates this as the latest update time.

ADP provider summaries

CVECVE Program Container
CISA-ADPCISA ADP Vulnrichment
cvssV3_1other:ssvc

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
SiemensSIMATIC HMI Comfort Outdoor Panels V15 7\" & 15\" (incl. SIPLUS variants)All versions < V15.1 Update 6Listed
SiemensSIMATIC HMI Comfort Outdoor Panels V16 7\" & 15\" (incl. SIPLUS variants)All versions < V16 Update 4Listed
SiemensSIMATIC HMI Comfort Panels V15 4\" - 22\" (incl. SIPLUS variants)All versions < V15.1 Update 6Listed
SiemensSIMATIC HMI Comfort Panels V16 4\" - 22\" (incl. SIPLUS variants)All versions < V16 Update 4Listed
SiemensSIMATIC HMI KTP Mobile Panels V15 KTP400F, KTP700, KTP700F, KTP900 and KTP900FAll versions < V15.1 Update 6Listed
SiemensSIMATIC HMI KTP Mobile Panels V16 KTP400F, KTP700, KTP700F, KTP900 and KTP900FAll versions < V16 Update 4Listed
SiemensSIMATIC WinCC Runtime Advanced V15All versions < V15.1 Update 6Listed
SiemensSIMATIC WinCC Runtime Advanced V16All versions < V16 Update 4Listed
Weakness

CWE details

CWE-788

CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.